Lecture 2
Computer History:
Relay and Valve
Computers
By
Dr Michael Freeman
Lecture Outline
Electro-mechanical computers
Relay computers
Valve computers
Case study 1: ENIAC
Case study 2: Manchester Mark 1
EDSAC Simulator
Konrad Zuse (1910 - 1995)
No significant attempts to
build a general purpose
computer were made after
Babbage’s death until the
1930’s.
The first examples were the
Z1 and Z3, discovered after
World War II.
Constructed in Germany
between 1936 - 1941.
Z1
Mechanical design, constructed from thin metal
sheets (30,000 parts).
Powered by an electric motor, used to provide a
clock frequency of 1Hz.
Z1
Number represented
in 22 bit binary
floating point format.
The AU was an
adder, and all of the
operations were
reduced to additions
or subtractions.
Z1
Programs were stored on punch tapes
using an 8-bit code.
Z3
Owing to reliability
problems with the
Z1, the Z3 was
entirely constructed
using relay
technology.
Programmed using
punched tape and
user console.
Relay Logic
AND Z = A&B
OR Z = A+B
NOT Z = A
FLIP FLOP
Z3
Instruction implemented
using a micro sequencer
constructed from
stepwise relays.
Instruction overlapping
used i.e. read next
instruction whilst writing
result.
Fast addition using carry
look-ahead circuit
constructed from relays.
Harvard Mark 1
The Mark 1 was developed by Howard Aiken
and built by IBM between 1939 - 1944.
Also known as the IBM Automatic Sequence
Control Calculator (ASCC).
Harvard Mark 1
Constructed from electromechanical relays, 55
feet long, 8 feet high, 2 feet deep, weighed 5 tons,
relatively slow and very noisy.
Numbers (23 decimal places) were stored
mechanically using 3000 electromagnetic decimal
storage wheels. It also had 1400 rotary dial
switches connected by 500 miles of wire.
The Harvard Mark 1 was used by the US Navy for
gunnery and ballistic calculations until 1959, but
was out of date by the time it was commissioned.
Harvard Mark 1
Went on to develop the Mark II, Mark III and
Mark IV computers using valve technology.
He also developed the concept of the Harvard
computer architecture.
Harvard Mark 1
The Harvard architecture uses physically
separate instruction and data memory.
Advantages:
?
?
This allows the next instruction to be read whilst the
previous calculations data is written to memory.
The width of the address and data bus can be
optimised to the required size.
Disadvantages:
?
?
Two memory modules are required.
Storing program data within the instruction memory
can be difficult.
Colossus
Colossus (1943) the first valve based
calculating machine.
Colossus
Thermionic diode and triode
valves.
Electrons emitted from the
cathode due to heating.
Diode (gate unconnected)
?
?
If anode - electrons repelled,
no current flows
If + electrons are attracted,
current flows.
Varying the gate voltage
produces a large variation in
anode current.
Valve Logic
NAND Z = /(A&B)
FLIP FLOP
OR Z = A+B
Colossus
An application specific computer designed for
code breaking, used more than 1,500 valves.
Coded messages were read in on paper tape at
5000 chars/sec using a photo-electric reader.
Simulated the Enigma’s rotors using a network
of valves.
Colossus was not programmable in the modern
sense, everything was hard wired.
Programmed to a limited degree by altering the
wiring via plug-boards and switches.
John Atanasoff 1903-1995
Helped develop the first
machine to demonstrate
electronic techniques in
digital calculation and to
use a regenerative
memory.
ABC
The machine was called the Atanasoff Berry
Computer (ABC) after its creators, Clifford Berry
and John Atanasoff.
An application specific computer designed to
solve large simultaneous linear equations,
constructed 1939-1942.
600 vacuum tubes:
? 300 in arithmetic unit: addition and subtraction
? 300 in control and memory
Used punched cards for input and output.
ABC
ABC
Capacitor memory: 30 numbers/drum (Abacii)
? Number = 50 bits (1500 capacitors/drum).
ENIAC
Electronic Numerical Integrator and Computer.
ENIAC
Commissioned by the U.S. Army to calculate
firing tables for specific weapons for a range of
environments and weather conditions.
ENIAC
ENIAC was completed in May 1944 and has a
strong claim to be the first ever general purpose
electronic computer.
Developed by a team lead by J.P.Eckert and
J.W.Mauchly.
Decimal computer, used more than 18,000
valves, 100 by 10 by 3 feet, weight 30 tons.
Faster than anything that had been built
previously; multiplication in under 3 ms.
Described as being “Faster than thought”.
