IBM System/370 Guide

40:10 7070/7074 EMULATOR PROGRAM
The OS 7070/7074 Emulator program for the Model 165 (hereafter
referred to as the 7074 Emulator program) requires a Model 165 with
the 7074 Compatibility Feature (#7117), 512K or more of processor
storage~ and enough I/O devices for the operating system and emulated
devices. The emulator program requires a minimum processing partition
or region of 188K in which to operate. This minimum supports a 7074
configuration of 10K words, two channels, seven tape drives per channel,
and single buffering with 2000-byte buffers for each tape data set.
(Note that buffering" I/O device configuration, performance, etc.,
will often necessitate use of an emulator partition or region larger
than 188K.)
Table 40.10.1 lists 7074 system features that are supported and
Table 40.10.2 indicates those that are unsupported. (see Emulating
the 7070/7074 on the IBM System/370 Model 165 Using OS/360, GC27-6948,
for an indication of how unsupported instructions are handled by the
emulator.) The 1074 emulator also can emulate 7070 programs that do
not contain elements that are incompatible with the 1074, as discussed
in IBM 7070/7074 Principles of Operation (GA22-7003). The Model 165
7074 emulator supports the same facilities as the Model 65 stand-alone
7074 emulator except that 7074 unit record devices (7500 Card Reader,
7550 Card Punch, and 7400 Printer) are supported by the Model 65
emulator but not by the Model 165 emulator.
The 7074 Emulator program accepts and produces two tape data formats
using BSAM:
1. 7074 format tapes, written in BCD, that are written by a 7074
system, a 1401 system (or a 1401 emulator), the stand-alone
7074 emulator, the Model 165 integrated emulator, or the Tape
Postprocessor program. These tapes can contain segment marks
and embedded tapemarks but cannot contain binary (odd parity)
format data. Mixed density, seven-track input tapes can be
handled if single buffering is used and the tape density
specified in the DD statement is that of the first record on
the tape.
The user is responsible for end-of-volume switching for
multivolume 7074 format tape files. Tapes in 7074 format can
be processed on nine-track and seven-track 2400 tape drives.
The latter must be attached to a control unit with the Seven-
Track compatibility Feature. Tapes in 7074 format must also
be designated as unlabeled as far as OS is concerned and their
record format must be specified as undefined.
2. Spanned variable-length (OS VBS) format tapes, written in EBCDIC,
that are produced by the IBM Tape Preprocessor program or as
a result of 7014 emulation on a Model 165. These tapes can
be read by both System/370 and emulated 7074 programs. End-
of-volume switching is handled by as data management and is
therefore transparent to the 7074 programmer. (Thus, if a 7074
program depends on an end-of-volume indication, 7074 format
should be used.)
VBS format tape volumes can be processed on a nine-track 2400 tape
unit or a 2400 tape unit with a seven-track head and the Data Converter
feature. These volumes can have unlabeled data sets or standard OS
labels in additon to 7074 labels. Note that VBS format files also
can be processed on direct access devices.
60

IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English