processor components

Question 1

central processing unit (CPU)

Answer 1

it is also simply known as the main processor, contains a different number of components which enables it to carry out its tasks of executing instructions

Question 2

describe the CU (control unit)

Answer 2

the control unit controls and coordinates the activities of the CPU. It accepts the next instruction, decodes it in several sequential steps such as fetching address and data from memory, manages its execution and stores the resulting data back in memory of registers

Question 3

describe buses

Answer 3

a bus is a set of parallel wires connecting two or more components of a computer. it typically consists of 8, 16, 32, 64 lines.

Question 4

describe control bus

Answer 4

the control bus is a bi-directional bus, meaning that signals can be carried in both directions.

control lines include:
bus request: indicates that device is requesting the use of the data bus
bus grant: indicates that the CPU has granted access to the data bus
memory write: causes data on the data bus to be written into the addressed location
memory read: causes data from the addressed location to be placed on the data bus
interrupt request: indicates that a devices is requesting access to the CPU
Clock: used to synchronise operations

Question 5

describe the Data Bus

Answer 5

The data bus, typically consisting of 8, 16, 32, 64 separate lines, provides as bi-directional path for moving data and instructions between system components

Question 6

describe the Address bus( what is a word? )

Answer 6

the address bus transmits the memory address of words that are use as operands in programs. a word is a fixed size group of digits, typically 16, 32 or 64 bits. this is handled as a unit by the processor. each word in memory has its own specific address.

Question 7

what does the Arithmetic-logic Unit (ALU)

Answer 7

the Arithmetic-logic Unit performs arithmetic and logical operations on the data. it can perform instructions like ADD, SUBTRACT, MULTIPLY, DIVIDE on fixed or floating point numbers. it can also perform shifts.

Question 8

Registers

Answer 8

are special memory cells that operate at very high speed

Question 9

describe the program counter (PC)

Answer 9

it is a register that holds the next instruction that is going to be executed

Question 10

current instruction register (CIR)

Answer 10

it is a register that holds the current instruction that is being executed

Question 11

memory address register (MAR)

Answer 11

its a register that holds the address of the current instruction which is being executed

Question 12

memory data register (MDR)

Answer 12

its a register that holds the data of the current instruction which is being executed

Question 13

The Fetch-Decode-Execute cycle

Answer 13

the sequence of operations involved in executing an instruction can be divided into three phases - fetching, decoding and executing it. this repeats until all of the instructions have been executed

Question 14

what happens in the fetch phase

Answer 14

1. The address of the next instruction is copied from the PC to the MAR
2. The instruction held at that address is copied to the MDR. simultaneously, the PC is incremented by 1
3. The contents of the MDR are copied into the CIR

Question 15

what happens in the decode phase

Answer 15

the instructions held in the CIR is decoded. The instruction is split into OPCODE and OPERAND. the opcode is used to determine the type of instruction and what hardware to use to execute it.

1. the address of the data to be used with the operation, which is then copied to the MAR
2. the actual data to be operated on, which will be copied to the MDR
3. the data to be operated on may be passed to the ALU/ accumulator