Intel ARCHITECTURE IA-32 User Manual download pdf (Page 43)

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Vol. 3A 1-7

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1.3.4 Hexadecimal and Binary Numbers

Base 16 (hexadecimal) numbers are represented by a string of hexadecimal digits followed by

the character H (for example, F82EH). A hexadecimal digit is a character from the following

set: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F.

Base 2 (binary) numbers are represented by a string of 1s and 0s, sometimes followed by the

character B (for example, 1010B). The “B” designation is only used in situations where confu-

sion as to the type of number might arise.

1.3.5 Segmented Addressing

The processor uses byte addressing. This means memory is organized and accessed as a

sequence of bytes. Whether one or more bytes are being accessed, a byte address is used to

locate the byte or bytes memory. The range of memory that can be addressed is called an

address space.

The processor also supports segmented addressing. This is a form of addressing where a

program may have many independent address spaces, called segments. For example, a program

can keep its code (instructions) and stack in separate segments. Code addresses would always

refer to the code space, and stack addresses would always refer to the stack space. The following

notation is used to specify a byte address within a segment:

Segment-register:Byte-address

For example, the following segment address identifies the byte at address FF79H in the segment

pointed by the DS register:

DS:FF79H

The following segment address identifies an instruction address in the code segment. The CS

CS:EIP

1.3.6 Syntax for CPUID, CR, and MSR Values

Obtain feature flags, status, and system information by using the CPUID instruction, by

checking control register bits, and by reading model-specific registers. We are moving toward a

single syntax to represent this type of information. See Figure 1-2.

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