# Is address bus size same as physical address size and is that the same as word size?

I am having some confusion between address bus size, physical address size and word size however (I do understand that unit of memory access is word and when word size is one byte then it's known as byte-addressable).

• I hope address bus size is same as physical address size. But there is no such constrain for the word size to be equal to the address bus size / physical address size.. But 1 thing is for sure. The address bus width should be less than the word length of the system. If it is not then the extra address bus width is of no use and that memory remains unused I hope.suppose you have a 32 bit system. Then the highest memory location address your memory can hold is 32 bit which is equivalent to a $2^{32}$ bytes memory in byte addressable system or $2^{32}\times 4$ bytes if the system is word addr – Abhishek Ghosh Aug 2 '20 at 6:36
• I appreciate your effort, but honestly I don't think my question was fully answered, I'd like to get bit more clarification on crux of the question. – Pawan Nirpal Aug 2 '20 at 7:23
• @AbhishekGhosh: I think it is quite common, especially for "ridiculously large" address sizes such as 64 bit or even 128 bit, it is quite common that the physical address size is smaller. E.g. neither the current AMD nor Intel processors actually have 64 address pins. I think they are somewhere in the high 50s at the moment. – Jörg W Mittag Aug 2 '20 at 11:48