Hardware 2

Question 1

Control Unit (CU)

Answer 1

The part of the CPU responsible for directing electrical signals to the computer, in order to execute program instructions.

Question 2

Arithmetic Logic Unit (ALU)

Answer 2

The part of the CPU responsible for performing arithmetic and logical operations.

Question 3

Registers

Answer 3

The CPU has its own memory, called memory registers. These are actually even faster to use than RAM because they are physically inside the CPU and therefore the electrical signals have a shorter distance to travel.

Size is dependent on architecture, i.e. 32-/64-bit systems.

Question 4

Downsides of Registers

Answer 4

There are a limited number and they can hold an extremely limited amount of data.

Question 5

Types of Registers

Answer 5

Special Purpose: Intended for one specific task

General Purpose: Can be used by programs as they’re compiled and turned into machine code to do all manners of tasks.

Question 6

Extended Accumulator Register (EAX)

Answer 6

32-bit wide register
Designed to be the "calculator" on the system
Can reference portions of it:
- AX for (lower) 16 bits
- AH/L for higher/lower 8 bits

Question 7

Extended Instruction Pointer (EIP 32-bit, RIP 64-bit)

Answer 7

Designed to hold the memory address of the next instruction to be executed. Used to direct the CPU to find the next bit of code.

Question 8

Stack Pointer Register (ESP)

Answer 8

Contains a memory address which points to the top of the current stack frame in RAM.

Question 9

Base Pointer Register (EBP)

Answer 9

Contains a memory address which points to the bottom of the current stack frame in RAM.

Question 10

Source Index Register (ESI)

Answer 10

Typically used to hold a memory address of data when that data is being used as a source in an operation.

For example, if you are copying data from one location to another, ESI will contain the memory address of the data you are copying.

Question 11

Destination Index Register (EDI)

Answer 11

Typically used to hold a destination memory address.

If you were to copy data from one location to another, EDI holds the memory address that the data is going to be copied into.

Question 12

Fetch-Decode-Execute (FDE) Cycle

Answer 12

1. The control unit ‘fetches’ the next instruction from RAM.
2. The control unit ‘decodes’ the instruction and retrieves the necessary data from memory and places it into the arithmetic logic unit (ALU) of the CPU.
3. The arithmetic logic unit (ALU) ‘executes’ the instruction, and operates on the data provided in the previous step.
4. The arithmetic logic unit stores the result of the execution either in a memory register or RAM.

Question 13

Sections of RAM

Answer 13

Stack & Heap

Question 14

Stack

Answer 14

Very structured and orderly memory section

Program instructions are loaded onto the stack and each function is assigned a ‘stack frame’ (memory area). The stack frame contains local variables used by the function.

At the bottom of the stack frame is the return pointer.
When the CPU enters a function, it will save the previous value of EIP to the bottom of the stack frame

When the CPU gets a ‘return’ instruction, it will load the return pointer from the bottom of the stack frame into EIP and leave the function.

Question 15

Heap

Answer 15

Unstructured area of memory that can be used to store data.

Slower to access than the stack, but you can store whatever you like without knowing beforehand the size of the data.