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CompTIA A+ Certification All-in-One Exam Guide

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Figure 3-6 The four general-purpose registers

Registers provide the Man in the Box with a workplace for the problems

you give him. All CPUs contain a large number of registers, but for the

moment let’s concentrate on the four most common ones: the generalpurpose

registers. Intel named them AX, BX, CX, and DX.

NOTE The 8088 was the first CPU to use the four AX–DX generalpurpose

registers, and they still exist in even the latest CPUs. (But they have

a lot more light bulbs!) In 32-bit processors, the registers add an E for

extended, so EAX, EBX, and so on. The 64-bit registers get an R (I don’t

know why), thus RAX, RBX, and so on.

Great! We’re just about ready to put the Man in the Box to work, but

before you close the lid on the box, you must give the Man one more tool.

Remember the codebook I mentioned earlier? Let’s make one to enable us to

communicate with him. Figure 3-7 shows the codebook we’ll use. We’ll give

one copy to him and make a second for us.

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