IBM 2790, Manual

Page: 54 / 88

(1
= restored).
r? = Blank (X‘40’)
rg ,r^ = Status of segment A:
X‘F4F0’-Segment restored and OK.
X‘F0F1’-Segment was already bypassed,
or was requested to be bypassed.
X‘F0F2’-Segment had to be bypassed
because nothing was received from
segment.
X‘F0F3’-Segment had to be bypassed
because it could not successfully pass
500 frames error free.
X‘FnFm’ (where X‘nm’ form an area
station address)—Segment had to be
bypassed because of a break, and the
address of the first area station down­
stream of the break is X‘n m \
XTOFO’-Segment bypassed due to 2790
adapter failure.
r 10’ r l 1 = $tatus of segment B (see rg, rg above).
r
1 2
> r i
3
= Status of segment C (see rg, r^ above).
r 1 4 ,r 15 = Status of segment D (see rg, rg above).
r 16 = New line.
r
17
—r
11
6 = (As required.) EBCDIC format of the
binary address of area stations bypassed
in executing this request (two bytes per
address).
r l 17 = If more than 50 area stations were by­
passed, new line character is inserted
i n r 128~r 137-
r 118~r217 = (Same as r i
7
—r
115
above.) As required.
Restart-Number Logging
A restart number is included in the message header of every
message sent to the CPU. These numbers are intended to
allow data recovery when either the 2790 system hard stops
or the user program has checkpoint/restart capability.
Priority-message restart numbers have the hexadecimal
formats “XX2X” and “0020” (the latter is called a “zero
restart number”). Zero restart numbers should not be
logged; the other format should. Priority-data restart num­
bers need not be checkpointed, if this facility is available,
since priority data is not recoverable in a checkpoint/restart
operation. When the disk is successfully re-initialized, the
re start-number log should be set to zero.
All deferred-message restart numbers have the hexa­
decimal format “XX4X” , and all should be logged. If
checkpoint/restart capability exists, the deferred-restart
number log should be checkpointed. After successful disk
re-initialization, the deferred restart-number log should also
be set to zero.
Logging is defined here as saving the last restart number
received, not storing every number as it is received. Both
priority and deferred re start-number logs should be set to
zero when the 2715 is ICPL’ed.
Core Storage
The basic 2715 uses a 16K-byte ferrite core storage unit for
storing control programs and for message buffering. The
core storage unit has a word width of 18 bits and a cycle
time of 1.2 microseconds. The basic 16K-byte core storage
provides up to 1280 bytes for transaction tables; the
Expanded Capability feature increases the transaction-table
storage to 4096 bytes.
System/360 Reset
System/360 reset will terminate all 2715 Model 1 multi­
plexer channel adapter operations. All other operations
will continue normally.
2715 P E R F O R M A N C E
The performance of the 2715 can be specified from several
points of view. It is discussed here in terms of sorting
speeds, and in terms of channel throughput.
Sorting
Sorting speed is a function of a number of factors. The
most important of these are:
1. Input rate in characters per second.
2. Time it takes an operator to enter the transaction.
3. Frequency and duration of traffic peaks.
4. Percentage of message-routing transactions.
The sorting algorithm has a speed of 150 to 200 charac­
ters per second. If the entry rate is below this value, the
algorithm will sort as fast as
transactions are completed.
When the entry rate exceeds this value, the sort file begins
to build up and sorting proceeds more slowly. When there
are long delays between entries of a transaction, as with an
inexperienced operator, the sort will also proceed more
slowly, as this causes the sort file to become larger and
more data entries must be examined to assemble the tran­
saction. These delays are only temporary, however, since
the sort can catch up rapidly when this peak traffic subsides.
The operator at the area station is not aware that sorting
is being delayed. Another factor that affects the sorting
speed is the volume of message-routing transactions, especi­
ally those with implicit text. This effect would be significant
only in a system with very large volumes of message routing.
Channel Throughput
In discussing channel throughput, consider three modes of
operating the system with respect to the System/360
processor.
On-Line. In this mode, the multiplexer channel is available
at all times and, except for deferred data, little data buffer­
ing is required in the 2715. With the Model 1, the multi­
plexer channel adapter has a maximum data-transfer rate of
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