IBM System/370 Manual page 76

Page of GC20-1 7 30-0
Revised 7/14/70
By TNL GN20-2227
generates them for processing programs that use extended precision data.
A program check interrupt occurs if an extended precision instruction is
executed and the feature is not present in the system. This interrupt
causes the processing program to call in a subroutine to handle extended
precision operations. Extended precision divide is always simulated,
because the extended precision facility does not include such an
instruction.
Interval timer. The interval timer will be supported for the same
functions as it is currently except for time of day values.
Time of day clock. This clock will be supported in MFT and MVT
environments for time of day requests made by system and user tasks
via the TIME macro. At IPL, the operator will have the option of
validating the clock time and correcting an invalid value.
Byte boundary alignment. The programmer can byte-align binary
and floating-point data in Assembler Language programs, in ANS
COBOL programs (by omitting the SYNCHRONIZED clause), in PL/I
programs (by specifying the UNALIGNED attribute), and in FORTRAN
programs. However, OS still expects the parameters passed to it to
be properly aligned and the high level language translators still
align unaligned binary and floating-point data prior to its use.
7080, 7070/7074, 709/7090/7094/709411 Compatibility Features. Three
separate, mutually exclusive emulator programs will
be
provided.
Emulator programs are discussed in Section 40.
Channels. One or two 2870 Multiplexer Channels and up to twelve
high-speed channels (2860 and 2880) in a system will
be
supported.
Both selector and block multiplexer mode of operation will be
supported for 2880 channels. During IPL, block multiplexer mode is
established via a control register bit setting (discussed in Section
10:20) if the user requested block multiplexer mode for at least one
2880 channel at system generation. The operator does not have the
option of changing this mode at IPL, nor does the control program alter
the mode during system operation.
The 3330 facility. The 3330 facility will be supported as an I/O
device for most of the same functions as is the 2314 facility and by
ASP and HASP. The error recovery routine provided for the 3330 will
include support'of the new hardware error correction features.
54
RPS will be supported in MFT and MVT environments as follows •
• The stand-alone seek issued within the I/O supervisor (lOS) will
be eliminated for RPS devices (3330 facilities). lOS will continue
to issue stand-alone seeks for direct access devices without RPS.
lOS will also be capable of recognizing the channel available
interrupt •
• Access method support of RPS commands (SET SECTOR and READ SECTOR)
will be provided tiy:
QSAM and BSAM for all record formats and functions except the
undefined track overflow record format
ISAM for all Updating and verification and for QISAM sequential
processing
BPAM for processing directory and member processing
operations where possible
BDAM for direct retrieval and update of fixed-length standard and
VBS format records without key and for write verification of
all BDAM format records