ne or zero, on or off, positive or negative, presence of voltage or absence of voltage, pres- ence of light or absence of light. There are two possible values for any given situation, and this type of system is called binary. The word means a system that comprises two distinct components or values. Computers operate using base two arithmetic, whereas humans use base ten. Let me take you back to second grade. When we count, we arrange our numbers in columns that have values based on multiples of the number ten, as shown in Figure 2-5. Here we see the number six thousand, seven hundred eighty-three, written using the decimal numbering scheme. We easily understand the number as it is written because we are taught to count in base ten from an early age. Computers, however, don't speak in base ten. Instead, they speak in base two. Instead of having columns that are multiples of ten, they use columns that are multiples of two, as shown in Figure 2-6. In base ten, the columns are (reading from the right): Hundreds Thousands Ten thousands Hundred thousands Millions Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Protocols Thousands Figure 2-5 Base ten numbering scheme 6,783 Hundreds In base two, the columns are Fours Eights Sixteens Thirty-twos Sixty-fours One hundred twenty-eights Two hundred fifty-sixes Five hundred twelves One thousand twenty-fours Figure 2-6 hundred Base two twelves hundred numbering Two thousand twenty- Thirty- forty-eights eights Eights scheme 1101001111111 One Two hundred Sixty- Sixteens Fours thousand fifty- fours twenty-fours sixes Four thousand ninety-sixes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Chapter 2 So our number, 6,