how does a wider data bus helps a CPU when internal register size is smaller?

What advantage did we have in using a wider external data bus, say 64 bit in fir开发者_如何学编程st Pentium produced in 1993, when the size of the internal data bus or registers was 32 bit only?

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General purpose registers may be only be 32 bits, but there are wider registers, e.g. floating point, MMX, SSE, which may be 64 bits or more.

Note also that whole cache lines are read/written from/to memory.

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From Chapter 23 of 'The x86 PC Assembly language, Design and Interface' by Muhammad Ali Mazidi:

In the pentium, the external data buses are 64 bit, which will bring twice as much code and data into the CPU as the 486. However, just like the 386 and 486, Pentium registers are 32 bit. Bringing in twice as much as information can work only if there are two execution units inside the processor, and this is exactly what Intel has done.