4.7.3 Structure and Role of the Processor

Question 1

Which type of register is the status register: general purpose or special
purpose?

Answer 1

Special purpose

Question 2

Which of the following is not found within a processor?
A: Control unit
B: Main memory
C: Buses

Answer 2

B: Main memory

Question 3

What effect does increasing the width of the address bus have?

Answer 3

Increases the computer’s amount of addressable memory

Question 4

Which register holds the instruction that is currently being executed by the
processor?

Answer 4

Current instruction register

Question 5

What is cache?

Answer 5

A small portion of fast memory used to store frequently used information in the processor.

Question 6

What name is given to small storage locations used to hold data temporarily in the processor?

Answer 6

Registers

Question 7

What is meant by this assembly language instruction?
STR R3, 38

Answer 7

Store the value that is in register 3 into
memory location 38.

Question 8

Which register holds the contents of a memory location that has been read from or data that is to be stored?

Answer 8

Memory buffer register

Question 9

Which part of a computer’s processor generates signals at a regular frequency?

Answer 9

Clock

Question 10

Which special purpose register is abbreviated as MAR?

Answer 10

Memory address register

Question 11

Name the three stages of the fetch-execute cycle

Answer 11

Fetch, decode, execute

Question 12

Form an assembly language instruction that would mean: “Add the value in register 4 to the value in register 5 and store the result in register 3”

Answer 12

Form an assembly language instruction that would mean: “Add the value in register 4 to the value in register 5 and store the result in register 3”
ADD R3, R4, R5

Question 12

What name is given to the data to be used in an instruction: opcode or operand?

Answer 12

Operand

Question 13

In which stage of the fetch-execute cycle
is the program counter incremented?

Answer 13

Fetch

Question 14

Between which two stages of the fetch-execute cycle is the status register checked?

Answer 14

Execute and Fetch

Question 15

In which addressing mode does the value specified by an operand signify a memory address?

Answer 15

Direct Addressing

Question 15

What name is given to the group of
instructions that a processor can carry out?

Answer 15

Instruction set

Question 16

What name is given to a signal sent to
the processor by another part of the
computer requesting the attention of the
processor?

Answer 16

Interrupt

Question 16

In which stage of the fetch-execute cycle
is an instruction broken into opcode and operands?

Answer 16

Decode

Question 17

What is Address Bus Width?

Answer 17

• Width of bus relates to number of parallel wires that make up the bus.
• Increasing the width of the address bus increases the range of addresses that it can specify, increasing computer’s amount of addressable memory.
• Adding a single wire doubles the number of addressable memory locations

Question 18

What is Data Bus Width?

Answer 18

• Increasing width of data bus increases the volume of data that can be transferred over the bus at any one time.
• A wider data bus allows Processor to fetch more data from main memory in one cycle of the FDE cycle, reducing number of cycles needed to fetch large volumes of data.

Question 19

Detail the Check for Interrupts

Answer 19

• Between each execute stage and fetch stage of the FDE cycle, the content of the status register is checked
• The Status Register (SR) is checked for changes that could signify the occurrence of an interrupt.

Question 20

Detail the parts of this:

0 1 1 0 1 1 0 1

Answer 20

Opcode: 0110
Operation: 011
Addressing Mode: 0 (4th one)
Operand: 1101

Question 21

What is the Control Bus?

Answer 21

• Bi-directional bus
• Data and Address buses are shared by all components of the system. Control lines must therefore be provided to ensure that access to and use of these buses by different components doesn’t lead to conflict.
• Control Line examples could be: Memory Write, Interrupt Request, Bus Grant, Reset etc.

Question 21

What is the Data Bus?

Answer 21

- Bi-Directional - Typically has 8, 16, 32, 64 separate lines - Width of the data bus is a key factor in determining overall system performance: - If data bus is 8 bits wide, and each instruction is 16 bits long, the processor must access the main memory twice just to fetch the instruction. - Transfers data between a computer's memory and its CPU

Question 22

What is Clock Speed?

Answer 22

- Clock Speed relates to frequency of the pulses generated by system clock - Increased frequency means more FDE cycles can be completed in same period of time. - Errors can occur when Computer's clock speed is increased too far

Question 22

What is the Address Bus?

Answer 22

- One-Directional (unidirectional) Bus - Memory is divided internally into units called Words - Each word in memory has its own specific address - When processor wishes to read a word of data from memory it first puts the address of the desired word on the address bus. - The width of the address bus determines the maximum possible memory capacity of the system. For example: if the address bus had only 8 lines, the maximum address it could transmit would be 255 or 11111111 in binary. Giving max of 256 including address 0. - Address bus is also used to address I/O ports during input/output operations.

Question 22

What are the three electronic circuits making up I/O Controller

Answer 22

The Controller is an electronic circuit board consisting of 3 parts: 1) An interface that allows connection of the controller to the system 2) A set of data, command and status registers. 3) an interface that enables connection of the controller to the cable connecting the device to the computer.

Question 23

What is Number of Cores?

Answer 23

- Directly affects computer performance - each core can do the FDE cycle independently - different applications for different cores - quad-core and octo-core now more common

Question 23

What is an I/O controller?

