What's the difference between COMMAND.COM and CMD.EXE?

My advice is simple: forget about COMMAND.COM. It has a long, and venerable
history, but for most practical purposes, it’s no longer needed.

Understanding why is a trip down memory lane for MS-DOS and Windows.

As you probably know, MS-DOS was the predecessor to Windows. It was
character mode only, and you ran programs by typing their name at the command
prompt. MS-DOS was created when 16 bit processors were becoming popular, and
its widespread adoption is credited with kick starting the rise in popularity
of the personal computer.

Then two things happened: Windows, and 32 bit processors. Fast forward to
today, and MS-DOS has pretty much disappeared from the landscape – Windows, and
its rich graphical interface, is everywhere. The same is true for the 16bit
processor. Most all contemporary machines are built on various flavors of 32bit
processors.

What does all that have to do with COMMAND.COM and CMD.EXE? It’s quite
simple really: CMD.EXE is a command line processor for 32bit Windows. Much like
MS-DOS before it, it provides a character-mode only user interface into which
you can type commands to run programs. CMD.EXE is a 32 bit program that is
fully a part of Windows – in fact it’s what gets run when you select
Command Prompt on the Windows Accessories menu.

COMMAND.COM, on the other hand, exists only for compatibility and 16bit
programs. It exists solely for those programs which have not been updated since
the days of MS-DOS. It’s designed to run 16bit applications, and operates just
like the old MS-DOS did.

On the surface, they’re very similar. Even though CMD.EXE was a complete
re-write, it’s based on the same concepts and similar syntax. But the
differences become quickly apparent. Let’s used your “CD” example from
above.

In CMD.EXE, you can change to the “Program files” directory by doing
this:

cd "\Program Files"

Note the quotes around the directory name. Try doing that in COMMAND.COM and
you’ll get this:

cd "\Program Files"
Parameter format not correct -  "\program

The problem is COMMAND.COM doesn’t know about long file names (filenames
longer than 8.3) or filenames that have spaces in them, and it doesn’t have a
way to quote the name. So if you still need to, how do you CD to that directory
in COMMAND.COM? Well, first you need to find out the alternate, 8.3 name of
that directory … its short name:

dir /x
 Directory of C:\
08/21/2005  09:50 AM    <DIR>          PROGRA~1     Program Files

(I’ve removed some of the lines of output for brevity.) The “/X” parameter
to DIR tells it to include the “shortname” in the output. In this case that’s
“PROGRA~1”, a machine generated alternative name for “PROGRAM FILES”. Now we
can CD to that in COMMAND.COM:

cd progra~1
dir
 Volume in drive C is
 Volume Serial Number is B026-62CA
 Directory of C:\PROGRA~1
08/21/2005  09:50 AM    <DIR>          .
08/21/2005  09:50 AM    <DIR>          ..
03/24/2005  04:42 PM    <DIR>          Adobe
...etc...

The bottom line is actually quite simple: use CMD.EXE unless you know you
need COMMAND.COM for compatibility with some older 16bit program. And even
then, if you try and run a 16 bit program in CMD.EXE, it will typically run it
within COMMAND.COM for you anyway, so you still may not need to know or
care.

And in case you’re wondering, yes … something similar is coming down the
road as 64 bit processors begin to arrive. The 64bit version of Windows does, I
believe, include another command processor, one for native 64bit command-line
programs.