Thread: Proccessor Registors...

Here is what I know....

EAX is a 32 bit register, and it is the same register as AX which was the "old" 16 bit register for the x86. The E stands for "Extended" I think. AH and AL are the high and low order bits of EAX, and ax on a 16 bit system is the same as AL with the 32 bit processor. This was all for backward compatibility type reasons. All these rules apply to all the other registers too.

So EAX, EBX, ECX, EDX are all general purpose registers, but each is optimized for specific purposes. EAX is the general purpse, put anything here register. It is optimized for arithmetic instructions. Of special significance is that when making function calls in c, the return value is stored in EAX. So when the function returns, EAX is never pushed and never popped, because you want the value of it to change...unless you have a void function(). EBX is optimized to hold addresses. ECX is a counter register, ie for loops, and I think there is some auto-incrementing features to this if you use some of the CISC-y instructions for looping. EDX is optimized for ....uh...gotta look at the book for this one...oh right..it is used for multiply and divide instructions..."for example, EDX holds the high 32 bits of the product" in a multiply instruction.
ESI and EDI are string registers, and they stand for destination index and source index. These two are used with the string movement instructions, so you let esi point to the source string address, and edi point to the destination addresss.

There are tons of other assembly language things to learn, this is just the surface on top of the surface. Very interesting topic though, I enjoyed the class a lot when I took it in school.

Good Luck.