IBM System/370 145 Manual page 12

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• The following are CPU features of the Model 145.
Implementation of a basic control mode and an extended control mode
of system operation is standard. When the Model 145 is operating in
BC mode, DOS Ver'sions 3 and 4, OS MFT, and OS MVT can be used. When
the Model 145 operates in EC mode, the PSW format and the layout of
permanently assigned lower processor storage are altered to support
additional system control and new functions (such as dynamic address
translation) that are not provided in BC mode. DOS/VS, OS/VS1,
OS/VS2, and VM/370 support EC mode operations. with a few
exceptions, existing user-written problenl programs that operate
under DOS Version 4, OS MFT, or OS MVT can operate under DOS/VS,
OS/VS1, or OS/VS2, respectively, without modification.
Dynamic address translation (DAT) is a standard facility that can
operate only in EC mode. It provides translation of addresses
during program execution. One virtual storage of up to 16 million
bytes or multiple virtual storages of up to 16 million bytes each
can be supported using DAT hardware. (The size of the virtual
storage that can be efficiently supported on a Model 145 depends on
the hardware configuration and job stream characteristics.) DAT is
a standard feature on all System/370 models that have EC mode. In
System/360, DAT is implemented only in the Model 67.
Channel indirect data addressing is also standard and is provided to
handle I/O operations when DAT is used, because an I/O buffer area
can span a set of noncontiguous processor storage areas.
The Model 145 standard instruction set includes new general purpose
instructions in addition to the powerful System/360 instruction set.
These instructions enhance decimal arithmetic performance, simplify
the handling of nonword-size data that is processed using the
general registers, eliminate the need for multiple move or compare
instructions or move subroutines, simplify system mask handling, and
facilitate record blocking and deblocking, field padding, and
storage clearing. Other new instructions are provided primarily for
control program use.
A floating-point arithmetic option is available that provides for
floating-point operations, including extended precision operations.
Precision of up to 28 hexadecimal digits, equal to up to 34 decimal
digits, is provided by the extended precision data format.
A monitoring feature is standard that can be used to trace user-
defined program events for the purpose of debugging or statistics
gathering.
Program event recording is standard and also is designed to be used
as a problem determination aid. This feature includes hardware that
monitors the following during instruction execution: successful
branches. the alteration of general .registers, and instruction
fetching from and alterations of specified areas of processor
storage. It can operate only when the Model 145 is in EC mode .•
An interval timer of 3.33-ms resolution to improve job accounting
accuracy is standard. (A 16.6-ms resolution timer is provided for
Models 30 and 40.)
A time of day clock is included as a standard feature to provide
more accurate time of day values than does the interval timer. The
clock has a 1-microsecond resolution.
The CPU timer and the clock comparator are optional. The CPU timer
provides an interval timing capability similar to that of the
interval timer at location 80 but it is updated every microsecond,
A Guide to the IBM System/370 Model 145