1.1 The characteristics of contemporary processors, input, output, and storage devices

Question 1

control unit

Answer 1

part of processor that controls activity of all other components

. directs flow of data between CPU and other devices
. carries out next instruction
. sends memory read and write requests to main memory on control bus and other command and control signals
. makes extensive use of the status registers and clock
. coordinates and communicates with all parts of the CPU

Question 2

Buses

Answer 2

consists of a series of connectors that transfer signals between internal components. consists of 8,16,32,64 lines

Question 3

system bus

Answer 3

consists of three separate buses carrying control signals, addresses and data

Question 4

control signals include:

Answer 4

memory read
memory write
bus request
bus grant
clock

Question 5

Memory read

Answer 5

causes data from the addressed location in RAM to be placed in a data bus

Question 6

Memory write

Answer 6

causes data on data bus to be written into the addressed location in RAM

Question 7

Bus request

Answer 7

indicates that a device is requesting use of data bus

Question 8

Bus grant

Answer 8

shows CPU has granted access to the data bus

Question 9

Clock

Answer 9

Used to synchronise operations

Question 10

Arithmetic logic unit (ALU)

Answer 10

the problem solving part of the processor. Performs arithmetic, logical and shift operations on data

Question 11

Program counter (PC)

Answer 11

holds the address of the next instruction to be executed

. could be next instruction in a sequence
. could be address to jump or branch - this would be copied from CIR

Has a very close relationship with the MAR. at the start of new FDE cycle the address held in PC is copied to MAR

Question 12

Memory address register (MAR)

Answer 12

holds the address memory location from where data or an instruction is to be fetched or where data is to be written

sends these address to memory down the address bus

Question 13

Memory data register (MDR)

Answer 13

used to temporarily store the data which is read from, or written to memory

can be knows as memory buffer register (MBR) and nicknamed gateway to the processor

all data to and from memory must travel down data bus and pass through the MDR

Question 14

current instruction register (CIR)

Answer 14

holds current instruction being carried out

contents of MDR are copied to CIR if it’s an instruction

contains opcode and operand of current instruction

instruction = opcode + operand

Question 15

Accumulator

Answer 15

One of the general-purpose registers that a CPU has

Stores data and control information

Results of calculations carried by ALU can be stored here

Question 16

Address bus (unidirectional)

Answer 16

carries from CPU to main memory

carries memory addresses that
identify where data is being read from or written to

Question 17

Data bus (bidirectional)

Answer 17

carries the binary numbers that make up the actual info being transmitted around CPU

Question 18

Control bus (bidirectional)

Answer 18

carries commands and control signals to and from everywhere in the CPU

Question 19

Computer

Answer 19

something that takes an input processes the data and produces and output

Question 20

FDE cycle - Fetch

Answer 20

PC is checked for next instruction address

Address is copied in MAR

sent along address bus to main memory and waits for control bus

Control unit sends read signal along control bus to main memory

Contents stored in address can be sent to MDR along data bus

Data received by MDR gets copied to CIR

Question 21

FDE - Decode

Answer 21

Instruction in CIR is decided by decode unit

instruction is 2 parts opcode and operand
opcode - what to do
operand - what to do it to

operand can contain actual data or the address

decode instruction and see which operation is needed

Question 22

FDE - Execute

Answer 22

send address to MAR

send address on address bus to main memory

contents stored in address is sent along data bus to MDR

contents of MDR is copied to accumulator

instruction now complete