SF-Study Guide: Computer Components

Introduction

Hardware

As we learned in the Overview portion of the study guide, a computer system has two basic parts: hardware and software. The equipment associated with a computer system is the hardware. Computer hardware is responsible for performing four basic functions: input, processing, output, and storage. Let’s go back to the basic definition of a computer. A computer is an electronic device that is programmed to accept data (input), process it into useful information (output), and store it for future use (storage). The processing function is under the control of a set of instructions (software); we will explore this later.
The four primary components of a computer system are:

Input	Input devices send data and instructions to the central processing unit.
Output	Central processing unit executes computer instructions. Memory holds data and programs temporarily.
Processing	Output devices make processed data available to the user.
Secondary Storage	Secondary storage devices store data and programs permanently.

In order to function properly, a computer system must have all four types of hardware: input, processing, output, and storage.

In this example, the mouse and keyboard are the input devices and the monitor and speakers are output devices. The processor is contained inside the tower unit and the storage devices are the hard drive, CD-ROM drive and the diskette drive. Let’s explore each of the devices in detail.
Input devices accept data in a form that the computer can utilize. Also, the input devices send the data or instructions to the processing unit to be processed into useful information. There are many examples of input devices, but the most commonly used input devices are shown below:

The input device feeds data, raw unprocessed facts, to the processing unit. The role of the processing unit or central processing unit is to use a stored program to manipulate the input data into the information required. In looking at the computer system below, the Central Processing Unit, CPU, is not exactly visible. The CPU is found inside the tall, vertical unit, called a tower, located just to the right of the monitor.

The CPU is the brain of the computer. The CPU consists of electronic circuits that interpret and execute instructions; it communicates with the input, output, and storage devices. The CPU, with the help of memory, executes instructions in the repetition of machine cycles. A machine cycle consists of four steps:

1. The control unit fetches an instruction and data associated with it from memory.
2. The control unit decodes the instruction.
3. The arithmetic/logic unit executes the instruction.
4. The arithmetic/logic unit stores the result in memory.

The first two instructions are called instruction time, I-time. Steps 3 and 4 are called execution time, E-time. The speed of computer is measured in megahertz, MHz.
A MHz is a million machine cycles per second. A personal computer listed at 500 MHz has a processor capable of handling 500 million machine cycles per second. Another measure of speed is gigahertz (GHZ), a billion machine cycles per second. A third measure of speed is a megaflop, which stands for one million floating-point operations per second. It measures the ability of the computer to perform complex mathematical operations.
Memory, or primary storage, works with the CPU to hold instructions and data in order to be processed. Memory keeps the instructions and data for whatever programs you happen to be using at the moment. Memory is the first place data and instructions are placed after being input; processed information is placed in memory to be returned to an output device. It is very important to know that memory can hold data only temporarily because it requires a continuous flow of electrical current. If current is interrupted, data is lost. Memory is in the form of a semiconductor or silicon chip and is contained inside the computer.

There are two types of memory: ROM and RAM. ROM is read only memory. It contains programs and data that are permanently recorded when the computer is manufactured. It is read and used by the processor, but cannot be altered by the user. RAM is random access memory. The user can access data in RAM memory randomly. RAM can be erased or written over at will by the computer program or the computer user. The amount of RAM has increased dramatically in recent years.

Memory is measured in bytes. A byte is usually made up of 8 bits and represents one character—a letter, digit, or symbol. The number of bytes that can be held is a measure of the memory and storage capacity. Bytes are usually measured in groups of kilobytes, megabytes, gigabytes, and terabytes. The following chart defines each term.

Kilobyte	KB	Roughly 1,000 bytes
Megabyte	MB	Roughly 1,000,000 bytes
Gigabyte	GB	Roughly 1,000,000,000 bytes
Terabyte	TB	Roughly 1,000,000,000 bytes

Memory is usually measured in Megabytes; a typical personal computer will have 64MB or more. Storage is usually measured in Gigabytes.
Since we have said that memory is in the form of chips and must maintain a constant flow of electricity, there must be a more permanent form of storage that does not depend on a constant flow of electricity. That form of storage is called secondary or auxiliary storage. The benefits of secondary storage are large space capacity, reliability, convenience and economy.
Magnetic disk storage is a very popular type of secondary storage—the floppy disk drive is an external disk drive, while a hard disk drive is an internal disk drive. The floppy disk drive is usually a 3 ½" drive and uses a diskette made of flexible mylar and coated with iron oxide, a substance that can be magnetized. A diskette records data as magnetized spots on the tracks of its surface. A floppy disk can hold 1.44 MBs, or a ‘Zip’ drive can hold 100 MBs.
A hard disk, an internal disk, is a metal platter coated with magnetic oxide that can be magnetized to represent data. Hard disks come in a variety of sizes and can be assembled into a disk pack. Hard disks for personal computers are 3 ½" disks in sealed modules. A hard disk is capable of holding a great deal more than floppy disks. Hard disks for personal computers are measured in gigabytes. (Remember, a gigabyte is roughly a thousand megabytes or a thousand floppy disks.)
While the size or data capacity of a hard drive is very important, the speed of accessing that data is equally as important. Files on hard drives can be accessed significantly faster and more conveniently than floppy drives.

