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Chapter 5
System Software
System Software
• There is software stored in the ROM circuits contain
important system routine on every motherboard.
• When you switch on your PC receives instructions
which are loaded into the CPU, and the CPU starts by
executing the system software which is stored on the
motherboard.
• The startup programs are stored in ROM circuits
which contain data, and can only be read.
• BIOS is important system software, only after these
programs have been loaded and executed, then the
operating system can be loaded from the hard disk.
This is called the boot process.
BIOS ROM (Basic Input output System
Read Only Memory)
• contain software (program and instructions), which are
specific for that motherboard. It will remain with the
PC throughout its life.
• holds the start-up instructions. In fact there are several
different programs inside the start-up instructions. It can
be differentiate by:
– POST (Power On Self Test)
– The Setup program, which connect with the *CMOS instructions
– BIOS program, which connect with the various hardware
peripherals
– The Boot instructions, which call the operating system (DOS,
OS/2, or Windows)
Start-Up Instruction in the BIOS
POST routine
The SETUP program
The BIOS programs
ROM Chip
The BOOT instructions
POST
• (POST) Power On Self Test is the first instruction
executed during start-up. It checks the PC
components and ensures that everything works.
• It checks and executes in this order:
– Information about the graphics adapter.
– Information about the BIOS (name, version).
– Information about the RAM (size and speed)
• If POST detects errors in the system, it will write
error messages on the screen. If the monitor is not
ready, or if the error is in the video card, it will give a
pattern of beeps.
Setup program
• Checks the various hardwares, configure in the
CMOS, and generally “bringing the machine to life”.
• Installs the other system devices:
– such as floppy disk and ATA drives,
– locates the “logical devices” (eg. COM, LPT, etc.).
– The PCI bus is also scanned for devices.
BIOS program
• It initializing routine set up the BIOS functions
(Basic Input/Output Systems).
• It places starting values in the system’s various
programmable devices.
• These intelligent devices regulate the operation of
different portions of the computer’s hardware e.g.
data transfer control.
Boot instructions
• The boot instruction (bootstrap loader) is the last part
of the BIOS. It will looks in the CMOS storage to find the
chosen boot device.
• It is a tiny program, to find the Boot Record (BR) which
is located in the first sector on a hard disk or a floppy
disk.
• It reads the boot-strap of the Boot Record which points
to the location of the startup files of the Operating
System.
• It hands over the control to the bootstrap routine found
on the disk of the OS and continues loading the
operating system from the hard disk,
Operating System
• Operating systems are programs designed to
control the operation of a computer system.
• To make the complexity of the PC as invisible as
possible to the user.
• Acts as an intermediary between the software
applications and the hardware they run on.
• It accepts commands from the computer user
and carries them out to perform some desired
operation.
Disk Operating System (DOS)
• is a collection of programs used to control overall computer
operation.
• work in the background.
• is responsible for finding and organizing data, and applications
on the disk.
• It principally consists of only 4 parts:
– A boot record, which activates the operating system.
– IO.SYS file, which interfaced ROM BIOS with installation of device
drivers.
– MSDOS.SYS file, which handling the file system and program
execution.
– COMMAND.COM file, which provides the command line, the text
based user interface.
Other Operating System
• A Graphical User Interface (GUI) is another form of
operating environment.
• The most widely used GUI is Microsoft Window OS,
Apple OS and Linux.
• GUIs use a graphical display to represent procedures
and programs that can be executed by the computer.
• It uses small pictures, called Icons, to represent
different programs.
• The advantage of using a GUI is that the user does not
have to remember complicated commands to execute
a program.