Intel Architecture Software Developers Manual

Short Description
The Intel Architecture Software Developer’s Manual, Volume 2: Instruction Set Reference (Order Number 243191) is part of a three-volume set that describes the architecture and programming environment of all Intel Architecture processors. The other two volumes in this set are:
• The Intel Architecture Software Developer’s Manual, Volume 1: Basic Architecture (Order Number 243190).
• The Intel Architecture Software Developer’s Manual, Volume 3: System Programing Guide (Order Number 243192).
The Intel Architecture Software Developer’s Manual, Volume 1, describes the basic architecture and programming environment of an Intel Architecture processor; the Intel Architecture Software Developer’s Manual, Volume 2, describes the instructions set of the processor and the opcode structure. These two volumes are aimed at application programmers who are writing programs to run under existing operating systems or executives. The Intel Architecture Software Developer’s Manual, Volume 3, describes the operating-system support environment of an Intel Architecture processor, including memory management, protection, task management, interrupt and exception handling, and system management mode. It also provides Intel Architecture processor compatibility information. This volume is aimed at operating-system and BIOS designers and programmers.

Website: webster.cs.ucr.edu | Filesize: 3989kb
No of Page(s): 566

Content
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1.4.1. Bit and Byte Order
In illustrations of data structures in memory, smaller addresses appear toward the bottom of the figure; addresses increase toward the top. Bit positions are numbered from right to left. The numerical value of a set bit is equal to two raised to the power of the bit position. Intel Architecture processors is a “little endian” machines; this means the bytes of a word are numbered starting from the least significant byte. Figure 1-1 illustrates these conventions.
1.4.2. Reserved Bits and Software Compatibility
In many register and memory layout descriptions, certain bits are marked as reserved. When bits are marked as reserved, it is essential for compatibility with future processors that software treat these bits as having a future, though unknown, effect. The behavior of reserved bits should be regarded as not only undefined, but unpredictable. Software should follow these guidelines in dealing with reserved bits:
• Do not depend on the states of any reserved bits when testing the values of registers which contain such bits. Mask out the reserved bits before testing.
• Do not depend on the states of any reserved bits when storing to memory or to a register.
• Do not depend on the ability to retain information written into any reserved bits.
• When loading a register, always load the reserved bits with the values indicated in the documentation, if any, or reload them with values previously read from the same register.
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