Hard Drive

The ever-demanding need for storage has required even better storage capacity than that of magnetic disks. Optical disk technology meets that need. Included in the list of this type of technology is the optical disk, the CD-ROM or DVD-ROM. The CD-ROM, compact disk read-only memory can hold up to 660 MBs per disk or the equivalent of more than 400 standard 3 ½" diskettes. The new storage technology that outpaces all others is called DVD-ROM, digital versatile disk. The DVD has a 4.7 GB capacity, which is about seven times that of the CD-ROM.
In order to protect the data on your hard drive, you should have a backup system. A backup system is way of storing data in more than one location. Magnetic tape is usually used for this purpose. Magnetic tape is an inexpensive type of storage; it looks like the tape used in audiocassettes.
Finally, the last component of a computer system is the output device. An output device displays the processed information to the user. The two most popular forms of output devices are the printer and the monitor. The monitor produces output that is temporary—the output is lost when it is rewritten or erased or when power is lost. Monitor output is called softcopy. The printer displays output in a permanent manner; it is called hardcopy. Other types of output devices include voice output and music output devices.

Software

As important as hardware devices may be, they are useless without the instructions that control them. These instructions used to control hardware and accomplish tasks are called software. Software falls into two broad categories— applications and systems software.
Applications software allows you to perform a particular task or solve a specific problem. A word processor is the most widely used example of applications software; it can be used to create a letter or memo or anything else you need to type. Other examples include games, spreadsheets, tax preparation programs, typing tutor, etc. Applications software can be purchased in stores and is called packaged or commercial software. In other words, it is prewritten. However, there may be situations that require a specific type of software that is not available. It would then be necessary to design and write a program; this software is called custom software. Most often, personal computers utilize packaged software.
When packaged software is purchased, it will come with written instructions for installation and use. These instructions are documentation. Packaged software can be purchased, or in some cases, it is available for no cost. Freeware is software considered to be in the public domain, and it may be used or altered without fee or restriction. Another form of somewhat free software is shareware. The author of shareware hopes you will make a voluntary contribution for using the product.
Task-oriented software is sometimes called productivity software, because it allows you to perform tasks that make you more productive. The major categories of productivity software are word processing, spreadsheet, database management, graphics, and communications. Most often these categories of software are bundled together and sold as a single package. This is called an office suite. A suite is designed to work together. This is very important because this allows you to share files. Another advantage in using suites is that the software looks similar and reduces your learning curve. Microsoft Office is the most popular office suite for the personal computer today. Two other important office suite products are Corel’s WordPerfect Office Suite and Sun’s Star Office Suite.

The most important applications software categories included in office suites are described in the table below:

Software Category	Function
Word Processor	Provides the tools for entering and revising text, adding graphical elements, formatting and printing documents.
Spreadsheets	Provides the tools for working with numbers and allows you to create and edit electronic spreadsheets in managing and analyzing information.
Database Management	Provides the tools for management of a collection of interrelated facts. Data can be stored, updated, manipulated, retrieved, and reported in a variety of ways.
Presentation Graphics	Provides the tools for creating graphics that represent data in a visual, easily understood format.
Communication Software	Provides the tools for connecting one computer with another to enable sending and receiving information and sharing files and resources.
Internet Browser	Provides access to the Internet through a service provider by using a graphical interface.

As important as applications software may be, it is not able to directly communicate with hardware devices. Another type of software is required operating systems software. Operating Systems software is the set of programs that lies between applications software and the hardware devices.
Think of the cross section of an onion. The inner core of the onion represents the hardware devices, and the applications software represents the outside layer. The middle layer is the operating systems software. The instructions must be passed from the outer layer through the middle layer before the reaching the inner layer.

The onion example

All computers, regardless of size, require the operating systems software. As soon as your personal computer is turned on, the operating systems software is loaded into RAM in order to use your computer devices and other software. A few short years ago, personal computers used an operating system call MS-DOS, Microsoft Disk Operating System. This was a command-driven program in which you needed to know command names and syntax. The need for a more user-friendly system brought about Microsoft Windows operating systems software. Icons or pictures, requiring no knowledge of spelling or syntax, drive Windows operating systems software. Windows is a GUI, graphical user interface. A GUI uses graphic symbols, icons, in its interface. Further, Windows allows you to multitask, which means that you may use more than one program at the same time. The newest version of Windows is Windows 2000.

Some notable features of the Windows 2000 are

• Internet/intranet browsing capabilities
• Support for state-of-the-art hardware
• Support for huge disk drives
• Wizards

In summary, the components of a computer include hardware and software that work together to perform the task necessary to transform raw data into useful information.