SPAM!!!!

Every quarter Google and Postini take a joint look at the state of the spam industry, its undulations and upheavals. And the results for the most recent quarter, ended June 30, are in.

In many ways, the results are unsurprising: Spam is up again, with levels 53 percent higher than the first quarter of the year, but just 6 percent higher than the second quarter of 2008. (Spam levels were uncommonly low last quarter following the shut-down of the ISP McColo, a notorious haven for spammers. Those spammers have largely found other services to host their activities, and spam levels have since rebounded.)

But rising spam levels are not exactly a surprise. The big news in the latest figures is the return of spammers to traditional, almost "old school" methods.

One of the big ones is the sudden reemergence of image spam, a very simple form of spam in which the advertisement or message is embedded into an image inside an email. Image spam became common in 2007 because spam filters at the time where focused on filtering certain keywords, so spammers responded by recreating those words as graphics, which would sail through the filters. Spam filters have since adapted to this technique, but now it's coming back. Why? Hard to say, but my hunch is that so many email messages contain images now -- both commercial and personal -- that unilaterally filtering out image content is no longer an effective strategy. I know when I receive an email that contains mostly hidden images, I almost always choose to "show images" in my email client; there's just no other way to figure out whether it's something useful or not.

The Google/Postini report also offers some other possible explanations, including the likelihood that spammers are "testing" spam filters, or trying out their replacement ISPs with older techniques before advancing on to something more sophisticated.

Another old-school spam technique on the rise: Viruses sent as email attachments. Again, this is an attack that has fallen out of favor in recent years because so many attachments are blocked at the server. Spammers of late have instead sought to direct victims to malicious web links, which are tougher to filter out.

But now virus attachments are making a comeback, another return to the methods that worked in the past. (Though I think these virus attachments will have considerably less success than revisiting image spam techniques.)

All of which just goes to show: Never get complacent when it comes to PC security, because you never know what they're going to try to hit you with.

Top 10 hidden (and not-so-hidden) gems in iPhone Software 3.0

Sure, you already know about cut-and-paste, picture messaging (one AT&T gets around to supporting it, that is) and "Find My iPhone"—but have you heard about the "shake to undo" feature, auto-fill for Safari, and the new way to quit from a frozen app? Get the scoop right here.

We've had iPhone Software 3.0 for almost a day now (there's also a version for the iPod Touch, although it'll cost you $9.95 to download), and all the big new features have been thoroughly poked and prodded by now. Meanwhile, some of the most sought-after features—such as MMS, a.k.a. picture message—and laptop tethering have yet to be supported by AT&T (later this summer, we've been told).

So instead of simply rehashing such features as universal Spotlight search and voice memos (really, Apple, what took you so long?), I've compiled a list of my favorite little features in Software 3.0—along with a couple of bigger ones that I find particularly enticing.

The list isn't meant to be comprehensive—these are just the tips and tricks that I've found most useful so far. Have some that you'd like to share? Then by all means, post them in the comments below for all to see. (For a complete list of new 3.0 features, such as copy-and-paste and universal search, check out Apple's Web site, along with some of my earlier posts here and here.)

And without further ado, here we go…

Call a number directly from a calendar entry
Now, here's an IPhone feature I've really been longing for. If you have an address or phone number in the "Notes" field of a calendar entry, you can now tap them to either map the address or call the number. And if the address and/or phone number isn't getting hotlinked properly, you can always just copy and paste.

Force quit a frozen app
Now you don't have to do a hard reset on your iPhone (performed by pressing and holding the Sleep and Home buttons) if a third-party app goes haywire. Instead, you can just kill the errant process in a couple simple steps. First, press and hold Sleep and Home as if you're doing a hard reset; next, press and hold the Home button. Within a few seconds, you'll be back at the Home screen.

Shake to shuffle or undo
Again, nothing new (especially for owners of some of the newer Sony Ericsson music phones), but cool nonetheless. Listening to a playlist and want to change things up? Just give your iPhone a quick shake; you'll hear a little "beep-bap-boop" sound, and you'll be in shuffle mode. Also: Not thrilled with the sentence you just typed? Shake the phone, and a pop-up will appear, asking whether you'd like to undo your typing.

Log into your YouTube account
Yep, other smartphones have been able to do this for a long time now, but better late than never. Just More and then My Videos or Subscriptions, and you'll be prompted for your YouTube username and password; once that's done, you'll be able to access your clips and subscriptions (natch), rate or comment on videos, subscribe to new channels, and so on.

Compose an email, a text message, or a note with landscape keypad
One of the biggest complaints about the iPhone has finally been fixed—yes, you can now tap on a landscape version of the iPhone's touch keypad from just about any app. Simply turn your handset on its side whenever you're tapping out a new e-mail, SMS, or a sticky, and the landscape keypad will appear.

Auto-fill your info
Shopping on the iPhone just got a lot easier with this 3.0 feature. Tap Settings, Safari, and AutoFill; then, if you want iPhone to automatically fill in Web forms with your contact info, switch the On/Off slider to On and select your own contact card from the address book. You can also set Safari to remember usernames and passwords if you with.

