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Variable Skip Factor Algorithm

IP.com Disclosure Number: IPCOM000086907D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Durst, DD: AUTHOR [+2]

Abstract

The use of a skip factor is known for the purpose of synchronizing a cyclical memory with a program to minimize waiting time by either the memory, which might cause overruns, or by the program, both of which affect throughput. For example, logically sequential 256 byte blocks of data may actually be spaced apart by five blocks in a record on a disk if the skip factor is five.

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Variable Skip Factor Algorithm

The use of a skip factor is known for the purpose of synchronizing a cyclical memory with a program to minimize waiting time by either the memory, which might cause overruns, or by the program, both of which affect throughput. For example, logically sequential 256 byte blocks of data may actually be spaced apart by five blocks in a record on a disk if the skip factor is five.

The problem with known skip factors is that they are not variable and therefore cannot be optimum for many programs. If one or more skip factors are written onto a standardized disk location, e.g., track 0, the disk I/O support program can utilize the optimum skip factor in the algorithm shown below. Alternately, an optimum skip factor could be loaded from a terminal with the program at system initialization to avoid the need for a standardized skip factor location on disk.

The general algorithm is:

1. N = L.A. x S.F.

2. If N > L.R. - 1

3. N = N + 1 - L.R. and go to 2

4. Else P.A. = N where:

L.A. = Logical Address received from a data base

management program;

P.A. = Physical Block Address on the disk;

L.R. = The largest number of blocks in a record

on the disk; and

S.F. = The block skip factor number received from

the standardized disk location or from a

terminal during system initialization.

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