MEM [/CLASSIFY | /DEBUG | /FREE | /MODULE modulename] [/PAGE]

  /CLASSIFY or /C  Classifies programs by memory usage. Lists the size
                   of programs, provides a summary of memory in use, and
                   lists largest memory block available.
  /DEBUG or /D     Displays status of all modules in memory, internal
                   drivers, and other information.
  /FREE or /F      Displays information about the amount of free memory
                   left in both conventional and upper memory.
  /MODULE or /M    Displays a detailed listing of a module's memory use.
                   This option must be followed by the name of a module,
                   optionally separated from /M by a colon.
  /PAGE or /P      Pauses after each screenful of information.

Displays the amount of used and free memory in your system.

TIP: The most helpful options for this command are the /c and /p parameters.

The /p parameter prevents the information from scrolling off the screen before you can read it.

The /c parameter will show you all the TSR (terminate & stay resident) programs currently loaded into conventional (0k - 640k) and upper (640k - 1meg) memory and the amount of space each one uses. It then lists a summary of conventional, extended (XMS) and expanded (if EMM386.SYS specifies RAM; See Configuration) memory used and free.

Now you know what is loaded into your system memory, where it is, the space used, and the free memory totals.

What good is all this information? . . . Here's an example.

You just brought home a new game that advertises great graphics, but when you go to run the program, you get a message:

You say:

"But I have 16meg of memory!!...What's wrong with this program??".

Well, you are right, you do have plenty of memory. But nothing is wrong with the program!

Here's the clue: What type of memory is the program looking for?
Extended (above 640k)? . . . NOPE!
It wants more of your conventional (0-640k) memory!

Option 1 is read the manual that came with the game. The designers of the software are the best source for information to get the program to operate on your system.
They will probably suggest a bootdisk solution. This is the simplest answer in many cases.

Option 2 is to alter your startup files, using the information from the mem/c/p command. By loading only the devices you need to run the program, you can free more conventional memory. Also by experimenting with the order in which commands are loaded, you may be able to tweak a bit more free space.(See Configuration)