Rent a movie or buy a TV show over Wi-Fi
OK—not exactly a "hidden gem" as 3.0 features go, but as a movie freak I can't resist. At last, you can directly download movie rentals, purchases, or TV episodes over the air; just click on the iTunes app to get started. The bad news is that AT&T's 10MB cap on iTunes downloads over its 3G network still applies, which basically means you'll need Wi-Fi access to grab a 1GB movie rental at the airport. The good news, though, is that all iPhone users get free access to AT&T hotspots, including those at Starbucks—which, as luck would have it, are easy to find at airports. Plan on sipping that latte slowly, however; even over my speedy Wi-Fi connection, it took a good half hour to download a 1.2GB movie like Robert Rodriguez's "Planet Terror." (And yes, you can transfer movie rentals back to your Mac/PC if you wish.)

Keep a closer eye on the market
The iPhone's (Yahoo!-powered) Stocks app gets a bit more useful in Software 3.0. When you tap on a specific ticker symbol, you'll still see the daily, month, or yearly price chart on the bottom half of the screen; now, though, you can swipe it for recent headlines or volume, market cap, 52-week high and low info, and more.

Forward or delete a text message
I've always liked how the iPhone displays SMS conversations in a "threaded" format, but until now, there wasn't a way to forward pithy texts or delete specific messages (besides simply wiping an entire conversation). Now, you can; just tap Edit in an SMS conversation, then select the messages you'd like to forward or zap.

Get "push" notifications
Again, probably not the most "hidden" feature in 3.0, but I like it so much that I'm including it anyway. The iPhone still lacks true multitasking (as found on the Palm Pre), but with "push notification"—new to Software 3.0—developers of third-party apps can "push" alerts, sounds, and icon badges to your phone even when the given app isn't running. For example, the Associated Press app will push you a pop-up window with a sound alert when a bulletin hits the wire (I just got one for a Supreme Court ruling on DNA testing), while Tap Tap Revenge will ping you whenever one of your Tap Tap pals wants to challenge you to an over-the-air duel. (MacRumors has a list ofearly push-supported apps here.) Don't worry—you can configure push notification in the Settings menu, or turn it off entirely if you wish. (Also, keep in mind that turning push notification on may put a dent in your battery life.)

What are your favorite new feature in iPhone Software 3.0? Post 'em below.

Source: Yahoo

Windows XP life extended yet again to (possibly) 2011

Like Michael Corleone in The Godfather Part III, just when you think Windows XP is out... they pull it back in.

Once again -- and I've now lost count on this one -- Microsoft is officially extending the life of the venerable Windows XP operating system. Based on the company's new rules, the OS can be pre-installed on machines for up to 18 months after the general availability of Windows 7 -- or until Windows 7 Service Pack 1 is released, whichever is sooner.

Assuming Windows 7 ships in October as planned, that means XP may be alive and well until April 2011. On the other hand, Microsoft has been releasing Service Packs more quickly of late, and 18 months would be an awfully long time for Windows to go without a patch.

The move was apparently a response to Gartner's Michael Silver, who lambasted the company's previous policy, which would create only six months of overlap between XP and Windows 7, and which he saw as not enough time for large enterprises to manage the transition from one OS to the other. (And let's get real: No one is going to upgrade to Vista in the meantime.)

In response, Silver called the new policy "good" but "still not great."

His beef? Microsoft's Service Pack clause, which is as nebulous a term as one can fathom. Service Packs are really nothing more than bundled up collections of bug fixes, and there are no guidelines about how serious those fixes need to be or how many of them one needs in order to justify putting out a Service Pack of them. Microsoft could release Windows 7 Service Pack 1 a week after it was released -- citing whatever reasons it wanted -- and abruptly yank XP from the market. What's worse is that Service Packs can arrive without much warning, which would give businesses even less time to prepare for XP going off market.

As a side note, remember that XP is already technically at its end of life: It's no longer available at retail, and only extended support plans are available. Technically only businesses are supposed to be able to buy it. Microsoft will stop patching XP, as well, in April 2014 -- and that includes all security updates.

Unless it changes its mind. Again.

source:Yahoo!!!

Is Moore's Law about to die?

It's one of the most famous maxims in the technology world: Moore's Law, originally conceived by Intel's Gordon Moore in 1965, posits that the number of transistors on a circuit will double every 1 1/2 to 2 years. That has held true -- like a rock -- since it was envisioned, from the 2,300 transistors on an Intel 4004 to the 2 billion or so transistors on a quad-core Itanium produced today.

But even Moore has cautioned that the Law won't be sustainable forever. The limits of physics -- the size and characteristics of electrons that have to move through these circuits, for example -- mandate that at some point, we'll either have to stop shrinking transistors (which is how you fit more and more of them on a chip) or move to another form of CPU that doesn't rely on traditional silicon. Either way, Moore's Law would no longer apply. Intel itself has predicted the imminent end of Moore's Law on many occasions, though its most recent prediction is that there is "no end in sight."

