IBM 3270 Manual page 14

Three things will happen:
1.
The memory in your system is checked and
the amount that is working appears in the
upper left corner of your screen.
I
""0
KB OK
Note: This number increases until it equals
the amount of available storage in your
system unit.
2.
You will hear
1
short "beep".
You may also hear the diskette reader hum
and see the red "in use" lights flicker on and
off.
Chapter
1.
Turning on PC/Loading Control Program 1-3