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Chapter 2. Organization
Contents
2-1
2-2
2-2
2-2
2-3
2-3
2-3
2-4
2-4
2-4
Logically, IBM 4300 Processors consist of main
storage, a central processing unit (CPU), operator
facilities, and channels. The channels allow
input
I
output
(II
0)
devices to be attached, usually
through control units. (See the figure "Logical
Structure. ")
Specific processors may differ in their internal
characteristics, the number and types of channels,
the size of main storage, and the representation of
the operator facilities. The differences in internal
characteristics are apparent to the observer only as
differences in machine performance.
Main
I
CPU
Storage
I
I
I
Channel
Channel
/
I I
1 1
I
o
0
1/0
Devices
o
0
Logical Structure
Main Storage
The 4300 Processors provide fast-access main
storage and storage-control functions for high-
speed processing of data by the CPU and channels.
The storage-control functions permit main storage
to be controlled at two levels: real storage and
virtual storage.
Real storage is the storage where data and
instructions actually reside at the time they are
accessed by the CPU and channels, but neither
CPU programs nor channel programs can address
real storage directly. The size of real storage
depends on the model.
Virtual storage allows both CPU programs and
channel programs to address an apparent main
storage of up to 16,777,216 (16M) bytes. Virtual
storage may be larger than the underlying real
storage.
If
the virtual storage is larger than the real
storage, a supervisory control program using the
storage-control fU11-ctions of the machine is required
for controlling which parts of virtual storage are
currently mapped onto real storage. This control is
dynamic and transparent to the other programs
except for the time delay.
Chapter 2. Organization
2-1
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