IBM System/370 145 Manual page 223

systems for example, use of a 3lJOO-series tape unit offers improved tape
reliability and subsystem servilceability as already discussed.
Conversion of seven- and nin~e-tra.ck NRZI tape volumes can be done
gradually during production processing. That is, the old master input
tape volume is read in on a 3400-series tape unit with the appropriate
compatibility (Dual Density or :seven Track) feature while the new master
output tape is written on a 340t()-series tape unit in 1600-BPI PE format.
Existing programs that process lthese converted tapes need not be
modified unless an altered characteristic (recording mode or block size,
for example) is specified in th4e program DCB. Existing job control for
these programs must
be
altered lto request a tape unit with the new
recording characteristics and, if desired, to change existing DCB
parameters such as block size, number of buffers, etc.
Tapes that cannot be
convert~ed
on an as-used basis, such as program
tapes or active reference tapes that are not rewritten when processed,
can be converted by uSl-ng a cOP){ utility.
CONVERSION TO THE 3505 CARD READER AND 3525 CARD PUNCH
Existing user-written Assembler and high-level language executable
programs for 25lJO, 2501, 2520, Cind 1442 readers and punches can be
executed without change using a 3505 reader or a 3525 punch with
comparable features. Programs 1:hat handle. combined read/punch
operations must be modified. This involves alteration of punch CCW
lists if the EXCP macro i.s stilJL to be used. If the newly defined
access method support of
combinE~d
operations is to be used, EXCP code
must be removed, separate data sets must be defined, and the appropriate
BSAM or QSAM macros must be
addE~d
to replace the EXCP macro. Card data
set DD statements that specifically request allocation of a reader other
than the 3505 (UNIT=2540, for
e)~mple)
or a punch other than the 3525
must be modified.
60:
15 PLANNING OPTIMAL SYSTEM I)ERFORMANCE, USING BLOCK MULTIPLEXER
CHANNELS AND ROTATIONAL
!~OSITION
SENSING DEVICES
Block multiplexing, rotational position sensing, and multiple
requesting p·rovide the user
wi
til another tool that can improve total
system throughput in the area
01:
multiprogramming. However, the
effectiveness of this tool for
ill
given installation depends largely on
proper planning for its use. This section indicates how to use block
multiplexer channels and RPS devices more effectively.
The guidelines outlined indicate how best to configure a system with
rotational position sensing devi.ces, how to plan job scheduling, and
what to consider when determiniIllg disk data set characteristics.
Explanations follow the statemeIlltof each guideline.
All guidelines presented are not necessarily practical for all users.
Each item should be evaluated int terms of the processing requirements
and hardware configuration of aIll installation.
SYSTEM CONFIGURATION AND GENERA'I'ION
Guidelines for system configulration and generation are as follows:
1. Multiple 3330-series stri.ngs should be placed on a single block
multiplexer channel.
Performance improvement occurs (1) as a result of overlapping the
rotational positioning time of disk devices and (2) because more
A Guide to the IBM system/310 Model '145
213