ENIAC
Functional block diagram
ENIAC
Function tables constructed from banks of
decade switches; idea used in Harvard Mark I
ENIAC
Memory constructed from 20 electronic
accumulators (registers).
Each accumulator comprised of 28 valves,
capable of storing a signed 10 digit
decimal number.
ENIAC
ENIAC floor plan: 40 units, 3 function tables,
2 input / output units
ENIAC
ENIAC was NOT a “stored program” computer.
For each problem, someone analyzed the
arithmetic processing needed and prepared
wiring diagrams.
Process was time consuming and prone to
errors.
The main limitation of ENIAC was its inability to
switch from one program to another i.e. it was
hardwired.
ENIAC
This lead John Von Neumann and others
to develop the idea of storing the
programs within the computer’s memory.
The original idea was to allow the
computer to modify its own program i.e.
write its own new program.
This innovation is the major single factor
which allowed later computers to advance
beyond their contemporaries.
ENIAC
The architecture of a stored program
computer is commonly called a Von
Neumann architecture
ENIAC
The Von Neumann architecture uses the same
memory for instructions and data.
Advantages:
?
?
A single memory module can be used, minimising the
number of processor pins and buses.
Instruction and data are treated equally, allowing data
to be easily embedded into a program.
Disadvantages:
?
?
Doubles the memory bus’s bandwidth
The address and data bus size can not be optimised.
Manchester Mark 1
The first fully electronic binary computer to
execute a stored program.
Manchester Mark 1
Created at Manchester University during 19471949 by a team of people which included:
A.Turing, F.Williams, T. Kilburn and G.Tootill.
First machine was designed to test Williams’ idea
of storage based on cathode ray tubes.
CRT memory had a big advantage over existing
delay line memory, allowed fast random access to
short strings of bits i.e. 20-bit or 40-bit.
Manchester Mark 1
Bits were stored as very small areas of
electrical charge held on a phosphor coated
screen - refreshed every 1/5 sec.
Manchester Mark 1
Electrical pulses converted
to sound pulses and
transmitted down a long
tube of mercury.
Sufficient delay allowed a
number of bits of data to be
stored before first bit was
received and re-transmitted.
Disadvantages: slow, serial,
non random access
memory.
Manchester Mark 1
The first hard disk? MM1 had two magnetic
drums for backing store.
Relatively slow, but had 16 times the capacity of
the random access CRT store.
Manchester Mark 1
Memory was divided into pages.
A page was an array of 32 * 40 bits, the capacity
of a basic Williams-Kilburn Tube, and the unit of
magnetic drum storage.
4 pages of random access main store.
128 page capacity drum backing store.
Each 40-bit addressable line could hold one
40-bit number or two 20-bit instructions.
First to develop a paging type memory
architecture.
Manchester Mark 1
Functional block diagram
Used more than 4000 valves
Manchester Mark 1
The successful operation of the WilliamsKilburn CRT store was one of the key
factors which led to the Manchester group
being the first to build a stored-program
computer.
EDSAC
Electronic Delay Storage Automatic Calculator (1949)
EDSAC
Can be argued that this computer was really the
first machine to execute a stored program.
Based on EDVAC, a computer developed at the
University of Pennsylvania (ENIAC).
Memory was constructed from mercury delay
lines called long lines.
Had 32 long lines each capable of storing 32
words of 18 bits i.e. 1024 words.
Also used smaller delay lines for registers called
short lines, storing only a few bits of data.
EDSAC
Functional block diagram
EDSAC
Operation were represented by letters e.g.
A = add, S = subtract etc.
Instructions written in symbolic form and then
translated into machine code.
Simplified by using the same alphanumeric code
for both data and operations.
Short 17 bit and long 35 bit integers and
fractions signified by the letters F and D.
EDSAC
EDSAC simulator
http://www.dcs.warwick.ac.uk/~edsac/
EDSAC
Hello world program
Assembly directives
?
?
?
TmK sets the load point to m
GK set the @ parameter to current
load point
EZPF enter the program at
location @
‘Z’ stops processor
‘O’ outputs character at location
m+@
First Generation Computers
ENIAC, MM1 and
EDSAC are classified
as first generation
computers and share
a similar system
architecture.
First Generation Computers
Internal structure of a
typical first generation
computer : IAS
computer designed by
J. von Neumann.
Lecture Summary
First generation computers:
?
?
?
?
?
1940 – 1954.
Used electro-mechanical, thermionic valve
technologies: relays, triodes, diodes etc.
Stored program machines.
Programmed using low level languages: machine
code, symbolic languages etc.
Simple control, arithmetic, memory architecture.
Two main computer architectures:
?
?
Von Neumann.
Harvard.