Research group iSuppli would beg to differ with that opinion, and says that not only is the end in sight, it's right around the corner: By 2014, the company says Moore's Law will cease to drive chip design, and for a reason unrelated to physics. Rather, it's economics that will kill Moore's Law as we know it.

The big shift comes, says iSuppli, when companies shrink transistor nodes to below 20nm. The problem has nothing to do with the chips themselves, but the equipment that will have to be built in order to make the chips. Since that equipment is really only useful during the lifetime of a single chip generation, it has to be depreciated over the life of that generation. At the 20nm point, equipment "costs will be so high, that the value of their lifetime productivity can never justify it," according to the company.

We still have a bit of time for that economic reality to alter itself. Today, chips utilizing 45nm connectors are standard, with 32nm on the horizon (Intel could have these chips out in 2010), and 22nm the next step after that. 16nm (or possibly 18nm) would mark the following step in the progression, a point at which we'd then be in the world of "nanoelectronics" where individual atoms may have to be manipulated to construct a CPU. And some companies, including Toshiba, already have early production plans announced at this level, though on a limited scale in comparison to Intel.

Given the current state of the tech industry, economic reality is indeed a tough thing to get past, but it would be sad if money alone stopped chip advances dead in their tracks. Anyone want to take up a collection? Save Moore's Law!

source:Yahoo

Today's diet!!

BF:
nothing, woke up late...!! got WILD in dreams :P.. Repaired my bicycle...
Had a head massage, it will be wonderful 4 geeks 2 have massage!

then cycled to office...!

Had LUNCH:
PURI, Mutter masala, chicken soup, Dal, Buttermilk!! Had stomach fulll!!! owehhhhhhhhh!!!!!!!!!!

Abt Padi's testi in orkut!!!

A Classic geek!

An ADOBE lover!!!

A Template monster!!!!

A veteran script kiddie!!

An Orchid7 certified Hacker!!!!!

Our Quest Chief Tech Architet!!!!!!

Digg2Hero Omner!!!!!!!

Only guy in college who tried to install MAC LeopordX(Of course adjusted with theme)!!!


A hip hop raper!!!

A cool Sapper!!!!

Only guy in college who can throw chess ball in cricket!!!!

Co-founder of unknown search engine which uses Suffix arays, works better than google!!! Google utterly failed to get those patents!!! but this fr3ak dont kno Suffixes [:P]

6-packer, hey sorry 12 packer [:P]

Mess topper!!!!!

hez da only person i envy in my class when it comes to geekyness...!!

Hack-in-Hack-out winner!!!!!

A good Skater!!!

hey u kno, this is a smal attempt from me to get a small autograph from him, after few yrs or so.... kidding!!! not exactly....!!!

missing ur slow pysco smile raa!!

Today's diet!!!

BF:
Fruit Salad..!!!
One class Plain milk!!!

Lunch:
Chicken Biryani!!!
3 roti!!
Vanila and chocolate icecream!!
Veg manchuria 4 cups!! :P
Dal, Capsicum Masala, buttermilk!!

Evening at Gym:
burnt 83 Kcal cycling for 15 min!!!
burnt 104 Kcal jogging for 15 min!!!
cardio's for 30 min!!!

Dinner:
1 set dosa....!!
2 spoons puligora(thats how kannada ppl call pulihora).
One apple...!!
carrot and keera!!!!

HorrorScope

Others could be trying to take advantage of your kindness today. Try to find that balance between being generous and being na ve. Your kindness may get you a few points with others, but if you get taken advantage of your mood will certainly be spoiled and your faith in humanity may be questioned!


ha ha ha.... am i kind???? lets C.... balance between generous and naive :-P
I m jus a geek!!!!

Luving Wolfram!!!!

Wonderful knowledge engine!!!!


this answers almost every puzzle or problem!!!
http://www.wolframalpha.com/

ha ha ha...!! getting addicted to it!!!

my craziness:
tried to find out "3+6+9+..................."
Crap isn't it?????


but it answered beautifuly.....

check out ur craziness and get amazed by its interpretation...!!!!!!!!!!

So many flash games!!!!!!!!!!!!!!!!
@
http://www.games68.com


It helped to embed games in my site!!!

TT battle!!

Today played at around 4 games... today i got some nick!! Smashed 4!!

game --- 17,
game --- 16 with kiran

and

game --- 6,
game --- 8 with sunitha.. :)


Jus completed 2 games with Kiran, its 11:20pm now..!!! this is what i call as life in Y!!! Beds to sleep... TV's (54" Bravia) to watch DC vs DD.... Y! rocks!!!! coming to game,
19---Game...!!
game---16!!
game---11!!!


then i played with Anil....
this is game.... ego's inside, displaying game out... fighting to win....!!
finally he won...!!! but i loved the way i fought!! He played wonderfully!!
Its deuce!!!
he won!!!

My first Offer screwed up!!!!

