Hardware

Question 1

Name the hardware elements of a computer

Answer 1

Input Devices, Processor, Output Devices, RAM Cache Memory, RAM, ROM, External/Backing store

Question 2

What is RAM?

Answer 2

RAM (Random Access Memory) is memory which holds program instructions (e.g. word processor, games) and data (the document being edited, the score of a game etc.)

Question 3

What happens to RAM when power is removed?

Answer 3

RAM is volatile meaning data will be lost if power is removed.

Question 4

What happens to programs in RAM to be executed?

Answer 4

They are first loaded from backing store (e.g. disk) before being ran. This is because RAM is much faster (and more expensive)

Question 5

Name one of the programs held in RAM

Answer 5

Operating System

Question 6

What does ROM do?

Answer 6

ROM holds a simple operating system (BIOS) ‘burnt’ onto the chip at the time of manufacture.

Question 7

What does the BIOS do?

Answer 7

BIOS (basic input output system) is a simple operating system burnt onto ROM at the time of manufacture.

The BIOS runs a ‘bootstrap loader’ that looks for another operating system (e.g. Windows, Linux) to load into RAM from backing store.

Question 8

What happens to ROM when power is removed?

Answer 8

ROM is non-volatile so data will remain when power is removed

Question 9

Draw the Von Neumann architecture with names on each component.

Answer 9

Check if correct slide 4

Question 10

What is the CPU and what does it do?

Answer 10

The CPU is the Central Processing Unit.

It controls the transmission of data to and from main memory. Processes the data in memory. Controls the transfer of data between input, output and main memory.

Question 11

Name the components of a CPU and what each of them do.

Answer 11

Control Unit - Fetches each instruction in sequence from memory, decodes and synchronises it before executing it by sending control signals to other parts of the computer.

Arithmetic Logic Unit (ALU) - Carries out the processing and manipulation of data which normally consists of arithmetic operations (addition, multiplication, etc.) or logical comparisons (AND, OR, XOR, etc.)

General Purpose Registers - Temporary memory locations within the CPU. Used when a program instruction is being carried out to hold temporary values.

Instruction Set - all the program commands available within a particular CPU.

Question 12

Name all the Special Registers and what they do

Answer 12

MAR (Memory Address Register) - Holds the address of the memory location currently being accessed.

MDR (Memory Data Register) - Holds the data read from (or to be written to) memory

PC (Program Counter) - The address of the next program instruction to be read from memory.

CIR (Current Instruction Register) - The instruction most recently fetched from memory.

Question 13

What is a bus?

Answer 13

Buses are collections of wires inside the computer which transmit information between the components and also to input/output devices. There are three different bus types.

Question 14

Name the three different buses and what they do

Answer 14

Address bus - Used to specify the address in memory where data will be read from or written to.

Data bus - This is used to transfer data from memory into the CPU (e.g. a program instruction or an item of data) or from CPU back to memory.

Control Bus - Used to send control signals between parts of the computer. One key example is it specifies whether the data is being written to or read from memory.

slides 8 and 9 for examples of read/write of the buses.

Question 15

Give examples of an input device

Answer 15

Keyboards, touch screen, voice input, biometrics, mouse, joystick, pen/stylus input, touchpad.

Question 16

Give examples of an output device

Answer 16

Monitors, printers, sound, voice, control (e.g. switching on heating, opening curtains)

Question 17

What are the advantages of speech recognition (speech input)?

Answer 17

• No need to type
• Faster input as most people can speak faster than they can type
• Useful for some people with disabilities
• Useful when hands are occupied doing another task

Question 18

What are the disadvantages of speech recognition (speech input)?

Answer 18

• Background noise can cause problems
• People overhear what you are saying
• Can make a noisy work environment
• May take time for the system to learn the users accent
• Could misunderstand people with colds, speech impediments etc.

Question 19

What are the advantages of Speech Synthesis (speech Output)?

Answer 19

• Computer able to read documents, books etc.
• Useful for partially sighted/blind people or people who cannot read
• Could be used to learn pronunciation of words
• Information warnings (e.g. lift doors closing)
• No need to look at screen (useful for Satnav)

Question 20

What are the Disadvantages of Speech Synthesis (speech Output)?

Answer 20

• Can often be quicker to read yourself

- The computer generated voice could sound unnatural and could emphasise certain words wrong.

Question 21

What are the advantages of Handwriting Recognition?

Answer 21

• Many people can write faster than they can type
• No need to learn to type
• Useful when there is limited space for a keyboard e.g. handheld devices

Question 22

What are the disadvantages of Handwriting Recognition?

Answer 22

• Not always 100% accurate
• Some handwriting is very difficult to interpret
• The pen interface may feel unnatural e.g. slippy surface

Question 23

What interfaces can be used for people with disabilities?

Answer 23

Depending on the disability:
Speech Recognition;
Foot controlled keyboard/mouse;
Head/eye movement detector;
Oversized keyboard;
Head stalk to press keys;
Braille key overlays;
Screen readers (speech synthesis);
Large/clear fonts;
Clear colour contrasts;
Braille output.

Question 24

Name all of the registers/devices that are going to be used in the Fetch execute cycle

Answer 24

Program Counter (PC) - an incrementing counter that keeps track of the memory address of which instruction is to be executed next…

Memory Address Register (MAR) - the address in main memory that is currently being read or written

Memory Data Register (MDR) - a two-way register that holds data fetched from memory (and ready for the CPU to process) or data waiting to be stored in memory

Current Instruction register (CIR) - a temporary holding ground for the instruction that has just been fetched from memory

Control Unit (CU) - decodes the program instruction in the CIR, selecting machine resources such as a data source register and a particular arithmetic operation, and coordinates activation of those resources

Arithmetic logic unit (ALU) - performs mathematical and logical operations

Question 25

Summarise the fetch decode execute cycle.

