A computer is an electronic device that stores and processes data. A computer includes both
. In general, hardware is the physical aspect of the computer that can be seen, and software is the invisible instructions that control the hardware and make it perform specific
A computer consists of the following major hardware components, as shown in Figure 1.1.
Central Processing Unit (CPU)
Memory (main memory)
Storage Devices (disks, CDs, tapes)
Input and Output Devices (
Communication Devices (modems and network interface cards (NICs) )
The components are connected through a subsystem called a bus that transfers data or power between the components.
central processing unit
is the brain of a computer. It retrieves instructions from memory and executes them. The CPU usually has two components: a
. The control unit controls and coordinates the actions of the other components. The arithmetic and logic unit
Today's CPU is built on a small silicon semiconductor chip with millions of
Computers use zeros and ones because digital devices have two stable states, referred to as
by convention. Data of various kinds, such as
The programmer need not be
A program and its data must be brought to memory before they can be executed. A memory byte is never empty, but its initial content may be meaningless to your program. The current content of a memory byte is lost whenever new information is placed in it.
Every byte has a unique address. The address is used to locate the byte for storing and retrieving data. Since the bytes can be accessed in any order, the memory is also referred to as
(random-access memory). Today's personal computers usually have at least 128 megabytes of RAM. A
(abbreviated MB) is about 1 million bytes. For a precise definition of megabyte,
Memory is volatile, because information is lost when the power is turned off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. The reason for this is that memory is much faster than storage devices. There are four main types of storage devices:
CD drives (CD-R, CD-RW, and DVD)
USB flash drives
Drives are devices for operating a medium, such as disks, CDs, and tapes.
There are two kinds of disks:
. Personal computers usually have a 3.5-inch floppy disk drive and a hard drive. A floppy disk has a fixed capacity of about 1.44 MB. Hard disk
CD stands for compact disc. There are two types of CD drives: CD-R and CD-RW. A
is for read-only permanent storage, and the
DVD stands for digital versatile disc. DVDs and CDs look alike. You can store data using a CD or DVD. A DVD can hold more information than a CD. A standard DVD storage is 4.7 GB in capacity.
Tapes are mainly used for backup of data and programs. Unlike disks and CDs, tapes store information sequentially. The computer must retrieve information in the order it was stored. Tapes are very slow. It would take one to two hours to back up a 1-gigabyte hard disk.
USB flash drives
are popular new devices for storing and transporting data. They are small ”about the
Input and output devices let the user communicate with the computer. The common input devices are keyboards and mice . The common output devices are monitors and printers .
A computer keyboard resembles a typewriter keyboard except that it has extra keys for certain special functions.
Function keys are located at the top of the keyboard with prefix F. Their use depends on the software.
A modifier key is special key (e.g., Shift, Alt, Ctrl) that modifies the normal action of another key when the two are pressed in combination.
The numeric keypad, located on the right-hand corner of the keyboard, is a separate set of number keys for quick input of numbers.
Arrow keys, located between the main keypad and the numeric keypad, are used to move the cursor up, down, left, and right.
The insert, delete, page up, and page down keys , located above the arrow keys, are used in word processing for performing insert, delete, page up, and page down.
A mouse is a pointing device. It is used to move an electronic pointer called a cursor around the screen or to click on an object on the screen to trigger it to respond.
The monitor displays information (text and graphics). The resolution and dot pitch determine the quality of the display.
The resolution specifies the number of pixels per square inch. Pixels (short for "picture elements") are tiny dots that form an image on the screen. A common resolution for a 17-inch screen, for example, is 1024 pixels wide and 768 pixels high. The resolution can be set manually. The higher the resolution, the sharper and clearer the image is.
The dot pitch is the amount of space between pixels. Typically, it has a range from 0.21 to 0.81 millimeters. The smaller the dot pitch, the better the display.
Computers can be networked through communication devices. Commonly used communication devices are the dialup
, and network interface card. A dialup modem uses a phone line and can transfer data at a speed up to 56,000 bps (bits per second). A DSL (digital subscriber line) also uses a phone line and can transfer data at a speed 20 times faster than a dialup modem. A cable modem uses the TV cable line