IBM System/370 Guide

Channel program 2. Initiate the data transfer operation after the seek
is complete.
Command Chaining
Flag
CC
CC
Command
SEARCH 10
EQ
TIC
READ OATA
(10 - sequential
position on the
track)
(Back to search if
10 not equal)
Selector Channel
and Oisk Control
Unit Status
BUSy
(for 12.5 ms
on the average
for a 231q)
(Processor storage BUSy
address of input
area)
When the sector address is known or can be calculated, the channel
program below can be used to retrieve a record from the same BOAM data
set on a 3330 facility attached to a block multiplexer channel. The
records are fixed-length standard format and sector numbers are
calculated from record 10 (by data management).
Channel program 1. Initiate the seek and data transfer operation.
Command Chaining
Flag Command
Block Multiplexer
Channel and Oisk
Control Unit
Status
CC
CC
CC
CC
SEEK
SET SECTOR
SEARCH 10
EQ
TIC
READ OATA
(Seek address)
(Sector number of
sector preceding
desired record)
(10 - sequential
position on track)
(Back to search if
10 is not equal.
With the logic
shown, the first
10 inspected
normally is that of
the desired record
and the TIC command
is not executed.)
Free during
arm motion
Free until
sector found
BUSY
(250 microseconds
average for a 3330)
Busy
(Processor storage BUsy
address of input
area)
The preceding example indicates the advantages of rotational pOSition
sensing used with block multiplexing:
32
• Only one channel program is required to locate a disk record and
transfer the data, thereby eliminating a stand-alone-seek I/O
interrupt and the I/O supervisor processing required to schedule

IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English