"Capgemini is a leader in consulting, technology and outsourcing services"

????

What da ....????????????????

I thought of this capGemini as a good service based company.... hmm... big big mistake guys...!!

These service based companies sucks!!!

This company came @ around august 2008 for campus recruitment, hired 20 odd students and telling now that it will call around 2nd Quarter of 2010, not even specific about it..!!

capGemini SUCKS!!!!!!!!!!!!!!!!!!!!!!

Thought of it as a good brand!!!

IT SUCKS!!!!!!!!!!!!!!!

Improve your Website page ranking through reciprocal linking!!!

The aim of a reciprocal linking strategy is usually twofold: First to attract visitors from the linking partner to your own site and, secondly, to improve your page ranking with the search engines. A higher page ranking, especially with Google, indicates more relevance when inquiries are made on a given keyword. Relevance encourages the search engines to send free, targeted traffic to your website.


Important Considerations

1. Build online relationships. Exchanging links with other relevant websites is a great way to start building partnerships with other website owners and may open the door for future joint venture requests.

2. Build your link popularity. Most search engines view sites that have many links to them as being important. So, the more sites that link to your site, the higher your site might rank. But again, make sure that all reciprocal links are relevant to your site or the search engines will penalize you.

3. Avoid exchanging links with sites that have a huge link directory. If your site is listed on page 43 in your category of another site's link directory, few people will ever see your link. Although a link will be generated to your site for the search engines, you will not receive much traffic from the link exchange. Try to exchange links with sites where your link will be displayed on the first, or at the most, the second page of another site's link directory.

4. Don't exchange links with everybody that asks. What advantage is there in exchanging links with a site that sells wedding favors when your site is about dog training? Anyone that visits the wedding favor site will be looking for information concerning weddings, not dog training, and very few will click on your link regardless of how high the page rank is for the wedding site. The key here is to exchange links only with sites that are relevant to your site or to your keywords.

5. The main goal of any linking strategy is to get more traffic to a website. Reciprocal linking can work for or against you in this matter depending on the site that you exchange links with. If you exchange links with sites that receive a lot of traffic, some of that traffic may be diverted to your site. On the other hand, if you exchange links with a low traffic site, you may divert some of your traffic to the other site without seeing a similar return. The solution is to exchange reciprocal links with a site with a page rank no lower than one level below yours and to try to exchange links with many sites with a higher page rank. Ideally, you would seek to exchange links with sites that have at least a PR 4.

How To Set Up A Link Page

The optimum way to set up a link page is to enter all links manually. Yes, it is time consuming but when you are starting out, this is the best way to do it.

You would first need to set up a page on your website just for your link categories. You can call this page anything you like such as Links, My Partners, Link Partners, My Link Partners, etc. Set up this page with the major categories and subcategories that are relevant to your site. Then, set up a page for each subcategory that will contain the actual links. Test to be sure that whenever anyone clicks on a subcategory that they are taken to the appropriate link page.

Prepare a short 3 - 5 line ad about your website or your product and include the URL to your website. This should be in HTML code for easy uploading. Each linking company has their own procedure, but generally, each time you ask to exchange links, you'll need to copy and paste the other website's HTML code onto your link page under the correct category and subcategory. You will then need to upload the updated page to your website.

Once this is done, let the other website know on which of your pages they can find their link. If the other website owner approves the link exchange, they should add your link to their link page and inform you on exactly what page you can find it.

Check to make sure that your link has been added to their site. If they have not added your link, you have the option of contacting the website owner as to why or of removing their link from your site.

Mention reciprocal linking on any internet marketing forum and you will be sure to get a barrage of heated replies. There is a continual debate about the advantages and disadvantages involved in reciprocal linking and both sides make convincing statements.

If you do decide to get involved in reciprocal linking, join only well established link exchanges that allow you to approve or disapprove the link. Avoid link farms or link exchanges that will automatically exchange your link with their entire database regardless of the relevancy to your website.

sachin mania

Sachin Tendulkar scored his 42nd Test century and gave Seddon Park a batting masterclass as India established a stranglehold on proceedings on the third day. Having started the day one run in arrears, they piled up 242 in two sessions before dismissing both New Zealand openers and Kyle Mills, the night-watchman, in 31 overs before stumps. With Harbhajan Singh getting sharp turn and Munaf Patel hinting at some reverse swing, New Zealand's prospects of saving the game were decidedly slim.

Tendulkar's hundred took just 168 balls and his positive intent never allowed the bowlers to settle. India lost Yuvraj Singh to an error of judgement but though Mahendra Singh Dhoni was initially subdued, a 115-run partnership gave India an advantage that weren't likely to relinquish.

Over the past few months, there have been several glimpses of the Tendulkar of old, the peerless strokemaker who just came out and played without a thought for the cares of the world. That was in evidence again in the morning, with some magnificent strokes played all around the wicket. The tone for the day was set in the very first over with a lovely cover-drive after Yuvraj had clipped Chris Martin off the pads twice for fours.

