1.1 Systems Architecture

Question 1

The fetch-decode-execute cycle

Answer 1

The complete process of retrieving an instruction from storage, decoding it and carrying it out.

Question 2

The Fetch step

Answer 2

-The program counter holds the address of the next instruction
-The address is copied in the MAR
-the address bus goes to the value in the MAR
-the data in the location is sent along the data bus and into the MDR
-data is copied into the instruction register

Question 3

The Decode step

Answer 3

-Works out what the instructions mean

Question 4

The Execute step

Answer 4

-A signal is sent along an address bus to the memory location
-data is transferred along a data bus to the accumulator
-the program counter increments by 1

Question 5

CPU

Answer 5

The Central Processing Unit
-The internal hardware component of the computer that is responsible for executing the instructions of programs and to control the rest of the computer system
-consists of six main components: CU, ALU, registers, cache, buses, clock

Question 6

ALU

Answer 6

Performs calculations and logical comparisons in the CPU

Question 7

CU

Answer 7

The Control Unit
-It decodes instructions and sends signals to control how data moves around the CPU.

Question 8

Cache

Answer 8

Memory in the processors that provides fast access to frequently used instructions and data
-speeds up processing time as the data and instructions don’t have to be fetched directly from RAM.

Question 9

Registers

Answer 9

Tiny areas of extremely fast memory located in the CPU, normally designed for a specific purpose where data or control information is stored temporarily. Includes the program counter, MAR, MDR, accumulator, instruction register
-8-bit CPU has 8 bit registers

Question 10

How do registers increase processing speed

Answer 10

-used to hold temporary data while a software program is running
-as the CPU processes the data, the software program will shift data in and out of the registers as it is easier than in and out of cache or RAM - speeds up processing time

Question 11

Program counter

Answer 11

Holds the address of the next instruction. Step 1 of the fetch-execute cycle
-as each instruction is processed, the software that is running updates the program counter with the address of the next instruction to fetch.

Question 12

MAR

Answer 12

Memory Address Register. Holds the address of data ready to be used by the MDR or the address of an instruction passed from the program counter.
-Every instruction data in main memory is located at a unique address

Question 13

MDR

Answer 13

Memory Data Register. Holds data fetched from or to be written to memory. Step 2 of the fetch-execute cycle.

Question 14

Accumulator

Answer 14

Holds the result of calculations.

Question 15

Clock

Answer 15

The clock is the electronic unit that synchronizes related components by generating pulses at a constant rate.
-single tick - CPU processing one instruction

Question 16

Clock speed

Answer 16

Clock speed is the frequency at which the internal clock generates pulses.
-Clock speed of 3 GHz = 3 billion instructions per second.

Question 17

Bus

Answer 17

Data bus - carries data around the system
Address bus - carries info on where the data needs to go/ where the data comes from
Control bus - carries signals round the system to control components (e.g. DVD drive, hard disks, graphic cards)

Question 18

Common characteristics that affect CPU performance

Answer 18

-Clock speed
-Cache size
-No. of cores

Question 19

How clock speed affects CPU performance

Answer 19

The higher the clock rate, the faster the computer may work

Question 20

How cache size affects CPU performance

Answer 20

The larger the cache, the more data can be stored without having to go back to main memory

Question 21

How the no. of cores affects CPU performance

Answer 21

A CPU can have one or more processing units. Each unit is called a core, which contains an ALU, CU and registers
-CPUs with multiples cores have more power to run multiple programs at the same time
-having two cores will not double a computer’s speed, they have to communicate with each other through channels, which uses up some speed

Question 22

No. of cores - multitasking

Answer 22

With 2 cores, a CPU can run 2 tasks at the same time

Question 23

No. of cores - parallel processing

Answer 23

When a single task (program) is split in 2 or more parts and each part is processed at the same time.
-however, it is not always twice the speed as some programs don’t neatly split into 2

Question 24

Embedded systems

Answer 24

A computer built to solve a highly specific problem and not easy to change (A computer system that is built into another device)
-e.g. operating system placed inside a washing machine, microwave, traffic lights

Question 25

Advantages of embedded systems

Answer 25

-Small
-Built on a single circuit board so when they break, easy to replace
-use less power than general purpose computer
-designed with 1 task in mind - efficient

Question 26

Disadvantages of embedded systems

Answer 26

-if embedded computer goes wrong, equipment most likely stop working
-if fails, might have to go to a specialist supplier for replacement

Question 27

Van Neumann Architecture

Answer 27

Traditional computer architecture that forms the basis of most digital computer systems.
Instructions are fetched, decoded and executed.