Is the stack width always same as CPU register size?

Question

For example, for a 8-bit CPU, the stack size is expected to be 8-bit wide, and 16-bit CPU vs 16-bit stack width, and 32-bit, 64-bit CPU, and so on. Is it true for all archit

Answer 1

A CPU has a data bus and a address bus. They can have the same width, but they often aren't.

The stack pointer is a pointer to memory, so its often as wide as the address bus, unless there is some (weird/obscure) conversion used internally. The instruction pointer (points to the current instruction) is also a pointer to memory and as such as wide as the stack pointer.

Other registers mostly deal with data, and as such have the same dimensions as the data bus. But as usual, there are exceptions.

To take an old example. The 6502. A 8 bit cpu (8 bit databus, 16 bit addressbus). It has the (more or less) general purpose registers X and Y, and the "accumulator" called A. All 8 bit registers. There is a stack pointer and a instruction pointer, the stack pointer having 8 explicit and 8 implicit bits (stack is always in the same 256-byte region) and thus the stack pointer register having 8 bits, the instruction pointer having 16 bits.

The 8086, has an 16 bit databus and a 20 bit addressbus. The general registers where 8 (and 16 bit). The instruction pointer and stackpointer where 16 bit, but used segment registers (also 16 bit) to get the full 20 bit address.