This document discusses architectural considerations for AJAX applications. It covers key topics like browser anatomy, HTTP protocols, caching, state handling, and rendering. Browsers limit connections to 4 per domain by default, so domain sharding can help utilize more connections. Caching is important on both the client and server sides. State can be stored in HTTP sessions on the server, cookies on the client, or by keeping state on the rich client with AJAX. Rendering impacts performance, so minimizing reflows during asynchronous rendering is important.