In Martin's next over, Tendulkar played a gorgeous back-foot cover-drive, and when Iain O'Brien was glanced and then cut for four, he was into the 90s. The partnership was beginning to look ominous when Martin gave New Zealand some respite. Coming round the wicket, he got the ball to nip back a smidgen off the seam. Yuvraj watched it all the way and just shouldered arms. The ball took off stump.

Dhoni edged the first ball he faced just short of third slip, but all eyes were on Tendulkar. A wonderful stroke through cover off O'Brien took him to 99, and a wristy tuck on to the onside when James Franklin came on to bowl had the crowd on its feet, to acclaim a man whose feats are unlikely ever to be matched.

The punishment was far from over though. Jesse Ryder had been miserly on day two, but 24 hours later, Tendulkar greeted him with an on-drive, a deft swish behind point and a nonchalant clip off the pads. Of the 66 runs scored before drinks, he had made 47.

Dhoni was watchful at the other end, with only a fluent cover-drive off Franklin offering a glimpse of the strokes at his disposal. Daniel Vettori came on and bottled one end up, unlucky perhaps not to get an lbw decision against Tendulkar, but the slumping body language of his team-mates said it all.

It only got worse after lunch. Tendulkar swept Vettori for four and was ruthless in his execution of the cut when Martin dropped short and wide. When he tapped one down to third man, he had his 18th score of 150 or more, and the century partnership came up soon after as Dhoni unleashed a withering off-drive off Martin.

It was the impressive O'Brien that gave his beleaguered team some respite. The third umpire was needed to make sure that Ryder hadn't caught Dhoni at gully after another fierce cut, but India's captain was on his way three balls later after gloving a short-pitched delivery behind. Then, after an immaculate punch down the ground off O'Brien, Tendulkar's 260-ball effort ended with an edge to first slip, after he tried to fend a bouncer down towards fine leg.

By then, the lead was 164 and though Vettori took a smart diving catch at mid-off to end Harbhajan Singh's cameo, there was further punishment from Zaheer Khan, who hit the ball through and over the covers with the ease of a frontline batsman. The hapless Mills went for three fours in an over, and the 500 came up right after Daniel Flynn had put Zaheer down off Franklin's bowling. Zaheer celebrated that chance with two whiplashes through cover, and a risky single soon after gave him 50 from 45 balls and added insult to considerable injury.

Vettori was tidy while O'Brien and Martin toiled hard but the lack of quality from the back-up bowlers was glaring, especially against the tail. There were bound to be changes for Napier, but as they headed for the dressing room after Munaf holed out, all thoughts were on surviving Hamilton.

When New Zealand batted a second time, Tim McIntosh lasted just three balls. There were doubts over whether the edge off Zaheer carried to Tendulkar at first slip and the fielder himself went off with a badly jammed and bleeding finger. Tendulkar later clarified that his finger was sore, but had not been broken. Martin Guptill and Flynn slowly set about building the innings with Guptill playing some glorious strokes through the covers and working the ball neatly off his pads. The shot of his innings was undoubtedly a swivel-pull for six off Ishant Sharma.

All the good work was undone in the final few minutes though. Guptill was just two short of a half-century on debut when he played a lazy drive at Harbhajan for Virender Sehwag to take a tumbling catch at mid-off and Munaf then trapped Mills in front with the last ball of the day. The shouts of celebration reverberated around the ground, and the Indians took their time to walk off after a day when pretty much everything had gone their way.

6yr-old Indian-American boy's IQ is greater than that of Einstein

Chicago, March 13 (ANI): An Indian-American boy has an IQ greater than that of Albert Einstein at the tender age of six.

Pranav Veera has an IQ of 176, while Einstein's IQ was believed to be about 160.

The little boy can recite the names of the U.S. presidents in the order they served in office, and is able to say the alphabet backward.

Given a date back to 2000, Pranav can even tell which day of the week that was.

He is highly competitive at playing Wii video games, and likes to play outside.

Pranav's parents have revealed that he seemed unusually intelligent while playing with alphabet sets, when the boy was just four-and-a-half years old.

He could even recall which letters were certain colours, they say.

"That kind of puzzled us. You have to have not a normal memorization, but some other means of recall," the Chicago Sun-Times quoted his father Prasad Veera as saying.

The little boy's mother, Suchitra Veera, has revealed that he presently loves all kinds of alphabets.

"He loves to collect them, like different colors, different sizes, different materials," she said.

Pranav's parents decided to have his IQ tested at Powers Educational Services in Hyde Park three months ago

"I said, 'Let's try it out, because he seems to do a lot of stuff kind of not quite normal for his age. He tested 176," his father said.

Pranav's teacher Marci Taylor, at McCormick Elementary in the Milford School District, calls him "an amazing child".

"He knows so much, yet he's probably more excited about learning than any child I've ever seen. He shakes with excitement," she said.

What she finds impressive about Pranav is the fact that he knows so many incredible things at the age of 6.

