When this operation is used, which is calledanding, two bit values are combined
(compared) to produce a result. For example, if the two bit values are both 1s, the result is 1.
The value 1 represents true. Applying the two rules, two 1s make a 1. The logic is this and
that must be true. Trust me on this. However, if one of the bits contains a 0 (false), then
one truth and one false would result in a false. This is the basic logic used in electronic
logic circuits.OR Operations
The OR Boolean algebra operations have only one rule: if either of two values is a 1 (true),
then the result is a 1. The logic here is this or that can be true.Exclusive OR Operations
AnExclusiveOR(alsoknownasanXOR)operationrequiresone,andonlyone,ofthetwo
bit operands to be true, exclusive of the other bit’s value. So, in an XOR logical operation, if
oneandonlyonebitistrue(1),thenthepairresultsinatrue.Ifbothorneitherofthebitsis
true, the result is false (0). Exclusive OR operations are used to produce the complement
of a number.The Hexadecimal System
Another number system that is also used with the PC to express large numbers and
addresses: hexadecimal numbers.Hexadecimalmeans six and ten or a radix of 16. Hex, as
it is commonly called, uses 16 values to express its values—the decimal numbers 0
through 9 and the six letters A through F to represent the decimal values of 11–15.
Hexadecimal numbers use four bits, or a nybble, to store each of its digits. In its four
bits, a nybble can represent the decimal values 0 to 15 or the hexadecimal values 0 to F.
Because of its larger radix (16), hexadecimal is able to store each of the values 11 through 15
as a single character.
The number 101, which is one hundred and one in decimal and five in binary, is now
worth 257 in hexadecimal. This shows how well larger values are stored in hexadecimal.
AnotherexampleisthatthehexadecimalvalueABCDEFistheequivalentof11,259,375in
decimal. For more information on hexadecimal, see Chapter 2.Semiconductors
A microprocessor is constructed of layer upon layer of electronic circuits that are literally
carved out of silicon.Siliconis a very commonly found element in the world. In fact, after
oxygen, there is more silicon available than any other element, and you can find it easily
on the beach in rocks and sand. However, the silicon used for manufacturing integrated
circuits is found in white quartz.
Siliconistheprimarybuildingmaterialusedinmanufacturingtheelectronicintegrated
circuits (chips) that are used to construct the processor and ultimately the computer. It is
used in electronic circuits because it is an excellent semiconductor. Asemiconductoris aChapter 3: Microprocessors^45