our last episode brought us the star of
the 20th century were early
special-purpose computing devices like
tabulating machines were a huge boon to
governments and business aiding is
sometimes replacing wrote manual tasks
but the scale of human systems continued
to increase at an unprecedented rate the
first half of the 20th century saw the
world's population almost double world
war 1 mobilised 17 million people and
world war ii involved more than a
hundred million global trade and transit
networks became interconnected like
never before and the sophistication of
our engineering and scientific endeavors
reached new heights
we even started to seriously consider
visiting other planets and it was this
explosion of complexity bureaucracy and
ultimately data that drove an increasing
need for automation and computation soon
those cabinet sized electromechanical
computers grew into room size behemoths
that were expensive to maintain and
prone to errors and it was these
machines that would set the stage for
future innovation
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one of the largest electromechanical
computers built was the Harvard mark one
completed in 1944 by IBM for the Allies
during World War two it contains 765,000
components three million connections of
500 miles of wire to keep its internal
mechanics synchronized it used the
50-foot shaft running right through the
machine driven by a five horsepower
motor one of the earliest uses for this
technology was running simulations for
the Manhattan Project the brains of
these huge electromechanical beasts were
relays electronically controlled
mechanical switches in a relay there is
a control wire that determines whether a
circuit is opened or closed the control
wire connects to a coil of wire inside
the relay when current flows through the
coil an electromagnetic field is created
which in turn attracts a metal arm
inside the relays snapping it shut and
completing the circuit you can think of
a relay like a water faucet the control
wire is like the faucet handle open the
faucet and the water flows through the
pipe close the faucet and the flow of
water stopped relays are doing the same
thing just with electrons instead of
water the controlled circuit can then
connect to other circuits or to
something like a motor which might
increment account on a gear like in
Hollerith tabulating machine we talked
about last episode
unfortunately the mechanical arm inside
of a relay has mass and therefore can't
move instantly between open and closed
States a good relay in the 1940s might
be able to flick back and forth 50 times
in a second that might seem pretty fast
and it's not fast enough to be useful at
solving large complex problems the
Harvard mark one could do three
additions or subtractions per second
multiplications took six seconds and
divisions took 15 and more complex
operations like a trigonometric function
could take over a minute in addition to
slow switching speed another limitation
was wear and tear anything mechanical
that moves wear over time
some things break entirely and other
things start getting sticky slow and
just plain unreliable and as the number
of relays increases the probability of a
failure increases too the Harvard mark
one had roughly 3,500 relays even if you
assume a relay has an operational life
of 10 years this would mean you would
have to replace on average 140 relay
everyday that's a big problem when
you're in the middle of running some
important multi-day calculation and
that's not
all engineers had to contend with these
huge dark and war machines also
attracted insects in September 1947
operators on the Harvard mark to board a
dead moth from a malfunctioning relay
Grace Hopper who we'll talk more about
in a later episode noted from then on
when anything went wrong with a computer
we said it had bugs in it and that's
where we get the term computer bug it
was clear that a faster more reliable
alternative to electromechanical relays
was needed if computing was going to
advance further and fortunately that
alternative already existed in 1904
English physicist John Ambrose Fleming
developed a new electrical component
called a thermionic valve which housed
two electrodes inside an airtight glass
bulb this was the first vacuum tube one
of the electrodes could be heated which
would cause it to emit electrons a
process called thermionic emission the
other electrode could then attract these
electrons to create the flow of our
electric faucet but only if it was
positively charged if it had a negative
or neutral charge the electrons would no
longer be attracted across the vacuum so
no current would flow an electronic
component that permits the one-way flow
of current is called a diode but what
was really needed was a switch to help
turn this flow on and off luckily
shortly after in 1906 american inventor
lee deforest
added a third control electrode that
sits between the two electrodes in
flemmings design by applying a positive
charge to the control electrode it would
permit the flow of electrons as before
but if the control electrode was given a
negative charge it would prevent the
flow of electrons so by manipulating the
control wire one could open or close the
circuit it's pretty much the same thing
as a relay but importantly vacuum tubes
have no moving parts this meant there
was less wear and they could switch
thousands of times per second these
triode vacuum tubes will become the
basis of radio long-distance telephone
and many other electronic devices for
nearly half a century I should know here
that vacuum tubes weren't perfect
they're kind of fragile can burn out
like light bulbs but they were a big
improvement over mechanical relays also
