Editing 64-bit computing (section)

== Architectural implications ==
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Processor registers are typically divided into several groups: ''integer'', ''floating-point'', ''[[single instruction, multiple data]]'' (SIMD), ''control'', and often special registers for address arithmetic which may have various uses and names such as ''address'', ''index'', or ''base registers''. However, in modern designs, these functions are often performed by more general purpose ''integer'' registers. In most processors, only integer or address-registers can be used to address data in memory; the other types of registers cannot. The size of these registers therefore normally limits the amount of directly addressable memory, even if there are registers, such as floating-point registers, that are wider.

Most high performance 32-bit and 64-bit processors (some notable exceptions are older or embedded [[ARM architecture]] (ARM) and 32-bit [[MIPS architecture]] (MIPS) CPUs) have integrated floating point hardware, which is often, but not always, based on 64-bit units of data. For example, although the [[x86]]/[[x87]] architecture has instructions able to load and store 64-bit (and 32-bit) floating-point values in memory, the internal floating-point data and register format is 80 bits wide, while the general-purpose registers are 32 bits wide. In contrast, the 64-bit [[DEC Alpha|Alpha]] family uses a 64-bit floating-point data and register format, and 64-bit integer registers.