A-Level Computer Science

Front 1

What is the ALU and what does it do?

Back 1

The Arithmetic and Logic Unit is where arithmetic and logical operations are performed. The results are stored in the accumulator.

Front 2

What is the CU and what does it do?

Back 2

The Control Unit controls how data moves around parts of the CPU and how it moves between the CPU and memory. Instructions are decoded in the CU.

Front 3

What are registers and what do they do?

Back 3

Registers are memory locations within the processor. They work quickly so the processor can use them without a bottleneck.

Front 4

What is the PC and what does it do?

Back 4

The Program Counter always contains the address of the next instruction to be executed. It gets incremented to point to the next instruction.

Front 5

What is the ACC and what does it do?

Back 5

The Accumulator stores the results of calculations made by the ALU.

Front 6

What is the MAR and what does it do?

Back 6

The Memory Address Register stores the address of the data or instructions to be fetched from or sent to.

Front 7

What is the MDR and what does it do?

Back 7

The Memory Data Register stores the data that has been fetched from or stored in memory.

Front 8

What is the CIR and what does it do?

Back 8

The Current Instruction Register is where fetched instructions are copied to for execution.

Front 9

What are buses and what do they do?

Back 9

Buses are circuits on the motherboard that connects the CPU to other components. A bus moves instruction and data around the system.

Front 10

What are data buses and what do they do?

Back 10

They send data to the memory or receive data form the memory. Data can flow both ways along a data bus.

Front 11

What are address buses and what do they do?

Back 11

They send information about where data needs to go by sending an address to the memory. The address bus only sends data in one direction.

Front 12

What are control buses and what do they do?

Back 12

Sends information about where data needs to go by sending an address to the memory. The address bus only sends data in one direction - from the CPU to the RAM.

Front 13

Describe the Fetch-Decode-Execute Cycle.

Back 13

Fetch:

1. Load the address in the PC to the MAR.

2. Increment PC

3. Load instruction given by MAR into MDR

4. Load instruction in MDR into CIR

Decode:

5. Decode instruction in CIR

Execute:

6. Execute instruction

Front 14

How does clock speed affect CPU performance?

Back 14

During a clock cycle the processor can fetch, decode, and execute a simple instruction. A bigger clock speed means more cycles per second, so more instructions executed per second.

Front 15

How does the number of cores affect CPU performance?

Back 15

CPUs with multiple cores can execute multiple instructions at the same time.

Front 16

How does cache affect CPU performance.

Back 16

Cache is an area of very fast memory that links the CPU with main memory. It temporarily stores data and instructions the CPU is likely to need imminently or more than once.

More cache means more instructions can be stored. Faster cache means the instructions can be read quicker.

Front 17

How is pipelining used in a processor to improve efficiency?

Back 17

Several instructions are partially executed at the same time.

Front 18

What is von Neumann architecture?

Back 18

A single control unit sequentially works through instructions.

Data and instructions are stored in memory together and sent along the data bus.

Front 19

What are the advantages of von Neumann architecture?

Back 19

Flexibility. Instructions and data can occupy the same memory so you don't have to think ahead of time as to how you want to split the memory.

Front 20

What are the disadvantages of von Neumann architecture?

Back 20

Two memory accesses need to be made so it is slower.

Front 21

harvard architecture?

Back 21

nope

Front 22

What are the features of a RISC CPU?

Back 22

Simpler instructions.
Further away from high level languages.

More efficient at simpler tasks.

Longer code requiring more RAM.

Lower clock speed.

Perform simpler tasks quicker.

Use less power.

Smaller.

Cheaper.

Front 23

What are the features of a CISC CPU?

Back 23

More complex instructions.

Closer to high level languages.

Smaller code requiring less RAM.

Higher clock speed.

Intensive tasks will be better.

Use more power.

Larger.

More expensive.

Front 24

What are GPUs and their uses?

Back 24

A graphics processing unit is specifically designed to perform calculations associated with graphics. Other than rendering graphics, they can be used for:

Modelling physical systems.

Audio processing.

Breaking passwords.

Machine learning.

Front 25

What is a multicore system?

Back 25

Multicore processors can support multithreading.

Front 26

What is a parallel system?

Back 26

Parallel processors can use multiple CPUs to complete more tasks in a certain amount of time. It works by many processors working together to perform a single job, which is split up into tasks.

Front 27

What are advantages of parallel systems?

