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Reprintedfrom:
Proceedings of
Fourth Australian
Computer Conference
By J. C. CLEARY
Adelaide~ South Australia
August 11-15th~ 1969
Proceedings of Fourth Australian Computer Conference
Adelaide, South Australia, 1969
By J. G. Cleary
BurroughsCorporation,Pasadena,
California,U.S.A.
ABSTRACT: The approach to process handling embodied in B6500 hardware and software
design and implementation is discussed in this paper. Hardware features necessary to the
understanding of the approach are first described. Some aspects of the language ESPOL-an
extended ALGOL language used for writing the B6500 Executive System-are presented. The
representation of active and inactive processes by active and inactive stacks is discussed.
Implementation of process interlocking facilities is described. Some aspects of B6500 core
protection are discussed. There follows a description of the usage and implementation of events
and the concept of "software interrupt" is introduced and discussed. Finally, it is claimed that
the paper demonstrates how the basic B6500 desigu philosophy has assisted in the implemen-
tation of process handling. The emphasis throughout the paper is on description of a working
system, rather than theoretical discussion.
KEY WORDS AND PHRASES: Process, processor, multiprogramming, multiprocessing,
dynamic relocation, dependentprocess,
active process,Algol, event,state vector, tree, locking,
queue.
COMPUTING REVIEWS CATEGORIES: 4.20, 4.21, 4.22, 4.31, 4.32, 6.20, 6.21.
INTRODUCTION DATA WORDS
The B6500 is designed for the multiprogramming/multi- 1 0001
000 ! EXPONENT!
EXPONENT MANTISSA
MANTISSA !SINGLE
PRECISION
processing en,ironment where the process, rather than the job OPERAND
or program, is considered as the basic processing unit. I I I DOUBLE
This paper describes how the B6500 system controls the
0
EXPONENT
MANTISSA
(MS)
PRECISION
running of independent and dependent processes. An intuitive OPERAND-
I
010
11
I
i
EXPONENT
i
MANTISSA
(MS)
understanding of the meaning of the term "process" is assumed I I ,1ST. WORD
(but see Dahm, Gerbstadt and Pacelli, 1967; Dennis and Van I 010 IE~PONENT(MS) i MANTISSA (LS) i DOUBLE
010 EXPONENT(MS) MANTISSA (LS) PRECISION
Horn, 1966; Lampson, 1968). OPERAND
I- I I 2 ND. WORD
6BITS ~1~39BITS -I
SYSTEM ORGANISAnON DESCRIPTORWORDS
The division of the B6500 system into hardware and software I ono I n I I 0 ~'O"TU I .nnD~"" I DATA
components was dictated by economic rather than technical 1101 I ~ I ! LENGTH! ADDRESS! DESCRIPTOR(DD)
considerations. Thus, the distinction between hardware and
software functions is considered relatively unimportant, and I I I
I no 0 I D Ii, ~'o,,"u i 'nnD~~~ i SEGMENT
will be noted only in this section. I 011 I PI! LENGTH! ADDRESS! DESCRIPTOR(SD)
The B6500 has been discussed elsewhere (Hauck and Dent,
1968; Hillegas, 1968) and only those details considered neces- 1.-20BITS ~I. 20BITS-1
sary to the understanding of the current subject are discussed SPECIAL CONTROL WORDS
here. I 011 I ! ~TACK NO. ! DISPLACEMENT! ! DF I MARK STACK
011 STACK NO. DISPLACEMENT DF CONTROL
WORD (MSCW)
Hardware/Software Integration I I I I
The B6500 hardware has been designed to operate under the PROGRAM ADDRESS PROGRAM
control of an executive program (MCP or Master Control SYLLABLE INDEX COUPLE WORD(PCW)
CONTROL
Program), and to be programmed only in higher level lan-
guages (e.g. ALGOL, COBOL and FORTRAN)-there is no I
PROGRAM ADDRESS RETURN
assembler. Thus, machine design must facilitate the implemen- 011 SYLLABLE INDEX COUPLE CONTROL
tation of fast compilers producing efficient machine code. WORD (RCW)
The command structure of the B6500 is Polish string and the I I I I
instructions manipulate the contents of a stack. The stack not 1 001
001 Ii: : ! ADDRESS
AcDt.f~Cf I REFERENCE
INDIRECT
only facilitates the execution of Polish code, but also provides COUPLE WORD (IRW)
an efficient means of handling recursion. I I I I STUFFED
Efficient compiling techniques typically produce a Polish
string, usually as the first of two or more steps in the transla- I 001
OOlt i STACK No.1
NO. DISPLACEMENT!
DISPLACEMENT ! DELTA IINDIRECT
REFERENCE
tion of source code to machine language; they also seem I , I I WORD (IRWS)
naturally biased towards the use of recursive procedures (Ran- 1 011 I i sTrfES!
!F !: DS:! OF TOP OF STACK
dall and Russel, 1964). Hence, one-pass compilation of 011 STATES DS OF CONTROL
WORD (TOSCW)
efficient code is possible.
Instructions and Word Formats