Unisys History: EXEC II
Randy Carpenter
Unisys History
Volume 1, Number 3
March 1993
EXEC II
by George Gray
The operating system used today on the 1100 and 2200 Series is an
outgrowth of EXEC 8 which was written for the UNIVAC 1108 in the late
1960s, but EXEC 8 was not the first UNIVAC operating system. Its roots go
back to EXEC I and EXEC II, which is why in its early years EXEC 8 was
often written as EXEC VIII. I found a copy of the EXEC II Programmers
Reference for the 1106/1108 (UP-4058 Rev.1), which makes it possible to
take a closer look at the early UNIVAC operating systems.
In the beginning, computers did not have operating systems. The
computer operator set up the computer to run each program. This involved
loading the program into memory from magnetic tape, paper tape, or punched
cards, and then mounting tapes or loading cards for data input/output.
The program itself had to perform all the input/output handling: if it
expected the output tape to be on drive 2, then an output tape had better
be there. To some degree, this inflexibility could be overcome by
switches or jumper cables, but the whole process was very cumbersome, and
wasted time between programs.
The early large-scale computers, such as the UNIVAC I and 1103 and the
IBM 701 and 704 were very expensive, selling for one or two million
dollars, back in the mid-1950s, when, as we well know, a dollar was worth
much more than it is now. At most sites, there was no shortage of work to
be done, so computer time was a scarce and costly resource. This was one
of the factors which opponents of the early higher-level languages cited:
with machine time at a premium, the greater size of compiled programs,
often five to ten times bigger than an equivalent handcrafted machine
language program, was too wasteful. Of course, as the cost of machine
time fell relative to programmer time, the power of this argument
evaporated. But in the meantime, this scarcity and cost of machine time
was a driving force in the development of operating systems. Something
had to be done to reduce the time lost between programs, so that more work
could be pushed through the computer.
In 1953 at the Eastern Joint Computer Conference several users of the
IBM 701 met and discussed the need for some way to streamline the
scheduling of computer programs. This led to the first operating system,
a batch processing monitor program for the 701 written by programmers at
the General Motors Research Center in 1955. The electro- static memory of
the 701 was not very reliable, so IBM brought out the core memory 704 as a
replacement. The monitor was rewritten for the 704 as a joint effort by
General Motors and North American Aviation in 1956. Their GM/NAA I/O
System was further developed by the SHARE user group in 1960 as the SHARE
Operating System (SOS). Finally, IBM took over support of it, and, with
the name changed to IBSYS, it was widely used on the transistor
(second-generation) IBM 7090 and 7094 computers. It was not, however, the
only operating system for this family of computers. IBM had also
developed a FORTRAN monitor system (FMS), Bell Labs wrote a monitor called
BELLMON, and the University of Michigan Executive System (UMES) was used
at many universities.
These batch processing monitors made it possible to put a series of
jobs together on an input tape. The jobs were separated by simple control
cards, such as $COMPILE MAD or $DATA, to indicate functions to be
performed or the location of data. Time on the 7090 was frequently seen
as too valuable to be taken up with card processing or printing, so quite
often these tasks were handled by some smaller, cheaper computer,
typically an IBM 1401. The input job streams and card data were written
to tape on the 1401, and then the tapes were taken to the 7090. Output
was done in reverse: the 1401 received tapes from the 7090, and did the
printing or card punching. This arrangement was a good deal for the IBM
salesmen, because they got to sell (or lease) two computers instead of
one!
UNIVAC's announcement of the 1107 in December 1960 was very late. By
that time the first IBM 7090 had been in the field for a year, and over a
dozen more had been shipped since then, while the first Philco Transac
2000 and Control Data 1604 computers were installed in early 1960. The
announced delivery date for the 1107 was late 1961, but due to various
development problems, the first one was not completed until September
1962. To have any marketplace advantage at all, UNIVAC would have to
offer a superior product. The operating system software was one area in
which UNIVAC tried to do better.
UNIVAC's systems programming group in St. Paul started work on an
operating system for the 1107, which eventually became known as EXEC I.
It was intended to support true multi-programming: sharing CPU time among
several batch runs. This would permit the use of on-line utility programs
to do the card-totape and tape-to-print/punch work which the IBM 7090
sites were doing off-line. EXEC I was to be more sophisticated than batch
monitors, since it would schedule CPU time, allocate memory, and queue i/o
requests. Processing was interrupt- driven, using i/o completions or
clock timing, to force programs to relinquish control of the CPU. The
control algorithm was simple: each program was classified as either
compute-bound or i/o-bound, and the EXEC kept a first-in first-out queue
for each class. Each program execution within a run was scheduled
independently, so the programmer had to supply cards describing the
resources (core, tape, drum, reader, or printer) that it needed. These
statements were complex, making EXEC I difficult to use. Putting together
a whole runstream took a lot of work. EXEC I was written in the assembly
language (known as SLEUTH) of the 1107; it was 25,000 lines of code, and
occupied about 8K of the 1107's 32K of memory.
The early 1960s were a difficult time for Sperry Rand, and the
company did not have the resources to do all of its software development
in-house. For the 1107, UNIVAC wrote EXEC I and SLEUTH, but the ALGOL,
COBOL, and FORTRAN compilers were contracted out. The contract for COBOL
went to Computer Science Corporation (CSC), which had already produced a
FORTRAN compiler for UNIVAC's LARC computer and was also writing much of
the software for the UNIVAC III, the UNIVAC Philadelphia division's
business computing counterpart to the 1107. Very probably there was some
kind of barter involved, since CSC received the first 1107 shipped by
UNIVAC.
