Computer Science DepartmentUniversity of Central Florida

Burroughs' B Series Systems

E. A. Hauck B. A. DentPresenter: Yi Ma and Hongliang Gao

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The ObjectivesThe Objectives

• The basic objective in designing the system was to define a complete system, both hardware and software together, to enable programs written in high level languages to be compiled and run efficiently.

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Main Features

• Important features:– Dynamic storage allocation– Reentrant programming– Recursive procedure facilities– A tree structured stack organization– Memory protection– An efficient interrupt system

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ContentsContents

• The Objectives• Main Features• B6500/B7500 Processor• The Stack• Data Addressing• Non-local Addressing• Multiple Stacks and Re-Entrant Code• The Operating System• Summary

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B6500/B7500 Processor

• Basic machine instruction: operator syllable– 8 bits to a maximum of 96 bits

• Hardware implemented stack• Data word

– 51 bits (3 bits tag + 48 bits data)– Tag: data/operator, memory protection

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The StackThe Stack

Stack memory area

WORD ntx

Stack area assigned to

program

WORDn

TOS WORD

Stack area currently in

use

Stack limit register

SL (Stack Limit)

BOS (Base of Stack)

A

B

X

Y S

Top of stack registerIN/OUTPUT Path of data

to stack

Fast. Can hold two operands.

If double precision, A+X & B+Y.

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Data AddressingData Addressing

• Three mechanisms:– Data Descriptor (DD)/ Segment Descriptor (SD),

• Addresses which are located outside of the job's stack area.

• Absolute machine address.– Indirect Reference Word (IRW),

• Relative address• Address within the immediate environment of the

job's stack– Stuffed Indirect Reference Word (IRWS).

• Relative address• Beyond the immediate environment of the

current procedure

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Non-Local AddressingNon-Local Addressing

• Facility for storing the dynamic history of a program under execution– Stack history list – Addressing environment list

• Mark Stack Control Words (MSCW)

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Non-Local Addressing

MSCW DF

Outer program block

MSCW DF

Procedure ‘C’

MSCW DF

Procedure ‘D’

MSCW DF

Procedure ‘A’

TOS WORD

MSCW DF

Procedure ‘B’

S

F Stack history list

The program{A{

B{} B;

}C{ real v4; D{

A; } D;

} C;}

• Procedures are entering …

• Procedure B exits.• Non-Local Addressing Problem

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Non-Local Addressing cont.

• Address Couple:– The

lexicographical level

– The index

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Non-Local Addressing cont.

MSCW

TOS WORD

MSCW

MSCW

MSCW

MSCW

DISP DF

DISP DF

DISP DF

DISP DF

DISP DF

Outer program block

Procedure ‘C’

Procedure ‘D’

Procedure ‘A’

Procedure ‘B’

S

FStack history list

D0

D1

D2

D3

D4

D31

Display registers

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Multiple Stacks and Re-Entrant CodeMultiple Stacks and Re-Entrant Code

• Code sharing

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The Operating SystemThe Operating System

• The operation of the system was to be directed by a Master Control Program (MCP)

• Supports multiprogramming• 40 interrupt conditions (including timing interrupt)

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SummarySummary

• Hardware:– Multiple Stacks

• Programming:– Be done in ALGOL and COBOL

• Main features:– Dynamic storage allocation– Reentrant programming– Recursive procedure facilities– A tree structured stack organization– Memory protection– An efficient interrupt system

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ReferencesReferences

1. “Burroughs’ B6500/B7500 Stack Mechanism”, E. A. Hauck and B. A. Dent, Chapter 16 of Computer Structures: Principles and Examples, McGraw-Hill, 1982

2. “Operating System For The B 5000”, C. Oliphint, 1964

3. “Studies In Operating Systems”, R. M. McKeag and R. Wilson, Academic Press, 1976

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Thank you!

Questions?