IBM 5150 Manual To Operations page 79

Starting DOS
You will usually want to start DOS whenever you start
your computer. For example, you must have DOS
"loaded" before you can start Disk BASIC or Advanced
BASIC programs.
Starting
DOS or
loading
DOS means that a copy of the
DOS programs are read from the DOS Diskette and
placed in the computer's memory. Once the computer
finishes its usual self-checks, you will hear the diskette
drive whirring and clicking while the DOS programs
are being read and transferred to memory.
DOS tells you it is ready when it asks you for the
current date. After that, DOS is ready for you to type
a
command~that
is, to tell DOS what you want it to do.
Let's look at starting DOS, step-by-step.
There are two ways to start DOS, depending on
whether your computer is off or on.
If Your Computer Is Off
1
Insert the DOS Diskette into drive A: and close the
diskette drive cover.
DOS Diskette
2
Turn on the printer, if you have one, a video monitor
or TV, and then the computer.
3
There will be a pause (from 3 to 45 seconds) while the
system checks itself out. Then you will hear the diskette
drive clicking while DOS is being read and transferred.
DOS 3-5