"He loves to go play at recess and climb on the monkey bars," Taylor said.

When asked what he wants to be when he grows up, Pranav says: "An astronaut." (ANI)



source:ANI

Improve Your site performance

Minimize HTTP Requests

tag: content

80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.

One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.

Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.

CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.

Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it's not recommended.

Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.

Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer's blog post Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.

top | discuss this rule

Use a Content Delivery Network

tag: server

The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective. But where should you start?

As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.

Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This not only achieves a bigger reduction in response times, but it's easier thanks to content delivery networks.

A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.

Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, Mirror Image Internet, or Limelight Networks. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.

top | discuss this rule

Add an Expires or a Cache-Control Header

tag: server

There are two things in this rule:

• For static components: implement "Never expire" policy by setting far future Expires header


• For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests

Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used on all components including scripts, stylesheets, and Flash components.

Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.

      Expires: Thu, 15 Apr 2010 20:00:00 GMT

If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.

      ExpiresDefault "access plus 10 years"

Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js.

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user's Internet connection.

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Gzip Components

tag: server

The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It's true that the end-user's bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.

Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.

      Accept-Encoding: gzip, deflate

If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.

      Content-Encoding: gzip

Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you're likely to see is deflate, but it's less effective and less popular.

Gzipping generally reduces the response size by about 70%. Approximately 90% of today's Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.

There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.

Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It's also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it's worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.

Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.

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Put Stylesheets at the Top

tag: css

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.

Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.

The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.

The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: "Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times." Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.

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Put Scripts at the Bottom

tag: javascript

The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames.

In some situations it's not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page's content, it can't be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.

An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn't support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.

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Avoid CSS Expressions

tag: css

CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They're supported in Internet Explorer, starting with version 5. As an example, the background color could be set to alternate every hour using CSS expressions.

      background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );

As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.

The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.

One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.

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Make JavaScript and CSS External

tag: javascript, css

Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?

Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.

The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.

Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!'s front page and My Yahoo!.
Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.

For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser's cache.

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Reduce DNS Lookups

tag: content

The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.

DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record.

Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeout registry setting. Firefox caches DNS lookups for 1 minute, controlled by the network.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)

When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page's URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.

Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.

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Minify JavaScript and CSS

tag: javascript, css

Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI Compressor. The YUI compressor can also minify CSS.

Obfuscation is an alternative optimization that can be applied to source code. It's more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.

In addition to minifying external scripts and styles, inlined <script> and <style> blocks can and should also be minified. Even if you gzip your scripts and styles, minifying them will still reduce the size by 5% or more. As the use and size of JavaScript and CSS increases, so will the savings gained by minifying your code.

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Avoid Redirects

tag: content

Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:

      HTTP/1.1 301 Moved Permanently
      Location: http://example.com/newuri
      Content-Type: text/html

The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control, indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.

The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.

One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite, or the DirectorySlash directive if you're using Apache handlers.

Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite.

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Remove Duplicate Scripts

tag: javascript

It hurts performance to include the same JavaScript file twice in one page. This isn't as unusual as you might think. A review of the ten top U.S. web sites shows that two of them contain a duplicated script. Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts. When it does happen, duplicate scripts hurt performance by creating unnecessary HTTP requests and wasted JavaScript execution.

Unnecessary HTTP requests happen in Internet Explorer, but not in Firefox. In Internet Explorer, if an external script is included twice and is not cacheable, it generates two HTTP requests during page loading. Even if the script is cacheable, extra HTTP requests occur when the user reloads the page.

In addition to generating wasteful HTTP requests, time is wasted evaluating the script multiple times. This redundant JavaScript execution happens in both Firefox and Internet Explorer, regardless of whether the script is cacheable.

One way to avoid accidentally including the same script twice is to implement a script management module in your templating system. The typical way to include a script is to use the SCRIPT tag in your HTML page.

      <script type="text/javascript" src="menu_1.0.17.js"></script>

An alternative in PHP would be to create a function called insertScript.

      <?php insertScript("menu.js") ?>

In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.

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Configure ETags

tag: server

Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.

      HTTP/1.1 200 OK
      Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
      ETag: "10c24bc-4ab-457e1c1f"
      Content-Length: 12195

Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.

      GET /i/yahoo.gif HTTP/1.1
      Host: us.yimg.com
      If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
      If-None-Match: "10c24bc-4ab-457e1c1f"
      HTTP/1.1 304 Not Modified

The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.

The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.

IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS is Filetimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS servers behind a web site.

The end result is ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn't a problem. But if you have multiple servers hosting your web site, and you're using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you're consuming greater bandwidth, and proxies aren't caching your content efficiently. Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.

If you're not taking advantage of the flexible validation model that ETags provide, it's better to just remove the ETag altogether. The Last-Modified header validates based on the component's timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:

      FileETag none

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Make Ajax Cacheable

tag: content

One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won't be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It's important to remember that "asynchronous" does not imply "instantaneous".

