An operating system has to work closely with the hardware system that acts as its foundations. The operating system needs certain services that can only be provided by the hardware. In order to fully understand the Linux operating system, you need to understand the basics of the underlying hardware. This chapter gives a brief introduction to that hardware: the modern PC.
When the ``Popular Electronics'' magazine for January 1975 showing the Altair 8080 on its front cover, a revolution started. The Altair 8080, named after the destination of an early Star Trek episode, could be assembled by home electronics enthusiasts for a mere $397. With its Intel 8080 processor and 256 bytes of memory but no screen or keyboard it was puny by today's standards. Its inventor, Ed Roberts, coined the term ``personal computer'' to describe his new invention but the term PC is now used to refer to almost any computer that you can pick up without needing help. By this definition, even some of the very powerful Alpha AXP systems are PCs. Enthusiastic hackers saw the Altair's potential and start to write software and build hardware for it. To these early pioneers it represented freedom; the freedom from huge batch processing mainframe systems run and guarded by an elite priesthood. Overnight fortunes were made by college dropouts fascinated by this new phenominon, a computer that you could have at home on your kitchen table. A lot of hardware appeared, all different to some degree and software hackers were happy to write software for these new machines. Paradoxically it was IBM who firmly cast the mould of the modern PC by announcing the IBM PC in 1981 and shipping it to customers early in 1982. With its Intel 8088 processor, 64K of memory (expandable to 256K), two floppy disks and an 80 character by 25 lines Colour Graphics Adapter (CGA) it was not very powerful by today's standards but it sold well. It was followed, in 1983, by the IBM PC-XT which had the luxury of a 10Mbyte hard drive. It was not long before IBM PC clones were being produced by a host of companies such as Compaq and the architecture of the PC became a defacto standard. This standard helped a multitude of hardware companies to compete together in a growing market which, happily for consumers, kept prices low. Many of the system architectural features of these early PCs have carried over into the modern PC. For example, even the most powerful Intel Pentium Pro based system starts running in the Intel 8086's addressing mode. When Linus Torvalds started writing what was to become Linux he picked the most plentiful and reasonably priced hardware, an Intel 80386 PC.
Figure: A typical PC motherboard.
Looking at a PC from the outside, the most obvious components are a
system box, a keyboard, a mouse and a video monitor. On the front of
the system box are some buttons, a little display showing some numbers and a
floppy drive. Most systems these days have a CD ROM and if you feel that
you have to protect your data, then there will also be a tape drive for
backups. These devices are collectively known as the peripherals.
Whilst the CPU is in overall control of the system, it is not the only
intelligent device. All of the peripheral controllers, for example the IDE
controller, have some level of intelligence.
Inside the PC (Figure 
) you will see a motherboard
containing the CPU or microprocessor, the memory and a number of slots
for the ISA or PCI peripheral controllers.
Some of the controllers, for example the IDE disk controller may be built
directly onto the system board.