IBM 4381 Manual page 15

The Mathematical Function Facility (not implemented in 4341 Processors) is
standard in 4381 Model Group 12, 13, and 14 Processors and provides a group
of eight register-to-register floating-point instructions that perform elementary
mathematical functions. The supported functions are exponentiation and
natural and common logarithms. The instructions support short and long
precision for the two operands involved (see Section 20:05). This facility
reduces processor busy time by up to 65 percent for the assisted functions. It
permits selected scientific subroutines to be executed faster than with
conventional programming (FORTRAN subroutines).
Timing and debugging features like those in System/370, 30XX, and other
4300 Processors (3.3-ms-resolution interval timer, time-of-day clock, CPU
timer, clock comparator, monitoring feature, and program event recording) are
standard in 4381 Processors. The time-of-day clock and CPU timer have a
one-microsecond resolution.
The standard byte-oriented operands facility permits byte boundary alignment
for the operands of nonprivileged instructions, making it unnecessary to add
padding bytes within records or to blocked records to align fixed- or
floating-point data. In 4381 Processors, minimal performance degradation
results from the use of unaligned data.
Functions of the System/370 Extended Facility/Feature for 30XX Processors
are standard in 4381 Processors. These facilities are low address protection (to
protect the contents of locations 0 to 511 from accidental modification), the
TEST PROTECTION and INVALIDATE PAGE TABLE ENTRY
instructions (for control program use), the common segment facility (to
improve address translation performance for MYS and VM/370
environments), MYS-dependent instructions (ECPS:MVS feature in 4381
Processors), and Virtual Machine Extended Facility Assist.
The facilities provided by the 3033 Extension feature for 30XX Processors are
standard in 4381 Processors. The Dual Address Space Facility for both modes
(which improves the performance of MYS/SP Cross Memory Services),
START 1/0 FAST RELEASE instruction queuing for System/370 mode only
(which is basic to the System/370-XA mode channel subsystem), and two
MYS assists (included in the 4381 ECPS:MVS feature) are implemented in
4381 Processors. The suspend and resume facility provided by the 3033
Extension feature is not implemented for 4381 System/370 mode of operation
but a comparable function is basic to the channel subsystem defined for
System/370-XA mode.
Dynamic address translation and channel indirect data addressing features to
support a virtual storage and/ or virtual machine environment are standard.
For System/370 mode (which uses 24-bit addressing), one virtual storage of
16,777,216 bytes (16Mb) maximum or multiple virtual storages up to
16M-bytes each can be supported. For System/370-XA mode (which uses
31-bit addressing), one virtual storage of up to 2,147,483,648 bytes (2
gigabytes) or multiple virtual storages of up to 2 gigabytes each can be
supported.
A segment protection facility (not provided for 4341 Processors) that provides
the ability to prevent stores to protected virtual storage segments is standard
for System/370 mode. For System/370-XA mode, a page protection facility is
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A Guide to the IBM 4381 Processor