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CompTIA A+ Certification All-in-One Exam Guide

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Figure 3-15 Typical RAM

The CPU accesses any one row of RAM as easily and as fast as any other

row, which explains the “random access” part of RAM. Not only is RAM

randomly accessible, it’s also fast. By storing programs on RAM, the CPU

can access and run them very quickly. RAM also stores any data that the

CPU actively uses.

Computers use dynamic RAM (DRAM) for the main system memory.

DRAM needs both a constant electrical charge and a periodic refresh of the

circuits; otherwise, it loses data—that’s what makes it dynamic rather than

static in content. The refresh can cause some delays, because the CPU has to

wait for the refresh to happen, but modern CPU manufacturers have clever

ways to get by this issue, as you’ll see when you read about modern

processor technology later in this chapter.

Don’t confuse RAM with mass storage devices such as hard drives and

flash drives. You use hard drives and flash drives to store programs and data

permanently. Chapters 8 through 10 discuss permanent storage in intimate

detail.

Address Bus

So far, the entire PC consists of only a CPU and RAM. But the CPU and the

RAM need some connection so they can talk to each other. To do so, extend

the external data bus from the CPU so it can talk to the RAM (see Figure 3-

16).

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