MEMORY ALIGNMENT

8/9/97

Memory Alignment: The Intel 80x8x CPUs, like many other CPUs, use variables of different sizes. Bytes (8 bits); 2 byte words; and 4 byte double words for example. Many CPUs, such as the Motorola 68000 require that two byte entities be at even addresses and 4 byte entities be at addresses divisible by 4 This is known as alignment. Alignment substantially eases the design of hardware interfaces. The 80x8x does not require byte, word double word or paragraph (16 bytes) alignment. But it does introduce some timing penalties for operating on non-aligned data.

Variation in timing between aligned and non-aligned data can be a problem when benchmarking using tight program loops on single data blocks.

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