Hardware Reference
In-Depth Information
Figure 1.1
Elements of a microcomputer system
connected together by a bus system along which data, address, and control
signals are passed, as shown in Figure 1.1.
The CPU is the microprocessor itself (e.g. a x86 or Pentium device), whilst
the read/write and read-only memory are implemented using a number of semi-
conductor memory devices (RAM and ROM, respectively).The semiconductor
ROM provides non-volatile storage for part of the operating system code (the
code remains intact when the power supply is disconnected, whereas the semi-
conductor RAM provides storage for the remainder of the operating system
code, applications programs, and transient data. It is important to note that this
memory is volatile, and any program or data stored within it will be lost when
the power supply is disconnected.
The operating system is a collection of programs and software utilities that
provide an environment in which applications software can easily interact with
system hardware. The operating system also provides the user with a means of
carrying out general housekeeping tasks, such as disk formatting, disk copying,
etc. In order to provide a means of interaction with the user (via keyboard
entered commands and onscreen prompts and messages), the operating system
incorporates a shell program (e.g. the COMMAND.COM program provided
within MSDOS).
Part of the semiconductor RAM is reserved for operating system use and
for storage of a graphic/text display (as appropriate). In order to optimize the
use of the available memory, most modern operating systems employ memory
management techniques which allocate memory to transient programs and then
release the memory when the program is terminated. A special type of pro-
gram (known as a 'terminate and stay resident' program) can, however, remain
resident in memory for immediate execution at some later stage (e.g. when
another application program is running).
I/O devices provide a means of connecting external hardware, such as key-
boards, displays, and disk controllers. I/O is usually handled by a number of
specialized VLSI devices, each dedicated to a particular I/O function (such as
disk control, graphics control, etc.). Such I/O devices are, in themselves, very
complex and are generally programmable (requiring software configuration
during system initialization).
