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Table Look Up on Direct Access Devices

IP.com Disclosure Number: IPCOM000080975D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Related People

Kuhne, R: AUTHOR

Abstract

In a disk unit, tables are parts of an addressable record. In order to avoid introducing the whole record into the storage of the CPU, an additional device is set in the control unit to filter the data read from the disk. This device is controlled either by a counter (search for a given table position) or by a comparator (search through a key).

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Table Look Up on Direct Access Devices

In a disk unit, tables are parts of an addressable record. In order to avoid introducing the whole record into the storage of the CPU, an additional device is set in the control unit to filter the data read from the disk. This device is controlled either by a counter (search for a given table position) or by a comparator (search through a key).

Many programs and microcodes use table look-up techniques for fast and efficient operation. The size of the tables varies from hundreds to thousands of bytes. Usually they are brought into the main memory for the "look-up" operation. In small calculators, the transient storage area required for this operation can be an important part of the whole storage.

The subject feature is an additional part of the disk control hardware allowing the saving of memory requirements and execution time. It is controlled by two types of commands issued by the program. These commands are of the "SEARCH" type; however, the search is made within a single record and offers quite different facilities: a) SEARCH the nth position in table T.

The command includes:

- The table identifier ID.

- The length of the members in the table ML.

- The sequence number n of the required member.

b) SEARCH position following key K in table T.

The command includes:

- The table identifier ID.

- The key K.

- The key length KL.

- The length ML of the members in the table (key + argument).

Such a device can use available field-ef...