110 OCTOBER 2019|COMPUTERSHOPPER|ISSUE 380
at the development of acomplete
computing device and one that, had it
ever been completed, might just have
brought about asteampunk revolution.
Taking abroad view of the Analytical
Engine,itreally wasn’t toofar removed
from that of modern-daycomputers,
except that it employed cogs and gears
instead of transistors. Indeed, the
overview given by Doron Swade,a
historian of computing specialising in
the lifeand work of Charles Babbage,
will surely strike achord with those
who take an interest in such things.
“Babbage’s designs forhis Analytical
Engine describe ageneral-purpose
programmable digital computer that
embodies in its mechanisms just about
all the logical features of amodern
digital electronic computer.Atan
operational level, the Engine was
capable of conditional branching,
iterative looping, microprogramming
and parallel processing using multiple
processors, though neither Babbage
nor his contemporaries used these
anachronistic terms,”Swade explains.
“The Engine featured the separation
of the store (memory) from the mill
(central processor), and used aserial
fetch-executecycle and, in doing so,
anticipating the architecture that has
dominated electronic computer design
since 1945, when John von Neumann
published his seminal paper.”
Where the Analytical Engine would
have differed, however,isinits speed of
operation, as Martin Campbell-Kelly,
Emeritus Professor of Computing at
Warwick University and the editor
ofThe Collected Works of Charles
Babbage,admits.
“The Analytical Engine would have
performed not more than half-a-dozen
arithmetic operations aminute,”
according to Campbell-Kelly.
TAKE YOUR TIME
Swade reveals that some instructions
would have been much slower still.
“The Engine was capable of double-
precision arithmetic, meaning it could
operateontwo 50-digit decimal
numbers to produce 100-digit results,
but a50-digit multiplication would
take about three minutes.”
Given this somewhat pedestrian
performance,many thousands of times
slower than even the first electronic
programmable computers in the 1940s,
it’s appropriatetoquestion, despiteits
ingenuity,whether the Analytical
Engine could ever have done anything
useful. Both our experts envisaged that
it could have reaped benefits in science,
maths, engineering and astronomy; it
would still have been much faster than
human calculation, especially since its
programmable nature meant that it
could work unsupervised.
MISSING LINK 2: ELECTRONICS
There’sno denyingthatthe factthatat the
timethere were noelectronics–which only
came intobeingwith the inventionof the
triode valve,orthe Audion as he calledit, by
LeedeForest in 1906–wouldhavebeen a
major hindrance to the furtherdevelopment
of Babbage’sAnalytical Engine,had itever
been built. Indeed, this conclusion was drawn
by boththeexpertswe’vequotedonthe
possibility of Victorian computing.And without
electronics,the fastest we’d haveevergot
would havebeen about 200 instructions per
minute, the pinnacle of performanceachieved
mechanically.Orwould it?
In this feature we’ve considered the
mechanical computerand the electronic
computer,butwe’veignoredthepossibility
of anintermediateelectromechanicalmachine.Andit’shere
that we should introduce the relay, which,itappears,was
independently invented by JosephHenryandEdward Davyin
Like the triodevalve and the transistor that
supersededit, the relayallowed the flowof an
electrical current in one circuit to becontrolled
by acurrentflowinginanothercircuit.This
switching function is fundamental to logic
gates and, hence,toelectronic computers.
Where therelaydiffersfromthevalveor
the transistor,however,isthatit’san
electromagnetic device rather than apurely
electronic one.Forthisreason,it wasalot
slower.It’s not clear how fast these original
relays could switch, butmost of today’srelays
haveamaximumswitchingspeedof 5-10ms, so
they’d have permitted aclock speed of 100-200Hz.
While this is alot slower than even the firsttransistors,we
shouldn’t lose sightof how much fasterthis is thanthe mechanical
elementsin Babbage’s computing engines.
⬆Building on his
earlier Difference
Engine,pictured
here,Babbage’s
Analytical Engine
would have
been built from
cogs, gears and
mechanical linkages
⬅Lee de Forest’s invention of the triode valve came too
latetobring electronics to the Victorians and, with it,
the promise of high-speed computation
Ph
oto
:C
ars
ten
Ull
ric
h
1835, andby Samuel Morse in1840.
