ICDL Exam Cram 2

Now that you have the broad overview, let's focus a bit more on the computer's hardware. In this section, you cover the basic hardware knowledge that you should bring to your job and to the exam.

Central Processing Unit

The Central Processing Unit (CPU) is the brain of your computer. It performs several critical functions that you need to be familiar with.

Functions of the CPU

Although we often speak of the CPU as a single thing, in reality it's a very complex piece of electronics with many subcomponents. The CPU performs a number of different functions, including the following:

• Performing calculations When there are numbers to add or other calculations to perform, it happens in the CPU.

• Controlling logic Often your computer makes choices: which color to display, what calculations to perform, and so on. The logic of these choices is embodied in the CPU.

• Immediate access memory The CPU contains a small amount of fast memory to store intermediate results that it will need immediately.

• Coordinating other functions The CPU sends instructions to other components , such as the video card and the hard drive, telling them what to do.

The speed of the CPU is one of the most important factors in determining the overall performance of your computer. Speed is measured in megahertz (MHz); one MHz represents one million operations per second. A thousand MHz equals one gigahertz (GHz). In 2004, an older desktop computer that is still usable might have a CPU speed of about 500MHz. The newest and fastest CPUs have speeds of about 3GHz.

Memory

After the CPU, the second most critical part of the computer is the memory. Not all computers contain the same size or type of memory, and you need to know the differences when evaluating a computer's capabilities.

Types of Memory

Computer memory comes in two types : RAM and ROM .

RAM is the type of computer memory that people are usually talking about when referring to a computer's memory. When you run an application, the computer code that makes up that application and the results of your work are temporarily stored in RAM. RAM is comparatively inexpensive and can be reused many times by your computer; each part of the memory can be written to or read from repeatedly. RAM is also volatile . That is, anything stored only in RAM is lost when you turn off the computer.

ROM is a smaller area of memory that holds critical applications that run the computer itself. Information stored in ROM is there permanently, even when the computer is off. Most computers use ROM to hold the basic programs that make the computer and its display start up and become ready to hold other information.

Memory Size

The simplest unit of memory is the bit . A single bit is equal to either a numerical 1 or 0 at any given time. Each bit of memory is like a tiny switch that the computer can turn on or off: on equals 1 and off equals 0. This system is called the binary system of counting.

Modern computers contain many bits of memory, referred to in increasingly large units:

• A byte is 8 bits.

• A kilobyte (KB) is 1,024 bytes. Computers use binary arithmetic, which makes 1,024 a "round" number in computing terms.

• A megabyte (MB) is 1,024KB, or roughly 1 million bytes.

• A gigabyte (GB) is 1,024MB, or roughly 1 billion bytes.

• A terabyte (TB) is 1,024GB, or roughly 1 trillion bytes.

A modern personal computer will usually have between 128MB and 2GB of RAM. How much will this hold? Well, you can think of it in terms of the amount of text that you can store in each chunk of memory:

• A byte will hold a single character of the alphabet; each letter is represented by a particular code of 1s and 0s. (For example, the letter "A" is usually stored as 01000001 in "computer language.")

• A page of text will take about 5KB to store.

• This entire book takes up about 5MB of RAM.

• A GB of text would come to about 2,000 books, a good- sized personal library.

• The Library of Congress holds nearly 25 million books. That's about 12.5TB of text.

Of course, not all the information stored on your computer is in the form of text. Programs, graphics, sounds, movies, drawings, and other forms of information all take up RAM when they're current in your computer. A typical application might occupy anywhere from 100KB to 100MB of RAM while it's running.

Input Devices

Input devices allow you to send information to your computer. You need to know the major classes of input devices to pass the exam.

Identifying Input Devices

An input device is any piece of hardware that you can use to enter information (that is, send information to the computer). Here's a list of some of the common input devices that you might encounter:

• A mouse is an input device designed to be grasped with one hand and slid around on the desk. The computer translates this movement into the movement of the cursor (arrow) on your screen. A mouse also has one or more buttons that you can press to send instructions to the computer.

