What does ESP mean in assembly?

Question

ESP = ? stack pointer

What does E stand for here?

UPDATE

RSP for 64bit?

What does R mean here?

Solution 1

E stands for Extended

With the advent of the 32-bit 80386 processor, the 16-bit general-purpose registers, base registers, index registers, instruction pointer, and FLAGS register, but not the segment registers, were expanded to 32 bits. This is represented by prefixing an "E" (for Extended) to the register names in x86 assembly language.

Source

Solution 2

R is just for "register", with the new registers called just r8-r15. Since the old ones also needed names for their extended versions, the e was just swapped to r.

Solution 3

Perhaps for consistency with the other 32-bit registers: EAX, EBX etc.

For those, E means "extended" - i.e. to 32 bits (the 16-bit versions are called AX, BX etc.)

P.S. according to The Free Dictionary, ESP stands for Extended Stack Pointer.