To improve performance, it's important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:

• Gzip Components
  
  
  
• Reduce DNS Lookups
  
  
• Minify JavaScript
  
  
• Avoid Redirects
  
  
• Configure ETags
  
  

Let's look at an example. A Web 2.0 email client might use Ajax to download the user's address book for autocompletion. If the user hasn't modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn't been modified since the last download, the timestamp will be the same and the address book will be read from the browser's cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn't match the cached response, and the browser will request the updated address book entries.

Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.

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Flush the Buffer Early

tag: server

When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page.
During this time, the browser is idle as it waits for the data to arrive.
In PHP you have the function flush().
It allows you to send your partially ready HTML response to the browser so that
the browser can start fetching components while your backend is busy with the rest of the HTML page.
The benefit is mainly seen on busy backends or light frontends.

A good place to consider flushing is right after the HEAD because the HTML for the head is
usually easier to produce and it allows you to include any CSS and JavaScript
files for the browser to start fetching in parallel while the backend is still processing.

Example:

      ... <!-- css, js -->
    </head>
    <?php flush(); ?>
    <body>
      ... <!-- content -->

Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.

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Use GET for AJAX Requests

tag: server

The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process:
sending the headers first, then sending data. So it's best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies).
The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.

An interesting side affect is that POST without actually posting any data behaves like GET.
Based on the HTTP specs, GET is meant for retrieving information, so it
makes sense (semantically) to use GET when you're only requesting data, as opposed to sending data to be stored server-side.

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Post-load Components

tag: content

You can take a closer look at your page and ask yourself: "What's absolutely required in order to render the page initially?".
The rest of the content and components can wait.

JavaScript is an ideal candidate for splitting before and after the onload event. For example
if you have JavaScript code and libraries that do drag and drop and animations, those can wait,
because dragging elements on the page comes after the initial rendering.
Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.

Tools to help you out in your effort: YUI Image Loader allows you to delay images
below the fold and the YUI Get utility is an easy way to include JS and CSS on the fly.
For an example in the wild take a look at Yahoo! Home Page with Firebug's Net Panel turned on.

It's good when the performance goals are inline with other
web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can
improve the user experience but you have to make sure the page works even without JavaScript. So after you've made sure the page
works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.

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Preload Components

tag: content

Preload may look like the opposite of post-load, but it actually has a different goal.
By preloading components you can take advantage of the time the browser is idle and request components
(like images, styles and scripts) you'll need in the future.
This way when the user visits the next page, you could have most of the components already in
the cache and your page will load much faster for the user.

There are actually several types of preloading:

• Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components.
  Check google.com for an example of how a sprite image is requested onload. This sprite image is
  not needed on the google.com homepage, but it is needed on the consecutive search result page.


• Conditional preload - based on a user action you make an educated guess where the user is headed next and preload accordingly.
  On search.yahoo.com you can see how some extra components are requested
  after you start typing in the input box.


• Anticipated preload - preload in advance before launching a redesign. It often happens after a redesign that you hear:
  "The new site is cool, but it's slower than before". Part of the problem could be that the users were visiting your old site with a
  full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some
  components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts
  that will be used by the new site

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Reduce the Number of DOM Elements

tag: content

A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference
if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.

A high number of DOM elements can be a symptom that there's something that should be improved with the markup
of the page without necessarily removing content.
Are you using nested tables for layout purposes?
Are you throwing in more <div>s only to fix layout issues?
Maybe there's a better and more semantically correct way to do your markup.

A great help with layouts are the YUI CSS utilities:
grids.css can help you with the overall layout, fonts.css and reset.css
can help you strip away the browser's defaults formatting.
This is a chance to start fresh and think about your markup,
for example use <div>s only when it makes sense semantically, and not because it renders a new line.

The number of DOM elements is easy to test, just type in Firebug's console:


document.getElementsByTagName('*').length

And how many DOM elements are too many? Check other similar pages that have good markup.
For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).

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Split Components Across Domains

tag: content

Splitting components allows you to maximize parallel downloads. Make sure you're using
not more than 2-4 domains because of the DNS lookup penalty.
For example, you can host your HTML and dynamic content
on www.example.org
and split static components between static1.example.org and static2.example.org

For more information check
"Maximizing Parallel Downloads in the Carpool Lane" by Tenni Theurer and Patty Chi.

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Minimize the Number of iframes

tag: content

Iframes allow an HTML document to be inserted in the parent document.
It's important to understand how iframes work so they can be used effectively.

<iframe> pros:

• Helps with slow third-party content like badges and ads


• Security sandbox



• Download scripts in parallel

<iframe> cons:

• Costly even if blank


• Blocks page onload



• Non-semantic

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No 404s

tag: content

HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found)
is totally unnecessary and will slow down the user experience without any benefit.

Some sites have helpful 404s "Did you mean X?", which is great for the user
experience but also wastes server resources (like database, etc).
Particularly bad is when the link to an external JavaScript is wrong and the result is a 404.
First, this download will block parallel downloads. Next the browser may try to parse
the 404 response body as if it were JavaScript code, trying to find something usable in it.

