Re:Build your own Linux
by userbinator on Wednesday August 16, 2017 @11:07PM
(#15033503)
n-bit system has always been a bit of a vague term --- think of all the CPUs out there described as "8-bit" --- the 8080/8085/Z80 family, 6502, 8051, etc. None of them have an 8-bit address space, since otherwise they would only be able to address 256 bytes.
Even defining the address space is not trivial, with things like virtual vs. physical ("32-bit" x86 since the Pentium Pro actually has 36-bit physical addresses) and bankswitching (common on MCUs).
Likewise, data width is equally as complex: the Z80, commonly known as 8-bit, actually has operations on 16-bit "register pairs". 32-bit x86 with MMX has 64-bit registers, and with x87 has 80-bit wide quantities manipulable in a single instruction.
It just so happens that we hit a sweet spot for many years with "32-bit" x86 which had 32-bit integers and pointers, but the subtleties of classifying a system as being n-bit remain.
That said, some systems (mostly mainframes/supercomputers) are "true 64/64-bit" with 64-bit registers and 64-bit address space.
Even defining the address space is not trivial, with things like virtual vs. physical ("32-bit" x86 since the Pentium Pro actually has 36-bit physical addresses) and bankswitching (common on MCUs).
Likewise, data width is equally as complex: the Z80, commonly known as 8-bit, actually has operations on 16-bit "register pairs". 32-bit x86 with MMX has 64-bit registers, and with x87 has 80-bit wide quantities manipulable in a single instruction.
It just so happens that we hit a sweet spot for many years with "32-bit" x86 which had 32-bit integers and pointers, but the subtleties of classifying a system as being n-bit remain.
That said, some systems (mostly mainframes/supercomputers) are "true 64/64-bit" with 64-bit registers and 64-bit address space.