Causes for websites slow?

1. A client first needs to determine the IP address and port number of the web server from the URI. If the hostname in the URI was not recently visited, it may take tens of seconds to convert the hostname from a URI into an IP address using the DNS resolution infrastructure.

 Luckily, most HTTP clients keep a small DNS cache of IP addresses for recently accessed sites. When the IP address is already "cached" (recorded) locally, the lookup is instantaneous. Because most web browsing is to a small number of popular sites, hostnames usually are resolved very quickly.

2. Next, the client sends a TCP connection request to the server and waits for the server to send back a connection acceptance reply. Connection setup delay occurs for every new TCP connection. This usually takes at most a second or two, but it can add up quickly when hundreds of HTTP transactions are made.

3. Once the connection is established, the client sends the HTTP request over the newly established TCP pipe. The web server reads the request message from the TCP connection as the data arrives and processes the request. It takes time for the request message to travel over the Internet and get processed by the server.

4. The web server then writes back the HTTP response, which also takes time.

The magnitude of these TCP network delays depends on hardware speed, the load of the network and server, the size of the request and response messages, and the distance between client and server. The delays also are significantly affected by technical intricacies of the TCP protocol.