IBM System/370 145 Manual page 227

as possible. When BSAM is used, the programmer must handle the
initiation of I/O requests.
The following summarizes the advantages of rotational position
sensing, multiple requesting, and block multiplexing.
• System throughput increases can be achieved when multiple sequential
data sets are processed concurrently on a single block multiplexer
channel (using QSAM, QISAM, or BSAM) because a higher effective
channel data rate results.
• The number of block multiplexer channels required in a given system
configuration can be fewer than the number of selector channels that
would
be
required to handle the same amount of data, because more
effectble channel utilization is achieved by block multiplexing disk
operations.
• The performance cost to' an installation of verifying disk write
operatiO'ns is sharply reduc1ed.
• The greatest throughput impJ['ovement results from use of rotational
pO'sition sensing with high-,activity, transaction-based processing,
that is., with applicatiO'ns ·that include O'ne or more large jobs that:
1. Use direct processing
(Bl()AM)
with fixed-length standard or VBS
records and a record reflerence that includes ID
2. Require a multiple volumle data base of small records
3. Process many additiO'ns and updates and use write verify
60:20 OS MFT AND MVT PORTABILrry
To avoid multiple system gen4erations, an OS MFT or MVT tiser with
multiple Model 145 systems may 1~ish to generate a single operating
system that can be used on eve~~ Model 145 in the installation. This is
possible under the same system hardware and I/O device configuration
restraints that exist for Systelll/360 models. During the IPL procedure,
channels and I/O devices may have to be varied offline, partition sizes
may have to be redefined, etc., when. the operating system is used with a
different configuration than Wal:l specified durin~ system generation ..
A user with both a system/310 Model 145 and a System/310 Model 135 or
155 or a system/360 model in an installation may also wish to generate
one operating system that can be used on both models. This approach
provides backup when one system is unavailable and can eliminate the
necessity of multiple generatiO]ls.
The system generation procedure is modified to' allow generation of an
operating system that is portable among System/370 Models 135 and up in
BC mode. Specifically, the SEClltfOD.S system generation macro will be
changed to cause the inclusiO'n of all the required model-dependent
rO'utines (such as MCH, EREP,
et4~.)
for both the primary CPU and each
secondary CPU indicated by the user. When a System/310 model is the
primary model, MCH can
be
speciJEied in the SECMODS macro as the error
recovery routine for each seconciary model. At IPL, the appropriate
model-dependent routines are initialized, based on the CPU
identification.
Previously, only an SER routine could be specified for secondary
CPU's and this support
continue~J
for System/360 models. Hence, an OS
operating system can be
generat4~d
to include multiple MeH routines for
System/310 CPU's or multiple SEll routines for System/360 CPU's: however,
A Guide to the IBM System/310 Model 145 211