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Hexadecimal Addresses

Addresses in PC systems are always referred to by their hexadecimal value because digital computers are built on components that only work with two logic levels—either On/Off, High/Low, or 1/0. This corresponds directly to the Base-2 or binary numbering system. In the binary system, each piece of information represents a binary digit, or bit.

The power of the digital computer lies in how it groups bits of information into words. The basic word length in PCs is the 8-bit word called a byte. Some computers can handle data as 16, 32, and 64-bit words. With the byte as the basic data unit, it is easier for humans to speak of computer numbers in the Base-16 or hexadecimal (hex) numbering system. In this system, groups of 4 bits can be represented directly by a single hex character (that is, 1001 base2 = 09 base16). For human representation, the values in the numbering system run from 0 to 9 and then from A through F, as illustrated in Table 3.5.

Table 3.5 Decimal, Binary, and Hexadecimal Numbers

Decimal (10)

Binary (2)

Hex (16)

0

0000

0

1

0001

1

2

0010

2

3

0011

3

4

0100

4

5

0101

5

6

0110

6

7

0111

7

8

1000

8

9

1001

9

10

1010

A

11

1011

B

12

1100

C

13

1101

D

14

1110

E

15

11111

F

16

0000

10


Hands-On Activity For hands-on experience with this concept, refer to Lab Procedure #6, "PC Check," located on the CD that accompanies this book.

Although this might seem a little inconvenient for those of you not familiar with binary and hexadecimal systems, it is much easier to convey the number 3F8h to someone than it is 001111111000. The real difficulty of reconciling a hexadecimal value comes when you try to convert binary or hexadecimal values to the decimal (base 10) number system you are familiar with.

Reference Shelf For more information, refer to the Electronic Reference Shelf, "Bits, Bytes, and Computer Words," located on the CD that accompanies this book.

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