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
Performance Guidelines
Determine the maximum size of the virtual=real area for a real machine
with 768K of storage that executes a VM/370 system that requires 244K to 1PL. r r, r " I 1768K I 1768K - 256KII ARS = 768K - 1244K + 4KI----1 + 12K + 4KI-----------1 I I 256K I I 64K i I L L.J L .J.J ARS = 768K -[244K + 12K + 12K + 32K] ARS = 768K - 300K ARS = 468K r r , I 1768K - 256K - 468KI VRS = 768K - 1244K + 12K + 12K + 4KI------------------I I I L L
r r, , I 144K, I VRS = 768K - 1268K + 4KI---1 + 16K I I 164K I I L L .J VRS = 768K -[268K + 4K[O] + 16K] VRS = 484K
.J
Note that the fraction (44/64) resulting from the RM - 256K - ARS 64K
calculation in Formula 2 is truncated to zero.
64K
14 IBM VM/370 Planning and System Generation Guide , .J
, I + 16K I I .J
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