Question about 64 bit processors ?

Question

Why is it that a 32 bit processor has 2^32 address spaces and a 64 bit processor only has 2^48 address spaces? What does the 32 and 64 stand for if not address spaces? It would seem that a 64 bit processor should have 2^64 address spaces.
Seeking knowldge,
Daniel
The book I am reading is explaining this all in a metaphor so I'm not 100% sure I am using the correct term 'address spaces'.

Answer 1

the number of bits refers to how much data can be stored in the 'registers', which are the storage area used to hold data and addresses. a 32 bit processor can only work with 32 bits, or 4 bytes at a time, a 64 bit processor can double that. and yes, in theory a 64 bit procrssor can directly address 2^64 bytes of memory. the main impact of 64 bit is that the processor can work with twice as much data for each clock cycle which makes things faster, but not twice as fast.

Answer 2

each processor has registers, a bit like your handheld

calculator that people no longer bother with



the 64 bits refers to the width of the registers in bits,

so it represents the width of data that can be processed

with a single processor instruction so you can

add two 64 bit registers together or multiply two 64 bit

registers and so on.



it is not really to do with RAM anymore because you can

attach as much or as little as you like, and even employ

clever memory access techniques with new memory

handling hardware, so address space can no longer

be related to processor BIT WIDTH.



so its about REGISTER WIDTH

Answer 3

Basically



Here is the best layman explanation I can muster.



Information moves in 8 wires, also known as 8-bit data. 8bits is a byte of a single pice of data.

A 32 -bit CPU can take in 4 pieces of data at once, 4 pieces * 8 bits = 32-bit.

A 64-bit CPu can take in 8 pieces of data at once, so to really sum it up the difference is the amount of data that the processor can receive in a single clock beat.



A 32-bit 2.4Ghz CPU can read 76,800,000,000 bits or 9,600,000,000 bytes (characters) in a second.



A 64-bit 2.4Ghz CPU can read 153,600,000,000 bits or 19,200,000,000 bytes(characters) in a second.



To sum it up, the 64-bit CPUS, even with the same Ghz clock rating can process twice the information that a 32-bit CPU can.