IBM 5150 Manual To Operations page 129

Remember, if the information is moving too fast for you
to read it, press and hold the Ctrl key and then press the
Num Lock key. Then press another key when you're
done reading to start displaying again. It is also a good
idea to print a copy of a diskette's directory (Ctrl
+
Prtsc) to keep with the diskette.
6
When all the files have been installed, the DOS prompt
appears: A>
With Two Drives
If you have two diskette drives, you can keep the DOS
Diskette in drive A:, if it is there, and insert your diskette
into drive B:. Then at step 4, type this:
dir b:
and press the Enter key.
You have to tell DOS where to find the diskette-in this
case the one in drive B:. Otherwise, DOS assumes you
mean the default drive diskette if you type only the
command (dir) without a drive specifier.
DOS 3-55