Von Neumann

Question 1

What is the von Neumann model and how many components does it have?

Answer 1

A fundamental model of a computer for processing computer programs.
5.

Question 2

instruction

Answer 2

the smallest piece of work specified in a computer program

Question 3

Address space

Answer 3

The total number of memory locations (“boxes”) available.

Question 4

MAR

Answer 4

memory address register;
address of location to be accessed
sets up the decoder circuitry in the memory.

Question 5

Addressability

Answer 5

he number of bytes of memory referenced by a given address.

Question 6

MDR

Answer 6

memory data register;

where the contents of the MAR is placed into.

Question 7

How to store a value in a memory location

Answer 7

First, write the address of the memory location in MAR, and the value to be stored in MDR. Then, go through the computer’s memory with the WE signal asserted. The information contained in the MDR will be written onto the memory location in MAR.

Question 8

Processing unit

Answer 8

A unit in the vM model that does the instructions, specializing in one complex function.

Question 9

What are the basic components of a processing unit?

Answer 9

ALU and General Purpose Registers (TEMP)

Question 10

ALU

Answer 10

The Arithmetic and Logic Unit;
capable of performing basic arithmetic.
The ones for LC-3 include ADD, AND, NOT and Pass Through

Question 11

What is the word length of the LC-3?

Answer 11

16 bits

Question 12

Word length

Answer 12

Size of the quantities normally processed by the ALU

Question 13

Which ISAs have their own word length, and what does it depend on?

Answer 13

All of them.

It depends on the intended use of the computer

Question 14

What are the Registers (TEMP) used for on the Processing unit?

Answer 14

Fast “on-board” storage for a small number of words.

Close to the ALU allows for intermediate data storage while processing (much faster access than RAM).

Question 15

Control unit

Answer 15

Keeps track of which instruction is being executed.

It fetches & decodes each instruction, and sets up the appropriate inputs for the Memory, Processing, and I/O.

Question 16

PC

Answer 16

Program Counter, aka the Instruction Pointer;

Holds the address of the next instruction to be fetched.

Question 17

IR

Answer 17

Instruction Register,

Holds the instruction currently being executed.

Question 18

Steps of Fetch

Answer 18

PC -> MAR
PC -> PC + 1
Mem[MAR} -> MDR
MDR -> IR

Question 19

Fetch

Answer 19

Read an instruction from memory.

Question 20

Decode

Answer 20

Examines the instruction in order to figure out what the microarchitecture is being asked to do

Question 21

Evaluate address

Answer 21

Computes the address of the memory location that is needed to process the instruction

Question 22

Fetch operands

Answer 22

Obtains the source operands needed to process the instruction.
Operands can come from Registers or RAM, or be embedded in the instruction itself.

Question 23

How is the Effective Address (EA) determined?

Answer 23

By the Evaluate address step;
computing the address of the operand (if any), or of the memory location to be accessed: e.g. the location from which to obtain a value.

Question 24

Where do you store results?

Answer 24

Register or Memory
e.g.
LD.REG
MEM.EN/W

Question 25

Do all instructions require all six steps? If not, which and why?

Answer 25

No.
If only using registers, skip Evaluate Address
If only moving data, skip Execute

Question 26

Types of instructions

Answer 26

Data movement, Control, and Operate