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The contents of auxiliary storage vary depending on the mode, System/370 or
System/370-XA, in effect. During an IML, the required auxiliary storage area is
initialized as appropriate, using information contained on the functional diskette(s).
Auxiliary storage for System/370 mode contains the following in the highest to the
lowest addressed locations:
•
UCW area with a minimum of 128 and a maximum of 2048 UCWs
•
SIOF queuing area
•
I/ 0 trace area
•
Channel error logout area
•
Channel UCW directory area
•
Instruction tracing area
•
Channel data buffer reconfiguration test data
•
Restart text save area
•
Two internal records for the TEST BLOCK instruction (one for unusable
protect keys and one for unusable 4K-byte blocks)
•
Engineering/ scientific assist feature table
•
Program event recording area
•
Control storage link information
•
K-addressable auxiliary storage area of lK bytes. This area contains various
pointers and data fields used by the instruction processing function (pointers to
the beginning of the other areas in auxiliary storage, the time-of-day clock, the
CPU timer, the clock comparator, the interval timer, for example).
For System/370-XA mode, auxiliary storage contains the following in the highest
to the lowest addressed locations:
•
Monitoring data area (32 bytes/subchannel)
•
I/ 0 trace area
•
Channel error log
•
CRW (channel report word) queue
•
Subchannel area
•
Control unit block area (70 bytes/ control unit)
•
Channel directories
•
Channel data buffer reconfiguration test data
38
A Guide to the IBM
4381
Processor
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