Answer 25

1. PC holds the address of the first program instruction Fetch 2. Copy value in PC intro the MAR 3. Control Bus is set to Read 4. The data (instruction) in the address specified in the MAR is fetched into MDR 5. As the MDR holds an instruction it is copied into the CIR 6. The PC is incremented (has 1 added to it) Decode 7. The instruction is decoded by the control unit so it knows which instruction it needs to execute Execute 8. The instruction/command is executed 9. Go back to step 2 Try fetch decode cycle on slide 30

Question 26

What is RAM Cache Memory?

Answer 26

Cache is small, extremely fast memory Placed near or on the processor. Data and instructions that are used regularly are stored in cache and retrieved by the processor when necessary. When the cache is full least recently used data is discarded. Caching systems will try to predict the next instructions to be accessed and pre-fetch them into the cache. Algorithms try to avoid a cache miss (when data has to be fetched from main memory rather than cache). Cache memory attempts to solve the “Von Neumann Bottleneck”. CPUs are so fast that data from RAM can’t be fetched quickly enough to keep them occupied. Cache memory helps with this by providing data more quickly.

Question 27

How does cache work?

Answer 27

Data being read from RAM is copied into the cache - it records the address the data came from, the data itself and a timestamp of when it was accessed.

Question 28

What does disk cache do?

Answer 28

This works in a similar way to RAM cache by keeping copies of blocks of data in RAM so that recently accessed blocks can be read more quickly again from RAM rather than having to read from the slower hard disk. As RAM is so much faster than Disk, there is no need to use special more expensive cache memory for a disk cache.

Question 29

What is a problem with the Von Neumann architecture?

Answer 29

The program instructions and data are accessed via the same data and address buses. That's why modern processors use a modified Harvard architecture which has separate instruction and data buses.

Question 30

What is parallel processing?

Answer 30

Parallel processing is the use of more than one processor (CPU) or processor core to perform a single task (execute a program).

Question 31

When is parallel processing useful?

Answer 31

Parallel processing is useful where large/complex calculations are being carried out e.g. image processing, weather forecasting etc.

Question 32

What is a compiler

Answer 32

A compiler converts the whole program into machine code before it is run.

Question 33

What is assembly language?

Answer 33

It is an alternative to machine language. Instead of using binary numbers for instructions, assembly language uses short words that are known as mnemonics.

Question 34

Name the basic assembly language commands and what they do

Answer 34

- LOAD R, X: Load - STOR R, X: Store - ADD: Add - SUB: Subtract - JUMP: Program jumps to address X - COMP: Compares registers BLE X: jumps to address x based on the previous comparison if less than or equal BNE X: Program jumps to address X based on the previous comparison if not equal.

Question 35

Relocatable Code

Answer 35

Programs that can be run from any memory location

Question 36

What is a linker?

Answer 36

another program that will replace the labels with the appropriate memory addresses

Question 37

Why would programmers not use assembly language?

Answer 37

- machine dependant. (meaning that if it is written for one computer it might not work on another) - long and tedious to write. - code very difficult to maintain

Question 38

why do programmers use assembly language?

Answer 38

- Ideal when execution speed is critical (e.g. boot strap loader) - More efficient than high level language programs - Requires less time for translation into machine code as assembly language is a 1 to 1 match to machine code

Question 39

What is disk fragmentation?

Answer 39

When all but the smallest files are saved to (mechanical) hard-disk they will usually take up a number of disk blocks Fragmentation occurs when the file system cannot or will not allocate enough contiguous space to store a complete file as a unit, but instead puts parts of it in gaps between existing files. Usually those gaps exist because they formerly held a file that the operating system has subsequently deleted. It will be slower to open a fragmented file as the read/write head on the disk drive has to move to load each part from a different track and mechanical movement slows the operation down.

Question 40

What is disk fragmentation?

Answer 40

When all but the smallest files are saved to (mechanical) hard-disk they will usually take up a number of disk blocks Fragmentation occurs when the file system cannot or will not allocate enough contiguous (next to eachother) space to store a complete file as a unit, but instead puts parts of it in gaps between existing files. Usually those gaps exist because they formerly held a file that the operating system has subsequently deleted. It will be slower to open a fragmented file as the read/write head on the disk drive has to move to load each part from a different track and mechanical movement slows the operation down.

Question 41

What is disk defragmentation?

Answer 41

-When necessary an operating system will automatically run a defragmentation routine which moves the blocks around to make sure that the files take up a contiguous (next to eachother) set of blocks. slide 66 for before and after defragmentation

Question 42

What are the two traditional types of cache memory?

Answer 42

RAM cache and disk cache

Question 43

What is RAM cache?

Answer 43

RAM cache is memory between the CPU and main memory where sections of data and/or programs are stored

Question 44

What is disc cache

Answer 44

Disc cache is a section of main memory between the cpu and disc where data recently read from disc or about to be written to disc is temporarily stored (before being transferred to RAM)

Question 45

What is amdahls law

Answer 45

Parallel processing time = time using a single processor system(fraction of processing which must be linear + fraction which can be run in parallel / number of processors)