No 404s
How minimizing the Number of iframes improves Web site download performance
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.
Other Topics
Overview Web Site performance Improvement Minimize HTTP Requests Use a Content Delivery Network Add an Expires or a Cache-Control Header Gzip Components Put Stylesheets at the Top Put Scripts at the Bottom Avoid CSS Expressions Make JavaScript and CSS External Reduce DNS Lookups Minify JavaScript and CSS Avoid Redirects. Remove Duplicate Scripts Configure ETags Make Ajax Cacheable Flush the Buffer Early Use GET for AJAX Requests Post-load Components Preload Components Reduce DOM Elements Split Components Across Domains Minimize the Number of iframes No 404s Reduce Cookie Size Use Cookie-free Domains for Components Minimize DOM Access Develop Smart Event Handlers Choose over @import Avoid Filters Optimize Images Optimize CSS Sprites Don't Scale Images in HTML Make favicon.ico Small and Cacheable Keep Components under 25K Pack Components into a Multipart Document Avoid Empty Image src
