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Given the following, the storage key
of block D will be set to 1 •
.-~-r-l
Instruction
lOt 813151
(hex)
L-..L-..L-..L-
J
r-T-T-T-r-T-T-T-l
Register 3
I
0
I
0
I
0
I
0
I 0 I
4
111
0
I
(hex)
L_~_~~~~_~_~_J
r-~T-~T-T-T-r-1
Register 5
I
0
I
0
I
0
I
0
I
0
11 I
41 0
I
(hex)
L_~~~~_~_~_~_J
Storage Block
Rey
A
6144-8191
0
B
C
D
4096-6143
2048-4095
0000-2047
o
o
1
General register 5 contains the hexa-
decimal address
140.
This means that
bit-positions
8-20
of register 5 are
1-72
zero.
Thus block D, the first block of
2048,
has its storage key set to 1.
USING STORAGE PROTECTION
The set storage key instruction is a
privileged operation.
It may be issued
only when bit
15
of the PSW (problem
state bit) is zero.
In a typical
supervisor-controlled operation, the
supervisor causes a problem program to
be read into main storage.
The
supervisor sets the storage keys for the
area of storage used by the problem
program.
The supervisor assembles the
PSW to
be
used by the problem program.
This assembled PSW has a protection key
that matches the storage keys associated
with the problem program.
Once the
function of loading a problem program
into main storage and assigning the keys
for storage protection is done, the
supervisor passes control to the problem
program with the Load PSW instruction
whioh specifies the assembled PSW
(Figure 1-31).
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