Web Presentation Guide 5.1
Performance

Action
Design pages that load quickly and reliably.

Why
Users prefer not to wait more than a few seconds to receive the information they are looking for. The longer it takes for a page to load, the more likely it is that the user will cancel the request for that page.

What/How
Web performance is most commonly interpreted as the time it takes a page to fully load. A page load time of 10 seconds or less over a 56kbps modem is an indicator of good performance, and will provide an acceptable user experience even with slower Internet connections.

The most important issue in response time is providing the user an entire screen of useful information. A user may find it acceptable for some page elements to take longer to load if the majority of page content is useful.

Consider the following factors that affect response time:

• Browsers, operating systems, and connection speeds
• Proper execution of all client-side script (e.g. JavaScript) in the various browser types and versions.
• The time a server takes for a "Round-trip" (to the server and back to the browser) for information and data
• Image size and quantity
  • Are images necessary or can text-only links be used instead?
  • Are all images in a standard compressed Web format (e.g. jpg, gif)?
  • Are the image file sizes as small as possible?
• Concurrent users that are likely to request the page during peak and normal usage times

Checklist: Performance

Topic		Complete
a.	Check the download time for the completed page as estimated by the Web-design tool or an online performance analyzer (see the Resources section).
b.	Limit the use of graphics - use multiple occurrences of the same image instead of different images. The image file will be in the user's local cache and will render quickly.
c.	Keep graphics files as small as possible without incurring unacceptable loss to image quality. Always use one of the standard Web formats for images (e.g. .jpg or .gif) and optimize the file size for the Web.
d.	Remember that every distinct graphic element (including rollover images) must be loaded the first time that a visitor hits the page.
e.	Use multimedia effects (e.g. Flash) only when they add to the user's understanding of the information.
f.	Help users predict response time in downloading large pages or multimedia files by indicating the file size of the download next to the link. Indicate sizes (in kb) for any files larger than 50kb.
g.	Use ALT text attributes for images for Accessibility for individuals with disabilities and usability for slow loading pages.
h.	Include WIDTH and HEIGHT attributes on all images and tables so the browser can draw the page quickly.
i.	Make the top of the page meaningful even when no images have been downloaded.
j.	Reduce the complexity of tables as much as possible.
k.	Ensure that the relevant network infrastructure and server hardware is adequate to support the number of visitors to your site.

Resources

Load and Performance Test Tools	Open Source tools to define test cases in XML files, load test HTTP requests, and more
WebPerformance Library	Various links to sites related to Website performance
Performance Testing Tools	Open source test tools and news for performance and other types of testing
Website Performance Books
Speed Up Your Site: Web Site Optimization by Andrew King
Web Performance Tuning, 2nd. Edition By Patrick Killelea

Related guide topics

• Accessibility
• Browser Compatibility
• Hardware and Software Requirements
• Navigation
• PDFs
• Test User Environment
• Usability
• Image Design