7 - Von Neumann's Model & Registers

Question 1

Give 4 main points of Von Neumann’s Model

Answer 1

1. General purpose machine controlled by an executable program
2. which is a list of instruction used to direct a task
3. Both the program and data are stored in machine’s memory in binary
4. A processor is therefore actively used to execute the program’s instructions

Question 2

Give the 3 principle components of a computer?

Answer 2

CPU, main memory, IO units.

Question 3

What are buses ?

Answer 3

A bus is a bundle of conductors, wires, or tracks that connects various components in the motherboard.

Question 4

Give examples of (types of) buses?

Answer 4

Address, data and control buses.

Question 5

Give advantages and disadvantage of a bus vs point-to-point connections ?

Answer 5

• The number of wires required for a bus is much smaller than for point-to-point connections. As the number of components grows, so does the wiring. Once you’re at 20-30 components, checking if everything’s connected is complicated.
• It’s easy to add new devices to a bus as it runs through the middle.
• A bus can only transfer one item of data at a time → a limit on performance

Question 6

What are the 2 parts of a CPU ?

Answer 6

The ALU and the Control Unit. (~And memory)

Question 7

How does the IO let the CPU know when it’s ready to perform a task ?

Answer 7

It sends an interrupting signal to the cpu.

Question 8

What does IP/ PC stand for and what does it do ?

Answer 8

Instruction pointer (IP) or Program pointer (PC).

It (always) points the cpu to where the next instruction is in the memory, so that the CPU can go fetch it.

Question 9

What does AX stand for and what does it do ?

Answer 9

Accumulator Register. Very frequently used.

Used for calculations and computations by storing values in the it before you use them.

Question 10

What does IR stand for and what does it do ?

Answer 10

Instruction Register.

Its a temporary storage for the instruction we’re currently working on/executing.

Question 11

What does MAR stand for and what does it do ?

Answer 11

Memory address register. NOTE: this is not a CPU register (?)

Used to hold an address of something we want to access in memory. Its another register to hold an address of something we’ve accessed in the past.

Question 12

Describe the steps in the fetch phase ?

Answer 12

1. The address in IP register is copied onto the address bus and out to the MAR register
2. IP is incremented ready for the next cycle. IP now points to the next location in the program memory
3. Memory accesses the required location and copies the content onto the data bus
4. The CPU copies the instruction code from the data bus into the IR
5. The decoding of the instruction starts

Question 13

Describe the steps in the execute phase of MOV AX, 256 ?

Answer 13

– IP is copied to address bus and latched into memory
– IP is incremented
– The value (256) selected in memory is copied onto
the data bus
– CPU copies the value from the data bus into AX