15.01.2024 Views

CompTIA A+ Certification All-in-One Exam Guide

  • No tags were found...

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

The CPU needs a way to address each line of this memory—a way for the

CPU to say to the memory, “Give me the next line of code” or “Give me line

6.” Addressing memory takes care of another problem: the memory must

store not only programs but also the result of the programs. If the CPU adds 2

+ 3 and gets 5, the memory needs to store that 5 in such a way that other

programs may later read that 5, or possibly even store that 5 on a hard drive.

By addressing each line of memory, other programs will know where to find

the data.

Memory and RAM

Memory must store not only programs, but also data. The CPU needs to be

able to read and write to this storage medium. Additionally, this system must

enable the CPU to jump to any line of stored code as easily as to any other

line of code. All of this must be done at or at least near the clock speed of the

CPU. Fortunately, this magical device has existed for many years: random

access memory (RAM). Chapter 4, “RAM,” develops the concept in detail, so

for now let’s look at RAM as an electronic spreadsheet, like one you can

generate in Microsoft Excel (see Figure 3-14). Each cell in this spreadsheet

can store only a one or a zero. Each cell is called a bit. Each row in the

spreadsheet is 8 bits across to match the EDB of the 8088. Each row of 8 bits

is called a byte. In PCs, RAM transfers and stores data to and from the CPU

in byte-sized chunks. RAM is therefore arranged in byte-sized rows. Here are

the terms used to talk about quantities of bits:

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!