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FDO Tutorial: Lesson 1
by Tau

FDO stands for Form Definition Order. FDO is the programming language in which AOL communicates. This site focuces on the 1991 version of FDO, appropriately called FDO91 which is still used today.


Want to see what FDO streams look like? By the way, an FDO stream is a set of FDO coding. To do this the Star Tool needs to be installed on your computer. The Star Tool, also know as Master AOL, is a tool used by AOL developers to test features still being made. We will utilize its FDO features.

  1. Once the Star Tool is installed, click the "*" menu and go to "Atomic Debugger". This program allows you to view the FDO streams being sent and received by the AOL client. America Online 5.0's Atomic Debugger is pictured below.

  2. Click Setup Options > Setup (Ctrl + Enter).
  3. To turn the Atomic Debugger on, check the box entitled "Atom Trace" in the "Settings" window. The Atomic Debugger will now be on.
  4. Close the "Settings" windows and minimize the Atomic Debugger.
  5. Next, go in AOL and click around, enter a chat room, open your Buddy List, do anything that brings up new windows. Now go back to the Atomic Debugger.
  6. Before looking at the code go back to the "Settings" window and uncheck the "Atom Trace" box.
  7. Now you can go and look at the code. Do not be overwhelmed by the surfeit of code.

If you still want to learn more, procede on.


The areas below in red are atoms.

man_start_object <trigger, "Welcome">
<"f1", 32-30>

man_end_object is working to compile a full database with the function of every atom (there are over 1800). FDO tutorials are unheard of. I have heard rumors that very few people at AOL have the FDO91 Manual. I will pay money for any professionally written, extensive, and full tutorial. Name your price.


AOL also communicates using tokens. Tokens have two parts. First, is a two character category which is also called a token. Second, is an argument which can be one of the three following types:

  • Value: The argument is a number. A detailed explanation of values can be found at BMB's Arguments Tutorial. These are usually used to open new windows.
  • String: The argument is a string. For those that don't know, a string can be considered the same as what we call sentences. These are used when the user sets the string to be sent.
  • Raw: Nothing is sent with the token. Ususally opens a window.

Every window fits into a catagory. For example, most windows that you are probably accostumed to seeing are f1 tokens. These are also know as invokes. These are also easiest for you to access. To get to f1 tokens you need to have the Star Tool installed on AOL. Once you have that installed click the Star Menu, "*", then go to Database... > Invoke Database Record. It looks as follows.

| Documents | Tools | FDO | Atoms | Tokens | Security Breaches

2000 BMB and Tau Productions. Contacts: BMB | Tau | Rob