The personal computer
The type of machine that we now describe as a PC means one that is modelled on the IBM PC (Personal Computer) type of machine that ﬁ rst appeared in 1981. The reason that this type of machine has become dominant is the simple one of continuity: programs that will work on the original IBM PC machine will work on later versions and some (but certainly not all) will still work even on today’s much more developed machines. By maintaining compatibility, the designers have ensured that when you change computer, keeping to a PC type of machine, you do not immediately need to change software (programs). Since the value of your software is much greater than the value of the hardware (the computer itself), this has ensured that the PC type of machine has become dominant in business and other serious applications. Other types of computer are not compatible with the PC or with each other, and have less choice of software and more expensive components.