• A keyboard is an input device that includes the standard typewriter keys and other keys such as function keys, arrow keys, and a numeric keypad. The keyboard is the device most often used to input text to a computer program.

• A trackball resembles an upside-down mouse. The trackball stays in one spot on your desk, with a ball facing upwards. Moving the ball moves the cursor onscreen. Like a mouse, a trackball has one or more buttons that you can press. Figure 2.2 shows a mouse and a trackball.

  Figure 2.2. A mouse and a trackball.

• A scanner is an input device that can convert a printed sheet of paper (or other flat object) into a file that the computer can store. Some scanners are standalone devices, whereas others are built into printers or other multipurpose devices.

• A touchpad is a small rectangular area, usually built into a laptop computer, where you can drag your finger to move the cursor onscreen.

• A light pen looks a bit like a penlight with a cord coming out of the end. You can indicate a spot on your computer monitor by pointing at it with the light pen and clicking a button.

• A joystick is an input device somewhat similar to the control stick of an airplane. Joysticks are most frequently used as input devices for computer games , but they do have some use in business settings as well.

• A digital camera allows you to take pictures without film by storing them in memory inside the camera. Later, you can use a special cable or other adapter to load these pictures into your computer.

• A microphone lets you use speech as an input to the computer. Depending on the software that you have installed, you can either store the speech to be played back later or use it to issue commands that the computer will understand.

Output Devices

Output devices let your computer communicate information back to you. You should know about some of the major categories of output devices.

Identifying Output Devices

An output device is any piece of hardware that the computer can use to convey information back to you. Here are some common output devices that you might run across:

• A monitor is a video display device sometimes informally called the computer's screen. It is the main place where you will receive information from the computer.

• A printer is a device suited to produce printed output on paper. There are a wide variety of printers; they differ in their speed, the size of the paper they can print on, and the process that they use for printing. Printers are useful when you need a temporary or permanent record of some information away from your computer.

• A plotter is a device that moves one or more pens over a piece of paper to create a drawing. Plotters are typically used for output such as architectural drawings and mechanical designs.

• Speakers allow your computer to communicate with you using sound. The sound can be anything from a warning beep when something goes wrong to synthetic voices that can read the information displayed on the monitor.

Input/Output Devices

Some peripheral devices do double duty as both input devices and output devices.

Two Devices in One

The most common example of an input/output device (that is, a peripheral that can act as both an input device and an output device) is a touchscreen. A touchscreen looks like a monitor. However, the surface of the touchscreen is sensitive to touch, either with a finger or with a specialized stylus. Thus, a touchscreen can act as both a monitor and a cursor-control device similar to a touchpad at the same time.

Storage Devices

Input and output devices are concerned with moving information in and out of the computer. But where does the information go when it's in the computer? The answer is that it ends up in a storage device.

Comparing Storage Devices

Personal computers use a wide array of storage devices. Also, the types of storage devices are constantly changing. Here are some of the storage devices that you might encounter in the workplace:

• A diskette is a small removable storage device, sometimes called a "floppy disk."

• A Zip disk is a proprietary device about the size of a diskette but with a hard plastic shell and a much higher storage capacity.

• A data cartridge holds magnetic tape and is designed to use with a special tape drive as a way to back up large amounts of data.

• A CD-ROM is a plastic disk, similar to a music CD.

• Internal and external hard drives are permanently sealed magnetic storage devices that are capable of storing large amounts of data. Internal drives are inside the housing of the computer, but there are hard drives that can connect to the computer outside the computer housing.

Table 2.2 will help you compare these storage devices.

Table 2.2. Comparing Storage Devices

Most of these storage devices are read/write devices. That is, you can both read the information that's written on them and write new information to them. The CD-ROM is an exception, being a read-only device. Information written to a CD-ROM cannot be deleted.

Formatting Disks

Most storage devices (including diskettes, Zip disks, and hard disks) must be formatted before they can be used. The formatting process checks the disk to make sure that it is in good condition and lays down guidelines that tell the disk drive where it can write information. These guidelines divide the disk into tracks and sectors , as shown in Figure 2.3. The operating system can put a fixed amount of data into each area of the disk that formatting creates.