Chapter 3. How Computers Measure and Transfer Data

In this chapter

• Measurement: Bits, Bytes, and Beyond

• Numbering Systems Used in Computers

• Serial Versus Parallel Information Transfer

How do computers measure information? By the byte. It's the basic unit of measurement for all parts of the computer that involve the storage or management of information (RAM, storage, ROM). Here are a few examples:

• Software stored on a floppy or hard disk occupies a finite number of bytes.

• RAM is measured in megabytes (1MB = 1,000,000 bytes).

• Drive capacity is measured in gigabytes (1GB = 1,000,000,000 bytes).

Understanding bytes and the other measurements derived from bytes is essential to choosing the correct sizes for RAM configurations, storage media, and much more. Some of the A+ Certification test questions typically deal with RAM and hard disk size measurements, as will your day-to-day work.

The CD included with this book contains important Study Lab material for this chapter, as well as Chapters 2 “22 in this book. The Study Lab for each chapter contains terms to study, exercises, and practice tests ”all in printable PDF format (Adobe Acrobat Reader is included on the CD, too). These Study Lab materials will help you gear up for the A+ Exam. Also, the CD includes an industry-leading test engine from PrepLogic, which simulates the actual A+ test so that you can be sure that you're ready when test day arrives. Don't let the A+ test intimidate you. If you've read the chapters, worked through the Study Lab, and passed the practice tests from PrepLogic, you should be well prepared to ace the test!

Also, you'll notice that some words throughout each chapter are in bold format. These are study terms that are defined in the Study Lab. Be sure to consult the Study Lab when you are finished with this chapter to test what you've learned.

So, what's a byte? If you are storing text-only information in the computer, each character of that text (including spaces and punctuation marks) equals a byte. Thus, to calculate the number of bytes in the following sentence , count the letters , numbers , spaces, and punctuation marks:

 "This book is written by Mark Edward Soper." 12345678901234567890123456789012345678901234                                               10          20       30        40 

From this scale, you can see that the sentence uses 44 bytes. You can prove this to yourself by starting up Windows Notepad (or using MS-DOS's EDIT) and entering the text just as you see it printed here. Save the text as EXAMPLE.TXT and view the directory information (MS-DOS) or the File properties. You'll see that the text is exactly 44 bytes.

Do most computer programs store just the text when you write something? To find out, start up a word-processing program, such as Windows WordPad or Microsoft Word. Enter the same sentence again, and save it as EXAMPLE.If you use WordPad, save the file as a Rich Text Format (.RTF) file and as a Microsoft Word (.DOC) file. Depending upon the exact version of WordPad or Microsoft Word you use, the file takes up much more space. For example, WordPad for Windows XP saves text as an RTF file, using 243 bytes to store the file. The same sentence takes 19,968 bytes when saved as a .DOC file by Microsoft Word XP!

What happened ? The next section explains this apparent oddity.