Back 27

Increased speed

Complex tasks done efficiently

Many instructions at once

Different processors can handle different tasks/parts of the same job

Front 28

What are disadvantages of parallel systems?

Back 28

Not suitable for some programs.

Programs need to be written specially for it.

Operating system is more complex.

More complex OS.

Front 29

What are the properties and uses of magnetic storage devices?

Back 29

Patterns of magnetisation are used to represent binary sequences on magnetisable material.

They have high capacity at a low cost.

Front 30

What are the proportionates and uses of flash storage devices?

Back 30

Flash media works by a special type of ROM that can be overwritten.

It can be read from and written to at high speeds, but are more expensive than optical and magnetic media.

Front 31

What are the proportionates and uses of optical storage devices?

Back 31

Works by using a laser and looking at its reflection, determining where there are pits on a surface representing 1s and 0s.

Optical media tend to be cheap to distribute and fairly resilient.

Front 32

What is RAM?

Back 32

Random access memory. Access to RAM is quicker than a storage device. Programs and data being run by a computer are temporarily stored here. RAM is volatile.

Front 33

What is ROM?

Back 33

Read only memory. Can be read from but not written to. A common use is for storing the program to boot up the computer. ROM is non-volatile.

Front 34

What is virtual storage?

Back 34

Storage area networks can connect numerous different types of storage device can be connected as a single device. Virtual storage will abstract the type of storage device in a SAN.

Front 35

What is the need for, function, and purpose of operating systems?

Back 35

Makes sure all the parts of the computer can work together. Provides user interface. Ensures all errors are reported to users. Manages memory. Provides utility programs.

Front 36

What is paging?

Back 36

Memory can be split up into smaller pages. Pages are a fixed size. Each physical unit is a page.

Front 37

What is segmentation?

Back 37

Memory can be split into its logical parts, segments containing either data or instructions. Segments may be of variable sizes. Divides the virtual address into separate logical segments.

Front 38

What is virtual memory?

Back 38

Use of hard disk as if it were main memory.

Uses paging/fixed size units.

Swap pages between memory and backing store to make space for pages needed.

Holds part of program not in use.

Allows programs to run that need more RAM than available.

Front 39

What is an interrupt?

Back 39

A signal sent to the CPU to inform it that a device/program needs attention.

Front 40

What is the order of priority of interrupts?

Back 40

1. Power failure

2. Software

3. Clock interrupt

4. Peripheral interrupt

Front 41

How do interrupts fit into the FDE cycle?

Back 41

Before the FDE cycle begins, the interrupt register is checked to see if an interrupt has occurred. The program is halted (contents of registers stored in a stack) until the interrupt has been serviced then it continues.

Front 42

What is scheduling?

Back 42

How and when a process is swapped in and out of the CPU, thus enabling apparent multitasking.

Front 43

What is the purpose of scheduling?

Back 43

Make efficient use of processor time/resources

Provide no apparent delay for users

Maximise number of jobs processed

Front 44

Describe round robin scheduling.

Back 44

Each user allocated time slice. When time is up, moves to next user. Repeats until all users serviced.

Front 45

Describe first come first serve scheduling.

Back 45

First process to arrive is dealt with by CPU. Other processes are queued up in order.

Front 46

Describe multi-level feedback scheduling.

Back 46

Multiple queues used. Each queue has different priority. Queues based on the need for the processor. Give preference to short jobs and I/O bound processes.

Front 47

Describe shortest job scheduling.

Back 47

Processes added to queue in order of the time needed for each job in ascending order. Process is run until it finishes.

Front 48

Describe shortest time scheduling.

Back 48

Scheduler estimates how long each process will take. The one that takes the least amount of time is run first. If a shorter job is added then it is switched to.

Front 49

Describe a distributed OS.

Back 49

Independent networked computers combining processing power for a single task across a network. Presented to user as single system.

Front 50

Describe an embedded OS.

Back 50

Dedicated function, low power, low cost, little memory required, limited amount of hardware resources.

Front 51

Describe a multi-tasking OS.

Back 51

Lets multiple programs run at the same time. Programs scheduled so they each get a time slice of processor time.

Front 52

Describe a multi-user OS.

Back 52

Lets more than one user access computer's resources at a time. They share processor time.

Front 53

Describe a real-time OS.

Back 53

Little/no delay between input and computer's response. Executed within a known time frame, high rate of redundancy, processor never at capacity, used in critical environment.

