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CompTIA A+ Certification All-in-One Exam Guide

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00000000000000001000

Hey, wouldn’t this be a great way to represent each line of RAM on the

address bus? The CPU identifies the first byte of RAM on the address bus

with 00000000000000000000. The CPU identifies the last RAM row with

11111111111111111111. When the CPU turns off all the address bus wires,

it wants the first line of RAM; when it turns on all the wires, it wants the

1,048,576th line of RAM. Obviously, the address bus also addresses all the

rows of RAM in between. So, by lighting up different patterns of ones and

zeros on the address bus, the CPU can access any row of RAM it needs.

NOTE Bits and bytes are abbreviated differently. Bits get a lowercase b,

whereas bytes get a capital B. So for example, 4 Kb is 4 kilobits, but 4 KB is

4 kilobytes. The big-B little-b standard applies all the way up the food chain,

so 2 Mb = 2 megabits; 2 MB = 2 megabytes; 4 Gb = 4 gigabits; 4 GB = 4

gigabytes; and so on.

1001

Modern CPUs

CPU manufacturers have achieved stunning progress with microprocessors

since the days of the Intel 8088, and the rate of change doesn’t show any

signs of slowing. At the core, though, today’s CPUs function similarly to the

processors of your forefathers. The arithmetic logic unit (ALU)—that’s the

Man in the Box—still crunches numbers many millions of times per second.

CPUs rely on memory to feed them lines of programming as quickly as

possible.

This section brings the CPU into the present. We’ll first look at models

you can buy today, and then we’ll turn to essential improvements in

technology you should understand.

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