According to Intel's definition of a x86 16-bit Word, a Double Word refers a 32-bit entity, while IBM 360 and successors with 32-bit words have double words with 64-bit.
Integer and long
Even in x86-64, double words are still considered as default word size. x86 and and x86-64C-Compiler use double words as signed and unsigned integers, Java integers as well. Microsoft 64 bit compiler long is a 32-bit Double word as well, while with 64-bit GCC uses 64-bit Quad Words as longs.
Double Words stored in memory should be stored at byte addresses divisible by four. Otherwise at runtime it will cause a miss-alignment exception on some processors, or a huge penalty on others.
Table of Contents
According to Intel's definition of a x86 16-bit Word, a Double Word refers a 32-bit entity, while IBM 360 and successors with 32-bit words have double words with 64-bit.
Integer and long
Even in x86-64, double words are still considered as default word size. x86 and and x86-64 C-Compiler use double words as signed and unsigned integers, Java integers as well. Microsoft 64 bit compiler long is a 32-bit Double word as well, while with 64-bit GCC uses 64-bit Quad Words as longs.Ranges
Alignment
Double Words stored in memory should be stored at byte addresses divisible by four. Otherwise at runtime it will cause a miss-alignment exception on some processors, or a huge penalty on others.Endianness
Main article: Endianness.Litte-endian layout
The little-endian memory layout, as typical for Intel x86 cpus.For instance the double word integer 16909060 or 0x01020304:
Big-endian layout
The big-endian memory layout, as typical for Motorola cpus.For instance the double word integer 16909060 or 0x01020304:
See also
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