CPU Registers

Question 1

EAX

Answer 1

It’s called the accumulator register because it’s the primary register used for common calculations (such as ADD and SUB). While other registers can be used for calculations, EAX has been given preferential status by assigning it more efficient, one-byte opcodes.

Question 2

AX

Answer 2

Least significant 16 bits of EAX

Question 3

AH

Answer 3

8 most significant bits of AX

Question 4

AL

Answer 4

8 least significant bits of AX

Question 5

EBX

Answer 5

In 32-bit architecture, EBX doesn’t really have a special purpose so just think of it as a catch-all for available storage

Question 6

BX

Answer 6

Least significant 16 bits of EBX

Question 7

BH

Answer 7

8 most significant bits of BX

Question 8

BL

Answer 8

8 least significant bits of BX

Question 9

ECX

Answer 9

The counter register. the counter (or count) register is frequently used as a loop and function repetition counter, though it can also be used to store any data

Question 10

CX

Answer 10

16 least significant bits of ECX

Question 11

CH

Answer 11

8 most significant bits of CX

Question 12

CL

Answer 12

8 least significant bits of CX

Question 13

EDX

Answer 13

The data register. EDX is kind of like a partner register to EAX. It’s often used in mathematical operations like division and multiplication to deal with overflow where the most significant bits would be stored in EDX and the least significant in EAX. It is also commonly used for storing function variables.

Question 14

DX

Answer 14

16 least significant bits of EDX

Question 15

DH

Answer 15

8 most significant bits of DX

Question 16

DL

Answer 16

8 least significant bits of DX

Question 17

ESI

Answer 17

The source index. The counterpart to EDI, ESI is often used to store the pointer to a read location

Question 18

EDI

Answer 18

The destination index. Though it can be (and is) used for general data storage, EDI was primarily designed to store the storage pointers of functions, such as the write address of a string operation

Question 19

EBP

Answer 19

The base pointer. EBP is used to keep track of the base/bottom of the stack. It is often used to reference variables located on the stack by using an offset to the current value of EBP, though if parameters are only referenced by register, you may choose to use EBP for general use purposes

Question 20

ESP

Answer 20

The stack pointer. ESP is used to track the top of the stack.

Question 21

EIP

Answer 21

Instruction pointer. EIP points to the memory address of the next instruction to be executed by the CPU