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Standardized System Control Blocks

IP.com Disclosure Number: IPCOM000076776D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Stevenson, DA: AUTHOR

Abstract

A means is provided for standardizing the definition and accessing method of system control blocks in order to facilitate their static and dynamic creation, compression, or extension. It is based on a standard S/360 word of 32 bits as the smallest separately assignable field. Only those fields necessary for the particular occurrence of the control block exist during its lifetime.

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Standardized System Control Blocks

A means is provided for standardizing the definition and accessing method of system control blocks in order to facilitate their static and dynamic creation, compression, or extension. It is based on a standard S/360 word of 32 bits as the smallest separately assignable field. Only those fields necessary for the particular occurrence of the control block exist during its lifetime.

The Standardized System Control Block (SSCB) format is shown in the Figure and is defined as follows: o One word which always exists, SSCB descriptor word 1

o Zero through 30 words

o One word, optional, SSCB descriptor word 2

o Zero through 30 words

o Repeat of SSCB descriptor word, zero through 30 word groups.

Each word in the SSCB, except SSCB descriptor word 1, has a corresponding bit position in a SSCB descriptor word. If that bit position is one, the corresponding word exists in the control block. If the bit is zero, the word is either not defined or not applicable to this occurrence of the control block. The presence of additional SSCB descriptor words, after the first, is controlled by the last bit in the previous SSCB descriptor word. A control block is thus open-ended for future definition and use.

Any given field in an SSCB is accessed by testing its defined bit position in a SSCB descriptor word. If "0", the field does not exist. If "1", count all 1 bits to the left, multiply by 4, and add address of SSCB descriptor word. The result is address of desired field. Location of SSCB descriptor words (after the first) are done similarly.

In order to reduce programming overhead when accessing control blocks, at least one new hardware instruction is necessary as follows: Load Address, Control Block Field LACBF R1, R3, D2(B2) (RS).

(Image Omitted)

R3 points to the first word of the control block (SSCB descriptor word 1) containing the single-word field to be accessed. The effective address developed from B2, D2 is used as an unsigned number to uniquely identify the desired field. If the desired field is present, its address is returned in R1; othe...