Here's one more good from the fine folks @ O' Reilly:
HTTP Request Types
The request type is passed by the client to the server to indicate what the server should do with the URL that's also supplied by the browser. Although the HTTP specification details a number of request types, like PUT and DELETE, only two are supported by all servers and in common use: GET and POST. A GET request asks the server to "get" a piece of information, typically a document, and return it to the client. If the request includes any additional information, these are appended as arguments to the URL. A POST request, on the other hand, provides the server with information to be "posted" to the URL; typically, it's used to send the contents of an HTML form to the server, or to provide the server with information that's needed for back-end processing. The information itself is contained in the body of the request.
Most servers cannot handle data received from either the POST or GET methods internally. Normally, POST requests, as well as GET requests that also send data to the server, are handled by accessory programs or DLLs (CGI and ISAPI applications and ISAPI filters). Both POST and GET requests can return any kind of data of any size.
While it may seem when transmitting data to a web server that GET and POST are similar, one rule is hard and fast: A GET request must never change anything. Don't write an ASP script that makes changes to a database, for instance, in response to a GET request. The reason for this is discussed in greater detail in the following section, "Form Submission."
GET Versus POST
In the event that you're confused about the difference between these two methods, GET can be used to retrieve any document, POST cannot. On the other hand, both GET and POST can be used to pass data to the object indicated by the URL. When GET is used for this purpose, the data is included in the URL as the argument string; in order to extract this data with Win-CGI, you have to parse the argument string. When POST is used, the data is passed to the server in the body of the request message. So, in cases in which data is sent to the server, GET and POST differ in the method used to transmit that data.
Form Submission
A user enters input into the fields of a form. When the form is submitted, the data contained in each field of the form is transferred to the server, which then passes it to ASP. This data is sent in the format name=value, where name is the name assigned to the field by the NAME= attribute of the <INPUT> tag, and value is the value entered in that field. For example, if the user enters "Archie" in a field prompting for his first name, the browser may send along the string first_name=Archie.
If the form is written to use METHOD=GET, the form data is appended to the URL as an argument string. If the form contains many fields or if fields contain long strings of text, the complete URL can become very large and unwieldy. In addition, the limit of the number of characters submitted in a GET--typically about 2000--is much lower than in a POST.
If the form instead uses METHOD=POST, the name=value pairs are sent as the body of the request instead of being appended to the URL. In addition to the greater ease of handling of POST requests, most servers offer better performance when extracting data from the body of a request than from a URL in the request header.
Always use the POST method with forms that change something or cause any irreversible action (most do). POST is safer and more efficient; GET should never be used to change anything. In developing your ASP scripts, you can decide whether you want to support data passed to your program using the GET method.
member of the Request Object.
