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-> My History
Computers I Have Worked With
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The GIER computer was built by the long-departed
Danish computer manufacturer RegneCentralen. In those days,
computers were large and hand-built in small numbers for
lots of money. The GIER was considered very successful.
I think they built about 40 of them over a 6-year period.
I did not actually get my hands on these until 1970, when
I enrolled at University of Copenhagen, where the Math department had
two in their basement, and the Niels Bohr Institute of Physics
had another one.
- RC-GIER - Designed 1960, I used it 1969-1971.
- IBM 7094 - Designed 1960, I used it 1970-1973.
- RC-4000 - Designed 1965, I used it 1969-1970.
- IBM 360 - Designed 1965, I used it 1970-1973.
- IBM 1130 - Designed 1968, I used it 1970-1972.
- Univac 1100 series - Designed 1965, I used it 1970-1980.
- CDC 6500 - Designed 1968, I used it 1972-1974.
- PDP-11 - Designed 1970, I used them 1974-1983.
- VAX Family - Designed 1975, I used them 1980-1995.
- Sun 3 - Designed 1980, I used them 1990-1997.
- Apple 68000 MacIntosh - Designed 1985, I still use them.
- Sun 4 (SPARC) - Designed 1987, I used them 1991-1998.
- Intel x86 Family - Designed 1985, I still use them.
The GIER machines were compact and handsome for their time.
The cabinet was about 200 cm high (6.5 feet), 220 cm (just over 7 feet)
long and about 60 cm (2 feet) deep. The two broad sides each had
3 sliding teakwood panels, the ends were a light gray-brown enamel,
and off to one side was a desk console with a high-speed papertape reader
(2000 cps, optical) to the left, a slanted bakelite panel with lights,
switches and a loudspeaker to the right, and an electric typewriter
in the middle.
The machines had 42-bit words (40 bits of arithmetic precision and
two "flag bits"). They had 1024 words of this, with an optional
4096 additional words of "buffer memory" which could not be
directly addressed, but could be block copied in and out of
main memory. They also had a magnetic drum with 960 tracks,
each of which could hold 40 words. This adds up to about 200
kilobytes of storage. Amazingly, they packed onto that drum
a small operating system, an Algol-60 compiler and a runtime library
with virtual memory management (for code segments only).
The machines were quite usable, and were used both for undergraduate
instruction in computer programming and for many research
projects including weather modeling.
For its time, this was a supercomputer. IBM donated one to the Technical
University in Copenhagen, where it served as the Campus Computing resource,
and also made time available to other universities. This machine had
36 bit words, and I think 32 K words of main memory. The machine was very
fast: Only about 3 microseconds per instruction, so rather than let
the machine read punched cards and write to the printer, all the jobs and
data were read onto magnetic tape and then the output was written to
tape. The conversions between tape and paper or cards were done on
an IBM1401, which was later replaced with an IBM-360/30 which could
accept jobs remotely via modems.
The operating system of the 7094 was called IBSYS and lived on a tape drive.
It had many compilers, including Fortran II, Fortran IV and COBOL.
(A reference manual for the very similar IBM 7090 is
here - PDF, 156 pages).
The RC-4000 was the successor to the GIER, but had nothing in common with it.
It was a 24-bit machine with a real-time operating system that had
interrupts, memory protection and a limited amount of multi-tasking.
It was used for many interesting applications, including real-time
chemical process control, large databases (telephone directory
call-centers) and time-sharing. The operating system was the subject of
a fair number of computer science research journal articles, and
many of the concepts embodied in it were absorbed into Multics and Unix.
The one we used at Univeristy of Copenhagen belonged to the Chemistry
department, but time-sharing terminals were found all over the science
campus section, where they served other departments until the Univac 1106
The IBM-360 family of computers ranged from the model 20 minicomputer
(which typically had 24 KB of memory) to the model 91 supercomputer
which was built for the North American missile defense system.
Despite their differences, all these machines had the same user instruction
set; on the smaller machines many of the more complex instructions were
done in microcode rather than in hardware. For example, machines in the
lower midrange did not have multiplier hardware, but the microcode
implemented multiplications by repeated addition. It was rumored
that the smallest machines did addition by repeated increments!
The machines had different operating systems. The smallest machines
could not really support an operating system and were often used
for specialized applications, where a program was loaded from binary
punched cards at startup. The middle range used a system called
DOS (not related to MS-DOS) and the higher end system was called
OS/360. These were the machines that established 32 bits as the
standard for computers.
The first IBM-360 I used in Copenhagen was the spooling front-end for
the 7094. In 1970, the technical university installed a 360/65, later
upgraded to a 360/75. When it came in, it had 1 MB of RAM (magnetic core
memory in those days) and a roomful of disk drives, probably adding up
to about 200 MB.
Today's S/390 mainframes are direct descendants of the IBM-360
The IBM-1130 was a mini-computer built in the shape of a desk.
The ALU had 16-bit words, and it came with a 1.5 MB hard disk.
The DOS had a Fortran-IV compiler, but even though the machine
was similarly sized to the GIER, it was much less usable.
Eventually, the Niels Bohr Institute decided that it could be used as
remote job entry terminal to the IBM computers at the technical university.
More about the IBM-1130 at
Howard Shubs' web site.
