IBM System/370 Manual page 85

• Those 7074 programs that use unsupported I/O devices or facilities
can be modified to remove the unsupported item and then emulated,
or these programs can be rewritten to run in System/370 mode.
The internal performance (that is, the speed of performing 7074
CPU instructions weighted
by
frequency of use) of the 7074 Emulator
program for the Model 165 is approximately three times that of a 7074
system. The throughput achieved by the integrated 7074 emulator
operating on the Model 165 versus that obtained using an 7074 is
dependent on the characteristics of the 7074 program being emulated,
the hardware resources available to the 7074 emulator, and the number
of other jobs operating concurrently with the emulated 7074 job(s).
Emulator performance is improved when each 7074 channel is emulated
with a single Model 165 channel (2860, 2880, or 2870 selector
subchannel). Total system throughput should be improved by use of
integrated, rather than stand-alone, emulation.
40:15 709/7090/7094/7094II EMULATOR PROGRAM
This emulator is referred to in this subsection as the 7094 Emulator
program. The use of 7094 in the text refers to all 709X systems
emulated unless otherwise indicated.
A Model 165 with the 7094 Compatibility Feature (#7119), 512K (MFT)
or 1024K (MVT) or more of processor storage, and enough I/O devices
for the operating system and emulated 7094 programs is required. An
online printer dedicated to the 7094 emulator is recommended. The
7094 Emulator program requires a minimum partition or region size of
374K in which to execute. This minimum supports two channels with
ten tape units each and one 1560-byte buffer per tape data set. (Note
that buffering, I/O device configuration, performance, etc., will often
necessitate use of an emulator partition or region larger than 374K.)
Table 40.15.1 lists the 7094 system features that are supported
and Table 40.15.2 indicates those that are unsupported. The facilities
supported
by
the Model 165 7094 Emulator program are the same as those
provided by the integrated 7094 Emulator program for the Model 85.
The hardware and I/O devices supported by the Model 165 7094 emulator
are the same as those supported by the Model 65 stand-alone 7094
emulator with two exceptions. The Model 65 stand-alone 7094 emulator
supports 704 emulation and, mixed density tape, but the Model 165 7094
emulator does not. (The Model 85 emulator does not support 704
emulation or mixed density tape either.)
The 7094 Emulator program accepts and produces two data formats
using BSAM:
1. 7094 format tapes written by the Tape Postprocessor program,
a 7094
system~
a 1401 system or 1401 emulator, or the 7094
emulator for the Model 65, 85, or 165. These tapes can contain
embedded tapemarks and mixed mode files, that is, BCD (even
parity) and binary (odd parity) data.
2. Spanned variable-length (OS VBS) format tapes that are produced
by the Tape Preprocessor program or one of the IBM emulators.
Embedded tapemarks and mixed parity data cannot be handled in
this format, but
BCD
(even parity) characters are represented
by using equivalent EBCDIC characters, and a parallel set of
characters is used to represent binary data (odd parity).
Special blocks are created to simulate tapemarks.
VBS format tape volumes can contain OS standard labels in addition
to 7094 labels and can be processed by both OS and emulated 7094
programs. A nine-track 2400-series tape unit or a seven-track tape
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