initially vacuum tubes were expensive a
radio set often used just one but a
computer might require hundreds or
thousands of electrical switches but by
the 1940s their cost and reliability had
improved to the point when they became
feasible for use in computers at least
by people with deep pockets
like governments this marked the shift
from electromechanical computing to
electronic computing let's go to the
thought-bubble
first large-scale use of vacuum tubes
for computing was the Colossus mark one
designed by engineer Tommy flowers and
completed in December of 1943 the
Colossus was installed at Bletchley Park
in the UK and helped to decrypt Nazi
communications this may sound familiar
because two years prior Alan Turing
often called the father of computer
science had created an electromechanical
device also at Bletchley Park called the
bomb it was an electromechanical machine
designed to break Nazi Enigma codes but
the bomb wasn't technically a computer
and will get 2 L Insurance Contributions
later anyway the first version of
Colossus contained 1600 vacuum tubes and
in total 10 colossi were built to help
with code breaking Colossus is regarded
as the first programmable electronic
computer programming was done by
plugging hundreds of wires into plug
boards sort of like old school telephone
switchboards in order to set up the
computer to perform the right operations
so while programmable it still had to be
configured to perform any specific
computation enter the electronic
numerical integrator and calculator or
ENIAC completed a few years later in
1946 at the University of Pennsylvania
designed by John Merkley and J presper
eckert this was the world's first truly
general-purpose programmable electronic
computer ENIAC could perform 5,000 10
digit additions or subtractions per
second
many many times faster than any machine
that came before it
it was operational for 10 years and it's
estimated to have done more arithmetic
than the entire human race up to that
point but with that many vacuum tubes
failures were common and ENIAC was
generally only operational for about
half a day at a time before breaking
down thanks thought-bubble
by the 1950s even vacuum tube based
computing was reaching its limits the
u.s. air force's ANF sq7 computer which
was completed in 1955 was part of the
sage air defense computer system which
we'll talk about more in a later episode
to reduce cost and size as well as to
improve reliability and speed a radical
new electronic switch was needed in 1947
Bell laboratory scientist John Barden
water Britain and William Shockley
invented the transistor
and with it a whole new era of computing
was born the physics behind transistors
is pretty complex relying on quantum
mechanics so we're going to stick for
the basics a transistor is just like a
relay or vacuum tube it's a switch that
can be open or closed by applying
electrical power wire control wire
typically transistors have two
electrodes separated by a material that
sometimes can conduct electricity and
other times resist it a semiconductor in
this case the control wire attaches to a
gate electrode by changing the
electrical charge of the gate the
conductivity of the semiconducting
material can be manipulated allowing
current to flow I'll be stopped
like the water faucet analogy we
discussed earlier even the very first
transistor at Bell Labs showed
tremendous promise it could switch
between on and off states 10,000 times
per second
further unlike vacuum tubes made of
glass and we've carefully suspended
fragile components transistors were
solid material known as a solid state
component almost immediately transistors
could be made smaller than the smallest
possible relays or vacuum tubes this led
to dramatically smaller and cheaper
computers like the IBM 608 released in
1957 the first fully transistor powered
commercially available computer it
contained three thousand transistors and
can perform 4,500 additions or roughly
80 multiplications or divisions every
second
IBM soon transitioned all of its
computing products to transistors
bringing transistor based computers into
offices and eventually homes today
computers use transistors that are
smaller than 50 nanometers in size for
reference a sheet of paper is roughly a
hundred thousand nanometers thick and
they're not only incredibly small
they're super fast they could switch
States millions of times per second and
can run for decades a lot of this
transistor and semiconductor development
happened in the Santa Clara Valley
between San Francisco and San Jose
California since the most common
material used to create semiconductors
is silicon this region soon became known
as Silicon Valley even William Shockley
moved their founding Shockley
semiconductor whose employees later
founded Fairchild semiconductors whose
employees later founded Intel the
world's largest computer chip maker
today ok
so we've gone from relays to vacuum
tubes to trend
sisters we can turn electricity on and
off really really really fast but how do
we get from transistors to actually
computing something especially if we
don't have motors and gears that's what
we're going to cover over the next few
episodes thanks for watching see you
next week crash course computer science
is produced in association with PBS
Digital Studios at their channel you
could check out a playlist of shows like
brain craft community and PBS infinite
series this episode was filmed at the
chad and stacey emigholz studio in
indianapolis indiana and it was made
with the help of all these nice people
and our wonderful graphics team is
thought cafe thanks for the random
access memories I'll see you next time
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