FEATURE / ANALYSIS
pavedthewayforcomputerdevelopment
to begin, as it provided this instant switching
ability, but these days the transistor has taken
on this role.
In both instances, the crucial ability is that an
input signal can control the flow of electricity
through another part of the circuit. In the case
of valves, it’s the control grid that controls the
flow between the anode and cathode, and
for transistors the base controls, the flow
between the collector and emitter.
The development of the processor
On their own, neither a valve nor a transistor
is all that much use for our Boolean algebra,
but just stringing two together can provide us
with a simple logic circuit. Connect the emitter
from one transistor to the collector of another
and you now require both base pins to be set
to a high voltage in order for current to flow
throughbothtransistors.Theresultis known
as an AND gate (for obvious reasons) where
the output is only a logical 1 when both inputs
are also set to 1.
Now, even the very most rudimentary
explanation of how a CPU functions on a
Boolean function level or transistor level
would take the entire rest of this feature, so at
this point we’re going to skip over quite a few
steps. There’s a vast field of computer science
between the development of simple circuits
involving a few valves to creating a modern
CPU that houses billions of transistors in a
package the size of your thumbnail. You’ve
got the development of the full spectrum of
logic circuits – such as the NAND gate that
gives NAND flash storage its name – then
there’s the development of the transistor
itself, initially in its discrete form then in
integrated circuit form.Instead, let’s skip to where we’ve
developed some sort of CPU that can take a
number of inputs from some sort of memory
(whether the memory is electronic or holes
in a cardboard punch card) and output the
results we want.Bits and bytes
Processors are finite machines. They’re
physical objects with a limit on how much
information can be fed in or out of them: at a
transistor level you can’t just throw together
two enormously long numbers and add them
together, as you theoretically could on a piece
of paper. Instead, we need to break those
numbers – or whatever other information
those numbers represent – into chunks (or
words) that are small enough for our system
to be able to handle.
Modern-day processors generally work
with numbers up to 64 bits in size, meaning
the largest integer (whole) number that can
be represented, or the largest single piece of
data that can be transferred from memory in
a single operation is 64 bits in length. Now, a
64-bit number is very large – it’s a 19-digit-
long number even in decimal – but computers
can also work on much smaller spans of data.
For the sake of explanation, we’ll look at a
system working in a word size of eight bits.Colossus is regarded as the first programmable,
electronic, digital computer, with x valves used
to perform its Boolean operationsTwo transistors connected in series can be used to create an AND gate,
where both inputs need to be set high for the output to be set high
OutputInputAInputBTO SOLVE THIS PROBLEM, A
FURTHER WIRE IS ADDED THAT
PROVIDES A REGULAR CLOCK
SIGNAL THAT TICKS ON AND OFF