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Reduce Cookie Size

tag: cookie

HTTP cookies are used for a variety of reasons such as authentication and personalization.
Information about cookies is exchanged in the HTTP headers between web servers and browsers.
It's important to keep the size of cookies as low as possible to minimize the impact on the user's response time.

For more information check
"When the Cookie Crumbles" by Tenni Theurer and Patty Chi.
The take-home of this research:

• Eliminate unnecessary cookies


• Keep cookie sizes as low as possible to minimize the impact on the user response time


• Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected


• Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time

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Use Cookie-free Domains for Components

tag: cookie

When the browser makes a request for a static image and sends cookies together with the request,
the server doesn't have any use for those cookies. So they only create network traffic for no good
reason. You should make sure static components are requested with cookie-free requests. Create
a subdomain and host all your static components there.

If your domain is www.example.org, you can host your static components
on static.example.org. However, if you've already set cookies on the top-level domain
example.org as opposed to www.example.org, then all the requests to
static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static
components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com,
Amazon uses images-amazon.com and so on.

Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache
the components that are requested with cookies.
On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact.
Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the
www subdomain and
write the cookies to that subdomain.

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Minimize DOM Access

tag: javascript

Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:

• Cache references to accessed elements


• Update nodes "offline" and then add them to the tree


• Avoid fixing layout with JavaScript

For more information check the YUI theatre's
"High Performance Ajax Applications"

by Julien Lecomte.

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Develop Smart Event Handlers

tag: javascript

Sometimes pages feel less responsive because of too many event handlers attached to different
elements of the DOM tree which are then executed too often. That's why using event delegation is a good approach.
If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of
one handler for each button. Events bubble up so you'll be able to catch the event and figure out which button it originated from.

You also don't need to wait for the onload event in order to start doing something with the DOM tree.
Often all you need is the element you want to access to be available in the tree. You don't have to wait for all images to be downloaded.

DOMContentLoaded is the event you might consider using instead of onload, but until it's available in all browsers, you
can use the YUI Event utility, which has an onAvailable method.

For more information check the YUI theatre's
"High Performance Ajax Applications"

by Julien Lecomte.

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Choose <link> over @import

tag: css

One of the previous best practices states that CSS should be at the top in order to allow for
progressive rendering.

In IE @import behaves the same as using <link> at the bottom of the page, so it's best not to use it.

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Avoid Filters

tag: css

The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7.
The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded.
It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.

The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE.
If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.

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Optimize Images

tag: images

After a designer is done with creating the images for your web page, there are still some things you can try before you
FTP those images to your web server.

• You can check the GIFs and see if they are using a palette size corresponding
  to the number of colors in the image. Using imagemagick it's easy to check using
  
  
  identify -verbose image.gif
  
  
  
  When you see an image useing 4 colors and a 256 color "slots" in the palette, there is room for improvement.
  


• 
  Try converting GIFs to PNGs and see if there is a saving. More often than not, there is.
  Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past.
  The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don't
  support variable transparency either.
  So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations).
  This simple imagemagick command results in totally safe-to-use
  PNGs:
  
  convert image.gif image.png
  
  
  "All we are saying is: Give PiNG a Chance!"
  



• 
  Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:
  
  
  pngcrush image.png -rem alla -reduce -brute result.png
  


• 
  Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize
  and remove comments and other useless information (such as EXIF information) from your images.
  
  
  
  jpegtran -copy none -optimize -perfect src.jpg dest.jpg
  

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Optimize CSS Sprites

tag: images

• Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.


• Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.


• "Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much
  but requires less memory for the user agent to decompress the image into a pixel map.
  100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels
  

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Don't Scale Images in HTML

tag: images

Don't use a bigger image than you need just because you can set the width and height in HTML.
If you need

<img width="100" height="100" src="mycat.jpg" alt="My Cat" />


then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.

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Make favicon.ico Small and Cacheable

tag: images

The favicon.ico is an image that stays in the root of your server.
It's a necessary evil because even if you don't care about it the
browser will still request it, so it's better not to respond with a 404 Not Found.
Also since it's on the same server, cookies are sent every time it's requested.
This image also interferes with the download sequence, for example in IE when you request
extra components in the onload, the favicon will be downloaded before these extra components.

So to mitigate the drawbacks of having a favicon.ico make sure:

• It's small, preferably under 1K.


• Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it).
  You can probably safely set the Expires header a few months in the future.
  You can check the last modified date of your current favicon.ico to make an informed decision.
  

Imagemagick can help you create small favicons

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Keep Components under 25K

tag: mobile

This restriction is related to the fact that iPhone won't cache components bigger than 25K.
Note that this is the uncompressed size. This is where minification is important
because gzip alone may not be sufficient.

For more information check "Performance Research, Part 5: iPhone Cacheability - Making it Stick" by Wayne Shea and Tenni Theurer.

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Pack Components into a Multipart Document

tag: mobile

Packing components into a multipart document is like an email with attachments,
it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive).
When you use this technique, first check if the user agent supports it (iPhone does not).

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