Performance Guidelines
Calculate the amount of available real
amount of storage required by CP from
is:
storage (ARS) by subtracting the
the real machine size. Formula 1
r r" I IRM - 256KI I ARS = RM - II + T + 12K + 4KI---------1 I I I 64K II L L .J.J RM is the real machine size.
I is the amount of storage needed to IPL CP. Refer to the load
map produced when the CP nucleus is generated. The amount of
storage needed to IPL CP is all of storage up to, and
including, the module DMKSAV. T is the amount of storage allocated for the CP internal trace
table. CP allocates 4K of storage for each 256K of real
storage for the CP internal trace table:
r , I RM I 4K 1----1 f256KI L .J
If the calculation RM/256K results in a fraction, the result
should be rounded upward to the next higher integer.
12K is the amount of fixed free storage allocated for the first
256K of real storage.
r , IRM - 256KI 4KI---------I I 641{ , L .J
is the amount of fixed free storage allocated for real storage
beyond the first 256K (if there is no virtual=real area). If
the calculation enclosed in brackets results in a negative
value, replace it with zero. If the same calculation results
in a fractional number, disregard the fraction.
The result obtained from Formula 1 is the amount of available real
storage (ARS) for a particular real machine size. This result is needed
to calculate the maximum size of a virtual=real area in Formula 2.
12 IBM VM/37Q Planning and System Generation Guide

Performance Guidelines
Calculate the maximum size of the virtual=real area for a particular
real machine size by recalculating the amount of real storage required
by CP and subtracting that value from the real machine size.. When you calculate the amount of real storage required by CP this time, you do
not permanently allocate free storage for the portion of storage that is
available for the virtual=real area (according to Formula 1). The
result of Formula 2 is the maximum size virtual=real area (VRS) you can
specify for a particular real machine size. Formula 2 is:
r r
, , I IRft - 256K - ARS I I VRS = RM - I I + T + 12K + 4KI---------------1 + 16KI I I 64K I I L L .J .J Use the same value for RM, I, and T as you used in Formula 1. ARS (the
available real storage) is the result calculated from Formula 1. If the
calculation RM - 256K - ARS 64K
results in a negative value, replace it with zero. If the saae calculation results in a fractional number, disregard the fraction (see Examples 1 and 2). 16K is the amount of storage needed at IPL time for
the dynamic paging area. After VM/370 is loaded (via IPL), the size of
the dynamic paging area is the number of pages from DKKCPE to DKKSAV plus 16K.
The following table shows the maximum size virtual=real area you can
specify for some real machine sizes. h 384K
512K
768K HI 2M 104K 232K 484K 732K 1744K Note that in this table it is assumed the value of I is equivalent to
244Kl. lSince the amount of storage required to IPL VM/370 varies with the
inclusion of optional features and the number of devices in DBKRIO, this figure is used in the following example for illustrative purposes
only. Part 1. Planning for System Generation 13