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Introduction
Please forgive me if I totally ignore earlier machines made by:
Here is a list of vacuum tube computers.
We are so spoiled by our modern computer technology, speed, storage, reliability, and price
We are familiar with living with computer technology now - cheap, fast, cool, small, user friendly, ...
I know only two people who worked on regular (parallel word fetch and add) vacuum tube machines -
In college I got to play with an
LGP-30
which had only 113 vacuum tubes and some 1,500 solid state diodes.
Because it was bit serial, registers on the drum, (making it a great deal slower, cooler,
cheaper (only $50,000 1958 dollars), and more reliable)
it really doesn't count. But you got the flavor -
Frieden Flexowriter
capable of paper tape input and output.
The usual comparison - between early and current computers -
With such difference as stated above - you might expect living with a "THEN" computer
would be very different than a "NOW" computer ;-)
Where to start?
Folks justifiably considered vacuum tubes "unreliable". Lets assume the mean time to failure
of a tube in that service was 5 years or about 1800 days. If you had a computer with
1,800 tubes you could be led to expect a tube failure about every day. A major inconvenience
even if instant repair.
Computer designers were well aware of the above problem, and tried to increase the reliability
of their computers by many means:
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Living with Vacuum Tube Computers
Under development June 23, 2013
needs amplification and checking by Bob Erickson and LaFarr Stuart
Dear Friends
- but what about then ??
- Bob Erickson, repaired an
IBM 701
also at
Los Alamos National Lab
- LaFarr Stuart, wrote assembler (in hex) for
Iowa State "Cyclone",
also
an IAS machine
Item Computer "Then" - early 1950s
Computer "Now" - 2010
Cost About 30 houses
1/2 a monthly rental for apartment or house
Size Most of a specially cooled room
Small table or pocket
Watts About 20 electric stoves full on
About a flashlight
Input Paper tape or IBM cards
Voice, touch screen, keyboard, camera
Output Paper tape or printer
Speaker, color video, color printer
Memory Less than a page of text
A feature length movie, in color
"User friendly" No way
Punch request into paper tape or card
Load and run the job,
Feed request into computer
Unbelievable, Example
www.freemake.com/blog/ "Just ask Siri"
Speed Add 10,000 numbers/second
- Don't ask, Number too big to think about
Repair Maybe every other day
Need maintenance person/staff on site
Goes out of style first
What is maintenance ?
Programming On-site staff of experts
Buy an ap, cost of cup of coffee
Technology Vacuum Tube
Size - 1/2 hot dog
Transistor
Size - Can't see it
Procurement
Big deal contract, wait months -
- or -
"Roll your own",
- and hire architect & techies - wait years -
Time to install special floor, electric power,
cooling, maintenance room, train staff
Walk into store, or mail order
you applied voltages
rather slowly ( over a minute )
to gently increase the temperature of
the thousands of filaments and cathodes getting red hot.
On the Cyclone, you could hear the motor driven
VARIACs
ramping up the voltages.
Then it got moved to Aberdeen Proving Ground - and those people complained bitterly
about the many vacuum tube failures each time they turned the machine "ON".
The Moore School people were appalled "You mean you turn it OFF ??????"
"My" LGP-30's drum got badly scratched because someone turned it on again too soon
after it was turned off :-((
- to permit "Margin Testing" to run test programs under marginal conditions
- searching for marginal circuits (tubes) to be replaced before failing under customer usage.
Vacuum tubes enabled AM radios in the early 1900s. In the mid 1930s the
All American Five radio
became a cheap popular radio, not even using a power transformer. It, like many others,
drove the tubes hard to get maximum output for minimum cost. Approximately once a year
a tube failed. Not knowing which, the filaments were in series,
you took the tubes to your local drug store, tested them,
bought a replacement for the failed tube - and life was good again. :-))
- Buy "premium" tubes of better design, materials, manufacture, testing, ...
- Do not drive tubes hard or make them overheated
- Turn tubes "ON" and "OFF" gently, and not very often
- Use circuits rather tolerant of "weak" tubes
- Enabling voltage margin testing to identify "weak" tubes.
There is an effect in manufactured goods that new items
have a higher failure rate until used for a while, or "burned in". Most computer people
had racks where tubes were heated and current drawn for several weeks then
tested for performance before being made available for insertion into the computer.
This helped reduce "infant mortality" in service.
In radio service small vacuum tubes conducted anode current all the time, in varying quantities.
In computer service the tubes were logic elements - either "ON" (conducting)
or "OFF" (not conducting). After some puzzling failures, it was discovered that some tubes
would not conduct well after long periods of being "OFF" - maybe in a run/stop flipflop.
Item 1,
Item 2
Further research indicated that cathodes with appreciable silicon tended to "Sleeping Sickness".
Reducing the silicon in the cathodes reduced this problem.
- A Register - most arithmetic and compare
- Q Register - multiply, divide, shift
Visible at console to operator/repair/program-debugger
- A & Q Registers, Instruction Register, Program counter, status bits
This means you *HAD* to use self modifying code to make a loop.
To move a string of characters, say in an assembler to a symbol table,
- you had to modify both the source and destination address in the instructions.
- on some, the divide was for positive integers only
- a compare for equality took a subtract
- - and then see if sign changed
when subtracting one from result -
Think of using that when writing your assembler :-((((((
In one of the world's paradoxes,
- flaky Williams tube memories were never given parity checking
- reliable Core memories (developed years later) almost always had parity checking
Go figure -
- not even a console typewriter - expensive, hard to interface, failure prone -
The Frieden Flexowriter
became popular, reliable typing, and punching/reading paper tape at 10 characters/second.
- not enough memory for an "operating system" - yet to be invented
Started June 22, 2013