Initial program loading (IPL) is provided for the ini
tiation of processing when the contents of storage or
Initial program loading is initiated manually by se
lecting an input device with the load-unit switches
and subsequently pressing the load key. When the
multisystem feature is installed, initial program load
ing may be initiated electronically by a signal received
on one of the
Depressing the load key causes a system reset, turns
on the load light, turns off the manual light, sets the
prefix trigger (if present), and subsequently initiates
a read operation from the selected input device.
When reading is completed satisfactorily, a new psw
is obtained, the
light is turned off.
When a signal is received on one of the
the same sequence of events takes place, except that
the read operation is omitted.
System reset suspends all instruction processing, in
terruptions, and timer updating and also resets all
channels, on-line nonshared control units, and
vices. The contents of general and floating-point regis
ters remain unchanged, except that the reset proce
dure may introduce correct parity.
The prefix trigger is set after system reset. In man
state of the prefix-select key switch. When
ated by a signal on one of the two
trigger is set according to the identity of each line.
The prefix trigger is part of the multisystem feature.
starts reading. The first 24 bytes read are placed
in storage locations
gram-controlled interruption, and a possible incor
rect length indication are ignored. The double-word
read into location 8 is used as the channel command
word (ccw) for a subsequent input command. When
chaining is specified in this ccw, the operation pro
ceeds with the ccw in location 16.
After the input operation is performed, the
dress is stored in bits 21-31 of the first word in storage.
The input operation and the storing of the
are not performed when
the new psw. The load light is turned off. When the
Initial program loading resembles a
switches and a zero protection key. The ccw for this
byte count of 24, command-chain flag on, suppress
length-indication flag on, program-controlled-inter
ruption flag off, and a virtual command address of
Initial program loading reads new information into
the first six words of storage. Since the remainder of
of storage, it is possible to preserve such areas of stor
age as the timer and psw locations, which may be
helpful in program debugging.
If the selected input device is a disk, the
mation is read from track
channel adapter involving two cpu's. A system reset
on this adapter causes an attention signal to be sent
to the addressed
write command necessary to load a program into main
storage of the requesting
(the manual, the system, and the load lights are
Operator Control Section
This section of the system control panel contains only
the controls required by the operator when the
pervisor control, a minimum of direct manual inter
vention is required since the supervisor performs
operations like store and display.
The main functions provided by the operator con
trol section are the control and indication of power,
the indication of system status, operator to machine
communication, and initial program loading.
The operator control section, with the exception of
the emergency pull switch, may be duplicated once as
a remote panel on a console.
The following table lists all operator controls by
the names on the panel or controls and describes