Hardware
The motherboard is the main circuit board inside
the PC which holds the processor, memory and expansion slots and connects
directly or indirectly to every part of the PC. It’s made up of a chipset
(known as the ‘glue logic’), some code in ROM and the various interconnections
or buses. Wide, high-speed buses are
difficult and expensive to produce: the signals travel at such a rate that even
distances of just a few centimetres cause timing problems, while the metal
tracks on the circuit board act as miniature radio antennae, transmitting
electromagnetic noise that introduces interference with signals elsewhere in
the system. For these reasons, PC design engineers try to keep the fastest
buses confined to the smallest area of the motherboard and use slower, more
robust buses, for other parts.
The processor (really a short form for
microprocessor and also often called the CPU or central processing unit) is the
central component of the PC. It determines, at least in part, which operating
systems can be used, which software packages the PC can run, how much energy
the PC uses, and how stable the system will be, among other things. The
processor is also a major determinant of overall system cost: the newer and
more powerful the processor, the more expensive the machine will be.
When the Hungarian born John von Neumann,
first suggested storing a sequence of instructions - that’s to say, a program -
in the same memory as the data, it was a truly innovative idea. That was in his
‘First Draft of a Report on the EDVAC,’ written in 1945. The report organised
the computer system into four main parts: the Central Arithmetical unit, the
Central Control unit, the Memory, and the Input/Output devices.
Today, more than half a century later,
nearly all processors have a ‘von Neumann’ architecture.
The underlying principles of all computer
processors are the same. Fundamentally, they all take signals in the form of 0s
and 1s (thus binary signals), manipulate them according to a set of
instructions, and produce output in the form of 0s and 1s. The voltage on the
line at the time a signal is sent determines whether the signal is a 0 or a 1.
On a 3.3-volt system, an application of 3.3 volts means that it's a 1, while an
application of 0 volts means it's a 0.
Processors work by reacting to an input of
0s and 1s in specific ways and then returning an output based on the decision.
The decision itself happens in a circuit called a logic gate, each of
which requires at least one transistor, with the inputs and outputs arranged
differently by different operations. The fact that today's processors contain
millions of transistors offers a clue as to how complex the logic system is.
The processor's logic gates work together to make decisions using Boolean
logic, which is based on the algebraic system established by mathematician
George Boole. The main Boolean operators are AND, OR, NOT, and NAND (not AND);
many combinations of these are possible as well.
Logic gates operate via hardware known as a
switch - in particular, a digital switch. In the days of room-size computers,
the switches were actually physical switches, but today nothing moves except
the current itself. The most common type of switch in today's computers is a
transistor known as a MOSFET (metal-oxide semiconductor field-effect
transistor).