IBM Series 1 User Manual page 233

TNL: GN34-0368 to GA34-0033-0 (February 4,1977)
.!lni! 1Q~Q ~uivalences. Unit load substitutions may be made
on the
110
channel using the following equivalence
definitions dnd rules.
The I/O channel feature sockets in the processor and I/O
expansion card files represent an available resource in the
system. A unit of available sockets (UAS) is a subset of
this total resource for planning and application purposes. A
UAS is defined as the physical group of sockets available:
1. Outboard of the processor to, but not including, the
first channel repower feature.
2.
Outboard of any channel repower feature, but not
including the next channel repower feature.
3.
Outboard of the last channel repower feature installed
on the system.
In a given UAS for case 1 above the total connected load for
a 4955 is:
[(NO. of general loads) +2 (No. TTL unit loads)] 520.
(No. of TTL unit loads) 58
Because the channel repower feature represents one general
unit load, the maximum stated above is increased to 21 if
the configuration does not contain a channel repower
feature. The 4953 Processor is limited by the physical size
of the card file, not the drive capability of the channel.
For cases 2 and 3:
[(NO. of general loads) +2 (No. of TTL units)]
~14
(No. of TTL unit loads) 58
A UAS may not contain more than one cable and the cable must
be less than 1.6 metres long.
A special case of a unit load substitution is for an
attachment that presents a TTL unit load in all respects,
except that any of its type A-A, A-B, or
A-C
receivers
always presents an active receiver load (-1.6
rnA
at 0.4V).
This type of load is called a TTL selected load. A maximum
of one TTL selected load attachment can be substituted for
one general unit load attachment in
any
unit of available
drops. No TTL unit loads
may
coexist in a unit of available
drops containing a TTL selected load.
2-72
GA34-0033