EXEC I wasn't ready yet, so CSC went ahead and devised its own
operating system for the 1107, which became EXEC II. CSC stretched the
terms of their contract a good bit: when the COBOL compiler was finished,
it was for an EXEC II environment, not EXEC I! CSC designed EXEC II to be
a serial batch processing system, with a multiprogram- ming capability
limited to the handling of card input and printer output. This still gave
it an edge over the IBM 7090 monitors, without introducing the
complexities of EXEC I. EXEC II made extensive use of the FH-880 drum for
staging card input and printed output, as well as for temporary storage of
program files read in from tape. Keep in mind that at this time disk (as
opposed to drum) technology was very new, and UNIVAC had no disks. Not
until 1970 was a disk drive, the 8414, supported on the 1100 Series. The
drums of the early 1960s did not have enough capacity to accomodate
long-term storage of program files. Therefore, programs were usually kept
on tape or card.
EXEC II was composed of resident routines which stayed in memory at
all times, and non-resident ones which were brought in from drum only when
needed. The resident routines included a minimal control card
interpreter, a jump vector for user program entries into EXEC II,
configuration tables, file directory handlers, and control routines for
drum, tape, and console. There was also a dispatcher routine to control
i/o queues. The major non-resident routines were the main control card
interpreter, job accounting, and the routines to control card and print
i/o. This last group of routines for card and print was called the
symbiont routines. In the later years of EXEC II, there were symbiont
routines for data interchange with remote or on-site UNIVAC 1004 or 9300
computers. The term symbiont referred to the symbiotic rela- tionship
between the computer's central complex and the peripheral devices.
EXEC II was bigger than EXEC I, comprising 45,000 lines of assembler
code and occupying 12K of memory. The command language was easier to use
than that of EXEC I, and was the basis for the Executive Control Language
(ECL) used in EXEC 8. The major difference in syntax is that in EXEC II,
the options field came first (immediately after the @) instead of after
the operation field. For example, a call to the COBOL compiler to compile
input source element BING, putting the updated source output in BONG and
the relocatable object output in TICK/TOCK would be:
@SX COB BING, BONG, TICK/TOCK
The S option said to punch the source output on cards and the X to abort
the compilation if errors were detected. Incidentally, the names BING,
BONG, and TICK/TOCK are taken from an example in the EXEC II Programmers
Reference. Many statements had essentially the same meaning in EXEC II as
they would have in EXEC 8, including:
RUN run initiation
FIN run termination
XQT program execution
MSG console message
ASG facilities assignment
PMD postmortem dump
ELT input cards into program file
HDG heading for print pages
EXEC II provided a tape file structure called a PCF (program complex
file) for source, relocatable, and absolute program elements.
Manipulation of program elements was done through a set of routines called
CUR (complex utility routines) which was the ancestor of EXEC 8's FURPUR
processor. CUR was called via an @XQT CUR, followed by directives on
subsequent cards. A few of the directives, such as ERS, FIND, and PCH
were carried over directly into FURPUR. Other processors which came with
EXEC II were:
ALG ALGOL Compiler
ASM Assembler (SLEUTH)
COB COBOL Compiler
FOR FORTRAN Compiler
LFT LIFT: a FORTRAN II to FORTRAN IV conversion routine
The ALGOL compiler was written at Case Institute of Technology, as part of
an arrangement whereby it received an 1107 to replace its old UNIVAC I.
As a result of its late appearance, only 36 1107s were sold, but
fortunately UNIVAC was prompt in announcing and delivering its third
generation 1108 computer. It was fully compatible with the 1107, so that
all the software, including EXEC II, could be carried over to it, and EXEC
II had several years of glory on the 1108. An article titled "Conversion
at Lockheed Missiles and Space" in the January 1967 issue of Datamation
said that Lockheed found that "The FORTRAN IV compiler and EXEC II
Operating System were considerably more powerful and of better design than
their counterparts on the IBM 7094." Using an 1107 as an interim machine,
Lockheed ultimately replaced two 7094s with two 1108s.
During its later years, there were two major enhancements to EXEC II.
The first was the capability to use a remote 1004 computer as an
input-output device. This was apparently the outgrowth of work done by
UNIVAC on one of the Bogart computers it made for the National Security
Agency. The second was the incorporation of the FASTRAND drum as a mass
storage device for permanent program and data files.
While both EXEC I and EXEC II were provided for the 1108, it was
clear that the two should be merged to provide a true multi-programming
system with the ease of use and external appearance of EXEC II. This was
EXEC 8. The specifications for it were drawn up in December 1964 and work
began in May 1965.
But that is another story. EXEC I and EXEC II were significant
developments in the evolution of operating systems. Though not as
sophisticated as the Master Control Program (MCP) for the Burroughs 5000
and the Compatible Time Sharing System (CTSS) developed at MIT for the IBM
7090, the EXECs did represent an advance over the batch moni- tors of
their time. They demonstrated that an operating system more complex than
the IBM monitors could achieve a high level of throughput.
Trademarks
Unisys, UNIVAC, FASTRAND, and UNISERVO are registered trademarks of Unisys
Corporation.
Editor's Note
Contributions of information are needed to keep this newsletter
going. This issue could not have been done without the EXEC II manuals.
I would like to do an issues on the UNIVAC III, the File Computer, and the
Burroughs 205 and 220, but I don't know enough about them. Please look in
your files or bookcases for material on them or any other old UNIVAC or
Burroughs computers. For this newsletter to continue, I need to have
input. Write to
George Gray
1418 Mackenzie Ct
Tucker, GA 30084
or call me at 404-656-7327 (daytime). Of course, articles such as the one
on UNIVAC in Pittsburgh in the first issue are always welcome. The next
issue will be in June.
Copyright 1993, by George Gray
--
___________________________________________________________________________
Randy Carpenter rcar...@gsu.edu % Got a light?
Georgia State University (404) 651-2648 No match.
Wells Computer Center %