The Danish universities decided to install 3 large computers at the three
largest univerities, an they wisely chose to get an IBM, an UNIVAC and a
Control Data. University of Copenhagen got the Univac, and it was a great
When the machine was installed, it was a Univac-1106 with 131 K words
(of 36 bits), i.e. about 600 KB. About 18 months later, it was upgraded
to an 1108 which ran twice as fast. This upgrade consisted in replacing a
divide-by-two flip-flop in the system clock circuit by a jumper.
We also got more memory, I think we doubled it.
This machine served an endless stream of batch jobs from both local
and remote card-reader/printer stations plus about 50 interactive
Digital Equipment Corporation's PDP-11 family of minicomputers was
extremely successful for over 25 years - for good reasons.
The instruction set was elegant and flexible, the engineering design
was modular in ways
that not only allowed the manufacturer to custom build machines
of many different price/performance levels, but also allowed
users to expand them in the field later. Machines existed in all
differnet sizes; towards the end of its lifespan, the range spanned from
personal computers built into a terminal, to time-sharing multiuser systems
capable of serving as a common computing resource for an entire
Read more on my PDP-11 page.
The PDP-11 address space eventually became too small to do practical
work: As the machines got less expensive, people were attacking more
complex problems, requiring larger programs. So Digital Equipment
built a larger machine, called VAX-11 (Virtual Address eXtensions for
pdp-11). This machine was the best design I have ever worked on.
The instruction set was very powerful, although some thought it was
too large to be truly elegant.
Read more on my VAX page.
When I changed employers in 1990, one of the attractions of the new
job was that instead of a text terminal connected to a central computer
cluster, this company put a workstation with a bit-mapped windowed
display on the desk of each engineer. In those days, that would be
a Sun Microsystems Sun-3/80.
Sun Microsystems was a company built on the discovery that single-chip
microprocessors had become powerful enough that one could build a general-
purpose computer around one of these chips, powerful enough
to tackle the same class of problems that one would have done on a
mainframe or a VAX, but inexpensive enough to give one for the exclusive
use of a scientist or engineer. Programmers loved them. They ran the same
Unix systems that was used on many PDP-11 or VAX sites, were programmed in
the "C" programming language, and on the windowed screen you could have
5 or 6 windows, each looking like a terminal and switch your keyboard
back and forth between them.
My new employer built communications equipment around the same family of
Motorola microprocessors, and we used the compilers and other software
development tools of the Sun machines.
The MacIntosh took the ideas behind the Sun and applied them to systems
more suited to consumers: Half the price, and as easy to use as possible.
The MacIntosh did not "invent" or even popularize the mouse: The Sun had
new was the desktop metaphor as a way of organizing the
workspace, and the removal of command lines: Clicking on the pictures
was the ONLY way to run programs.
I loved the Macs from I first saw one, but I thought this was way too
much money to spend on a toy.
My wife and I bought one in 1989, when a brother-in-law who managed a
computer store got a good offer for a demonstration system, which he
passed along to us. Our machine was called the Mac SE; it had one MB
of DRAM and a 20MB hard drive, and cost USD 2000.
Ironically, one of the things that I found attractive about it was
the knowledge that programming for the Mac was very difficult, and
the machine did not come with any compiler or other programming tools.
Thus I was guaranteed not to be tempted into spending all my spare time
playing with the computer, but would be able to enjoy it as a tool.
The MC68000 was a nice enough CPU, but Sun Microsystems decided
they could build a much more powerful system for not much more
money by designing their own CPU according to the "RISC"
(Reduced Instruction Set Computer) architecture fashion of the time.
Sun called their RISC design SPARC (which they said stood for something
Sun Processor Architecture for RISC Computing).
The idea behind RISC was to
make the instructions simple enough that every instruction could
complete in one cycle of the master clock. You might execute a few
more instructions that way, but since the CPU logic would be simpler,
you could use the circuitry space that was saved on the CPU
chip to include a larger cache memory, so fewer of the instructions
and data fetched from memory would have to come from the main
memory. This would allow the programs to run faster.
In general, RISC computers were unfriendly to programmers that
wanted to write "assembly language" where the programmer has
to describe the operations in terms of individual machine
instructions. But most programmers very rarely do that.
So with a good C compiler, the "weird" instruction sets did
The first SPARC machines came out around 1989 and allowed
Sun to build larger servers to complement their desktop machines.
Within 2-3 years, a smaller, less expensive RISC CPU was replacing
the MC68000 chips in the desktop workstations.
The Intel 8088 microprocessor was chosen by IBM for their first
Personal Computer in 1980. Soon many manufacturers were building
very similar machines, using also the slightly faster 8086 and 80186
CPU versions. Around 1982, the PC-AT (advanced technology) came out
with the 80286 CPU.
After interesting video games became available (beginning with
the Microsoft Flight Simulator) every manufacturer had to make
their machine indistinguishable from the PC-AT in order that
it would be able to run these games. Soon the intense competition
among the smaller manufacturers in Taiwan drove the prices of the
look-alike "PC clones" well below the price of "real" PCs, and
the market really took off.
After the MacIntosh stunned the market, IBM and Microsoft worked
feverishly to produce a "Windows program" for PCs, and after several
very bad versions, Microsoft Windows version 3.1 finally became
a good enough imitation around 1990.
Meanwhile, Intel kept producing faster and better microprocessors,
still compatible with the 8088/8086/80286 series, although
the later versions beginning with 80386 also had a newer
memory management system that allowed them to run Unix.
Beginning around 1988, Unix was ported to 80386 PCs.
Today, PCs range from small portable ("laptop") computers to large
server machines with 4-way multiprocessor CPU sets and can run
any of these operating systems (plus several less common):
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