Answer 23

- An I/O Controller is a device which interfaces between an input or output device and the [processor. Each device has a separate controller which connects to the control bus. - The I/O controllers receive input and output requests from the processor and then send device-specific control signals to the device they control. - They also manage the data flow to and from the device - The Controller is an electronic circuit board consisting of 3 parts.

Question 23

What is Word Length?

Answer 23

- A word is a group of bits treated as a single unit by the processor - Fixed size group of digits, typically 8, 16, 32 or 64 bits. - Words can be used to represent both instructions and data - Length of word is the number of bits assigned to it - More word length allows for more bits to be transferred and manipulated as a single unit

Question 24

What is the Program Counter (PC)?

Answer 24

- Used to hold memory address of the next instruction to be executed in FDE cycle.

Question 24

What is Cache Memory?

Answer 24

- processor's cache is small portion of incredibly fast memory - read and write speeds far higher than hard disk drives or SSDs. Cache used to store frequently used information, reducing time wasted from fetching instruction every time from main memory. - More Cache of processor has, more information it can store, more time to can save fetching info from main memory.

Question 25

What is the Current Instruction Register (CIR)?

Answer 25

- Holds the instruction that is currently being executed by the processor.

Question 26

What is the Memory Address Register (MAR)?

Answer 26

- Stores Memory Address of a Memory Location that is to be read from or written to

Question 27

What is the Memory Data Register (MDR)?

Answer 27

- Also called Memory Buffer Register (MBR) - Holds the contents of a memory location that has been read from or data that is to be stored.

Question 28

What is the Status Register (SR)?

Answer 28

- Contains a number of bits - Provides information about the result of the last instruction - To control conditional branch instructions - Checks the value of the bits which can indicate the occurrence of an interrupt

Question 29

What is the Clock?

Answer 29

- Inside a CPU is the system clock - System clock generates a timing signal which changes at a regular frequency. - This signal is used to synchronise communication between the components of the processor and the rest of the computer system.

Question 30

Detail the FETCH Stage of the FDE

Answer 30

1) Contents of the PC is copied to the MAR 2) Contents of the MAR is transferred to main memory by the address bus 3) The instruction is sent from main memory to the MDR by the data bus 4) The PC is incremented by one 5) THe content of the MDR is copied to the CIR

Question 31

Detail the DECODE Stage of the FDE

Answer 31

1) The contents of the CIR is decoded by the control unit (CU) 2) The decoded instruction is split into two parts: opcode and operands

Question 32

Detail the EXECUTE Stage of the FDE

Answer 32

1) Any data required by the instruction that isn't present in registers is fetched 2) The instruction is carried out 3) Results of any calculations are stored in general purpose registers or main memory

Question 33

What is a Bus?

Answer 33

A set of parallel wires connecting two or more components of a computer

Question 34

What is Von Neumann Architecture?

Answer 34

- Both data and instructions are held in the same memory. - E.g.: 10 * 12, all get stored in one set of memory, one set of buses. Memory and Data are stored in the same memory.

Question 35

What is Harvard Architecture?

Answer 35

- Two sets of memory, two sets of buses for Harvard. Memory and Instructions are stored in different memory. - E.g.: 10 12, 10 and 12 in data whereas the () in instructions.

Question 36

What is an Interface?

Answer 36

- A standardized form of connection defining such things as signals, number of connecting spins/sockets and voltage levels that appear at the interface. - An example is a Universal Serial Bus (USB) connection, which can be used with many different peripherals.

Question 37

What is a General Purpose Register?

Answer 37

- Up to 16 general purpose registers in CPU - All arithmetic, logical or shift operations take lace in registers. - Another word for Accumulator

Question 37

What is the stored program concept?

Answer 37

- Program Instructions are transferred from backing store to main memory - Program consists of a sequence of instructions - Program is stored in main memory and can be replaced by another program at any time - Instructions are fetched in sequence, decoded and then executed.

Question 38

Direct Consequence of increasing data bus width?

Answer 38

- Increases the number of bits that can be transferred at one time - Increased rate of data transfer

Question 39

Direct Consequence of increasing address bus?

Answer 39

- Increases the number of memory addresses, addressable locations - Increase the maximum amount of primary storage

Question 40

What is the difference between RISC and CISC processors?

Answer 40

RISC (Reduced Instruction Set Computing): Uses a small, simple set of instructions that can be executed quickly. CISC (Complex Instruction Set Computing): Uses a larger, more complex set of instructions, which may take longer to execute but can perform more work in a single instruction.

Question 41

What is an interrupt in the context of a processor?

Answer 41

An interrupt is a signal that temporarily halts the processor's current operation to address a higher-priority task or event (such as I/O operations), after which the processor returns to its previous task.

Question 42

What is the Stored Program Concept?

Answer 42

The Stored Program Concept refers to the idea that a computer's program instructions (code) and the data it processes are both stored in the computer’s memory, allowing the processor to fetch and execute instructions sequentially.

Question 43

What are peripherals in computing?

Answer 43

Peripherals are external devices that are connected to a computer to provide additional functionality or enhance the capabilities of the computer. They can be input devices, output devices, or storage devices.

Question 44

Draw Diagram of FDE Cycle

Answer 44