computer science

CHAPTER 1 — Introduction to Computer Systems

Chapter Topics:

Hardware and Software
Components of a Computer System
Networks
World-Wide Web

A. Hardware and Software:
the word hardware is used for physical devices such as TV sets, DVD players and computers. The word software is used for the information used with such devices: movies, music, novels, computer programs, and data.

B. Components of a Computer System:
A computer system consists of both hardware and software components.

The hardware components of a computer system are the electronic and mechanical parts.
The software components of a computer system are the data and the computer programs.

The major hardware components of a computer system are:

Processor
Main memory
Secondary memory
Input devices
Output devices

Hardware Components:
A bus is a group of wires on the main circuit board of the computer. It is a pathway for data flowing between components. Most devices are connected to the bus through a controller which coordinates the activities of the device with the bus.

The processor is an electronic device about a one inch square, covered in plastic. Inside the square is an even smaller square of silicon containing millions of tiny electrical parts.

Memory

This memory is of two fundamental types:

Main memory:

closely connected to the processor.
stored data are quickly and easily changed.
holds the programs and data that the processor is actively working with.
interacts with the processor millions of times per second.
needs constant electric power to keep its information.

Secondary memory:

connected to main memory through the bus and a controller.
stored data are easily changed, but changes are slow compared to main memory.
used for long-term storage of programs and data.
before data and programs can be used, they must be copied from secondary memory into main memory.
does not need electric power to keep its information.

Main Memory:

Main memory is where programs and data are kept when the processor is actively using them. When programs and data become active, they are copied from secondary memory into main memory where the processor can interact with them.

Secondary Memory:

Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks.

The hard disk has enormous storage capacity compared to main memory.
The hard disk is usually contained inside the case of a computer.
The hard disk is used for long-term storage of programs and data.
Data and programs on the hard disk are organized into files.
A file is a section of the disk that has a name.

The reason for having two types of storage is this contrast:

Primary memory:
Fast
Expensive
Low capacity
Works directly with the processor

Secondary memory:
Slow
Cheap
Large capacity
Not connected directly to the processor

Input Device:
Input and output devices allow the computer system to interact with the outside world by moving data into and out of the system. An input device is used to bring data into the system.

Some input devices are:

Keyboard
Mouse
Microphone
Bar code reader
Graphics tablet

Output Device:
An output device is used to send data out of the system.

Some output devices are:

Monitor
Printer
Speaker