module 2: Basic Computer Architecture and Principles of Operation

Question 1

Briefly describe the function of the following components of a computer:
a. ALU

b. Register array

c. Control Unit

d. Primary Memory

e. Input / Output Unit

Answer 1

a: Arithmatic Logic unit; performs arithmatic or logical operations

b: a group of memory circuits used to store binary data

c: igital circuitry that coordinates all activities in the processor

d: memory accessible by the processor e.g. RAM, ROM, Casche

e. allows data/ signal transfer between ‘external’ devices and the processor/ memory

Question 2

What is a bus?

Describe what it is (physical structure) and what it does.

Answer 2

the communications path that connects the CPU to the other components

a set of ‘wires’ that carry bits to different registers

Question 3

Name the 3 components of a system bus and describe their function.

(clue: what is the direction)

(+1 point: middle bus mentions what it transfers)

Answer 3

address bus: unidirectional bus that transmits memory addresses

data bus: bidirectional bus that transfers data to and from memory.
Transfers data, instructions, operand addresses

control bus: a bidirectional bus that times and decodes instructions with clock signals

Question 4

what is the IR and what does it do

Answer 4

Instruction register: holds the current instruction to be decoded

Question 5

what is the PC and what does it do

Answer 5

Program Counter: holds the next address to be fetched from memory

Question 6

what is the MAR and what does it do

Answer 6

memory address register: Holds address of operand to be fetched from memory

Question 7

what is the Accumulator and what does it do

Answer 7

Data register that holds an output of ALU

Question 8

what is the Address Latch and what does it do

Answer 8

temporarily holds the address that is being fetched via the address bus

Question 9

what is the Data buffer and what does it do

Answer 9

temporarily holds the data that is being read from memory via data bus

Question 10

There is a control signal called R/W . What do the symbols R, W and the (bar symbol) mean?

Describe the function of this control signal with records to primary memory.

Answer 10

R = read
W = write

the bar = not: signal is Active-low

so when the bar is over the W, the signal is low and it will do a write operation otherwise, it will do a read operation

Question 11

What is an instruction set? (give an example of an instruction within the instruction set)

Answer 11

a predefined set of instructions that a processor can perform

e.g. ADD (add to accumulator)

Question 12

In binary, the MSB refers to:
e. The number of bits in memory
a. The ‘rightmost’ bit
d. The largest bit that is a ‘1’
c. The ‘leftmost’ bit
b. The first bit that is a ‘1’

Answer 12

c. The ‘leftmost’ bit

Question 13

Non-integer numbers are stored in computers as:
b. Floating point numbers
c. Hexadecimal
a. Fractions
d. Octal
e. ASCII

Answer 13

b. Floating point numbers

Question 14

The devices or software that can convert non-textual data to binary and back are called:
c. Modems
b. Assemblers
e. Simulators
a. Accumulators
d. Codecs

Answer 14

d. Codecs

a hardware or software tool that compresses and decompresses digital media, like video and audio, to make files smaller for easier storage and transmission, and then restores them for playback or editing

Question 15

Data addressing modes are the ways in which:
a. The binary addresses are converted to integers
e. The calculations are carried out
b. The operands can be accessed by the processor
c. The address is transferred to the data bus
d. The processor accesses the instructions

Answer 15

b. The operands can be accessed by the processor

Question 16

When the data to be processed is contained in the next byte(s) of the program code, it is called:
c. Implied addressing
e. Program decoding
a. Programmed data
b. Internal addressing
d. Immediate addressing

Answer 16

d. immediate

Question 17

In _______________ format, the low-order byte of the data is stored first.

Answer 17

little endian

Question 18

The binary address 1010 0001 0100 1111 when represented in hexadecimal would be:
e. F81B h
b. F41A h
a. A14F h
d. B18F h
c. 1092B h

Answer 18

a. A14F h

Question 19

In relative program addressing mode, a constant called an offset added to the _________________.

Answer 19

Program Counter
PC register
PC

• relative
  
  • instruction specifies a value (positive or negative) that is added to the PC register
  • causes the program to move forward or backward a certain number of bytes

Question 20

A signed integer is stored in memory as 1010 1010. The value of this integer in decimal is:
86
-42
-170
-86
170

Answer 20

-86

Question 21

The part of the processor that does the computation (e.g. adding of numbers) is called the:
a Accumulator
b Instruction Decoder
c Primary Memory
d ALU
e Program Counte

Answer 21

ALU

Question 22

The system bus consists of three separate buses, which are:

a Data bus

b Control bus

c Binary bus

d I/O bus

e Address bus

Answer 22

a b e

Question 23

Clock signals are needed to:
To keep track of how long processor has been running
To work out the speed of all components
To find the most efficient operation
Synchronise the actions of different components of the system
To keep track of what time it is

Answer 23

Synchronise the actions of different components of the system

Question 24

What the processor does continuously from the time it is switched on till it is switched off is:

the boot sequence
the fetch-decode-execute cycle
the I/O process
the computation process
the duty cycle

Answer 24

the fetch-decode-execute cycle

Question 25

An instruction set is: The process of reading an instruction into the processor The number of instructions in a program The current instruction that is being executed The set of operations that a processor can perform The number of bits in the instruction register

Answer 25

The set of operations that a processor can perform

Question 26

Which of the following is NOT true about computer memory? It is normally organised in bytes It only contains binary data Each memory location has an address The Read/ Write signal line is used to transfer data It is a place to store information

Answer 26

The Read/ Write signal line is used to transfer data

Question 27

The Program Counter (PC) Contains the number of operands to be fetched Stores the number of instructions in a program Add the numbers in a program Stores the results of computation Contains the address of the next instruction to be fetched

Answer 27

Contains the address of the next instruction to be fetched

Question 28

When an instruction is being executed: The opcodes are sent to the accumulator The timing and control unit generates a series of control signals The instruction is transferred from memory to the instruction register The program counter is decremented The decoder interprets signals on the data bus

Answer 28

The timing and control unit generates a series of control signals

Question 29

An instruction for the processor can be broken into two parts, the __________ tells it what to do and the ________ specifies what to do it with. Hint: Both answers start with the same letter.

Answer 29

Answer 1: opcode operation Answer 2: operand

Question 30

The execution of an instruction can be broken down into smaller steps. These steps are defined in the ________ run by the Control Unit.

Answer 30

microcode microprogram