IBM System/370 Guide

Page of GC20-1730-0
Revised 7/14/70
By TNL GN20-2227
Architecture Implementation Alterations
Two alterations have been made to the system action taken on a Model
165 during the execution of certain instructions common to both
System/310 and System/360 models. The first involves all instructions
that check the validity of operands involved in packed decimal
operations. On the Model 165. an invalid sign in an operand causes
the instruction to be suppressed (never executed) rather than terminated
during execution as is done on System/360 models. Suppression, rather
than termination, of an instruction when an invalid sign occurs insures
that the data fields involved remain unchanged. Therefore, when a
program check occurs, a routine can be executed that inspects the field
that has the invalid sign.
For example, when an invalid sign results from packing an entirely
blank field, the sign can be corrected by programming. and transaction
deletion or program termination is avoided.
The second alteration concerns the recognition of a storage
protection exception during the execution of an EDIT or an EDIT AND
MARK instruction. On a Model 165 a protection exception always occurs
when a pattern character is fetched from a location protected for
storing but remains unchanged during the edit operation. This change
eliminates unpredictable system operation during editing on a Model
165. The occurrence of a protection exception for the situation
described is model-dependent for System/360 models.
Interval Timer (Standard)
The interval timer in decimal location 80 in fixed processor storage
of a Model 165 has a resolution of 3.33 ms instead of the 16.6 ms
resolution (with 60-cycle power) implemented for the standard timer
on the Model 65. Its maximum time period remains 15.5 hours. The
higher resolution of this interval timer will eliminate many of the
problems encountered in accounting routine accuracy caused by task
execution durations that are less than the 16.6 ms resolution.
Time of Day Clock (Standard)
This new clock is a binary counter of 52 bits with a cycle of
approximately 142 years. It is updated every microsecond. Two new
instructions (SET CLOCK and STORE CLOCK) are provided to set the time
and to request that the current time be stored in a specified double-
word of processor storage. The time can be set only when the CPU is
in supervisor state and only when the clock security switch on the
system console panel is in the enable set position.
The time of day clock can be used for more accurate time stamping than
the interval timer. Accurate time of day can be maintained because during
normal operations the clock stops only when CPU power is turned off. The
interval timer cannot be as accurate as the clock for time of day mainte-
nance because it is not updated when the system is in the stopped state,
and its updating may be omitted under certain conditions of excessive sys-
tem activity. The lS.S-hour cycle time of the interval timer is also a re-
striction. The time of day clock better answers the timing needs of tele-
processing and real-time applications.
£PU Cooling
The heat generated by the logic boards in the Model 165 CPU and
its associated power frames is removed by forced air and a closed-loop
water circulation system. Use of a liquid coolant in addition to air
is required because of the amount of heat generated by the densely
packed circuits in the CPU.
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IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English