jbeard@quintus.UUCP (Jeff Beard) (10/04/89)
To avoid i/o wait time and to max(transaction rates), the ACP (Airlines Control Program) of prior years used interesting file layouts. Of a disk farm of N disks, (assuming M tracks/cylinder each) the sequence of sequential records R1,R2,...Rn were distributed to cylinder 0, track 1, record 1, (disk1, disk2, ... diskN). The Nth+1 record started at cylinder 0, track 2, record 1 and the 2N+1 was at cylinder 0, track 3, record 1 and so on. Thus after initaily seeking N arms (asynchronously), N*M records could be transferred without arm movement. By the wonders of S/360 channnel programming, the new arm positioning for the next round was restarted when the last record from disk 1 track M was transferred, while disk 2 track M data transfer was in progress. Thus continuous, asynchronous data transfer required only rotational+transfer time.