A computer is a complex electronic machine, but its operations can
be understood sufficiently in terms of a few interconnected components:
The processor is further divided into two smaller components
In the picture note that the components are connected through a set of
wires called the bus.
A computer model showing the processor, memory, and I/O devices.
The operations of any processor are as follows ad infinitum
This is called the fetch/execute cycle. Note that the
processor is so much faster than the I/O devices, that I/O
doesn't appear prominently here. A modern processor is able to execute
millions of instructions while waiting for an I/O device, even a fast
device like the disk or the network.
The main point here is that the computer doesn't know how to do
anything "automatically": there's always some program code (set of
instructions) telling it how to do something.
The input/output unit is connected with the usual peripherals such as
keyboard, mouse, the various "drives" (such as hard drives, floppy drives,
zip drives, DVD drives, CDROM drives, etc), monitors, printers etc. So,
the components and operations of a computer are remarkably
simple. Complication enters only for performance reasons, but any computer
that you are likely to see these days contains the above components.
Looking at the picture above, you see a big yellow box
labeled Memory, but you'll also see, if you look closely, hard
drive attached to the bus. What's the difference? Does it matter?
Yes, it does. The memory we describe there is super-fast memory chips
that are right on the circuit board, just a few inches from the
processor, what is sometimes
or Random Access Memory. The most important properties of RAM are
If you've ever lost a document you were working on using your computer
because the power went out or your battery ran out, that's because the
stuff you were working on was in volatile memory. The files
that are saved on the hard drive weren't lost.
drive of your computer is (usually) a spinning disk with magnetic
coating that stores the zeros and ones of your files as a pattern of
magnetization. The exact representation isn't important, but two
properties of hard drives are crucial:
There are other kinds of drives, such as solid-state drives, but the
same properties appear. These properties mean that your computer mostly
works by copying information (both programs and data, such as your
files) from long-term storage on the hard drive into fast memory in the
RAM, and that's where it stays while the computer is running. But you
should save your stuff in RAM to hard disk on occasion, in order to
avoid losing your work should someone trip on your power cord and pull
the plug, or your battery unexpectedly die.
Finally, the most recent technology (invented in the past 15 years) is
the USB flash drive
, which has become the ubiquitous choice for
transferring information between devices.