Front 54

Describe a BIOS.

Back 54

Basic input/output system. Runs when PC is switched on. Responsible for detecting (POST), initialising, and testing hardware components as well as booting the OS (boot loader).

Front 55

Describe device drivers.

Back 55

Software that tells OS how to communicate with a device. Handles translation of requests between device and computer. Defines where process must put outgoing data and where incoming data will be stored. Wakes up device when it is needed and puts it to sleep when it is not.

Front 56

What are virtual machines?

Back 56

When software is used to take on the function of a machine, including executing intermediate code or running an operating system within another.

Front 57

What is application software?

Back 57

Software that allows a user to perform a task or produce something.

E.g. word processing, spreadsheets, desktop publishing, presentation, image editors, databases, web browsers, CAD, CAM

Front 58

What is utility software?

Back 58

A small program that has one purpose, usually concerned with the maintenance of the system.

Front 59

What do anti-virus utilities do?

Back 59

Detect and remove viruses.

Front 60

What do disk defragmentation utilities do?

Back 60

Groups all the parts of each file together on the hard disk so they can be read in one go.

Front 61

What do compression utilities do?

Back 61

Reduce the overall size of a file. This speeds up transmission of data.

Front 62

What do file manager utilities do?

Back 62

Enables the user to do simple file manipulation.

Front 63

What do backup utilities do?

Back 63

Automatically makes copies of file to prevent loss of data. It may put backups on different hardware devices at regular intervals. Incremental backups are made.

Front 64

What is open-source software?

Back 64

Software distributed with the source code. It can be shared and modified by users who can modify it to their needs. Anyone can have a part in the development of the software.

Front 65

What is closed-source software?

Back 65

Software that cannot be decompiled.

Front 66

What is a translator?

Back 66

They convert source code from assembly language or high-level code to object code and detect errors in source code.

Front 67

What are interpreters?

Back 67

They translate interpreted languages into machine code one line/statement at a time. It reports one error at a time then stops.

Front 68

What are compilers?

Back 68

They translate the whole program as a unit into machine code before the program is run. They create an executable program. They may report a number of errors at the same time. They optimise the code.

Front 69

What are assemblers?

Back 69

They translate a program from assembly language into machine code. One assembly language instruction is changed into one machine code instruction.

Front 70

What is lexical analysis?

Back 70

When each key word is replaced with its binary token. It will get rid of characters like additional spaces, lines, and tabs. It will delete comments. It will create a look up table for the variables (symbol table) containing the values and locations of variables.

Front 71

What is syntax analysis?

Back 71

When the compiler uses the keyword table to decide what to do with each instruction. It compares what it gets with what its expecting. It will return an error if it doesn't get what it's expecting.

Front 72

What is code generation?

Back 72

When the compiler takes each statement and converts it to low level/intermediate code. Each high level instruction is translated into many low level ones. Code optimisation is then done.

Front 73

What is code optimisation?

Back 73

When unnecessary instructions are removed.

Front 74

What are library routines?

Back 74

Pieces of code for carrying out a process that recurs many times in a larger program. They are loaded into memory by a loader and linked to the necessary parts of the code with the linker.

Front 75

What is a relational database?

Back 75

Keeps data as number of related tables (avoids data duplication and inconsistent data).

Front 76

What is a flat-file database?

Back 76

All records kept on one table. Each row is one record, each column is a different file.

Front 77

What is a primary key?

Back 77

Unique identifier in a table.

Front 78

What is a foreign key?

Back 78

A primary key of one table might be linked to another table, where it appears as a foreign key.

Front 79

What is a secondary key?

Back 79

An additional key which can be used to search for a record in a database. They don't have to be unique.

Front 80

What is entity relationship modelling?

Back 80

The process of drawing up an entity-relationship (ER) diagram that describes relationships between entities (objects that data is being held about).

Front 81

What is indexing?

Back 81

Sequential files can be searched quicker by producing a separate index file. Each category is linked to a position in the file where that category starts.

Front 82

What are characteristics of networks?

Back 82

A network is any number of computers connected together, sharing processing power, storage, and resources.

Front 83

What are protocols?

Back 83

They are a set of rules governing the way that devices communicate with each other.

Front 84

In the TCP/IP stack, describe the application layer.

Back 84

Consists of applications and processes that use the network, the layer the user interacts with.

Front 85

In the TCP/IP stack, describe the transport layer.

Back 85

Provides end-to-end data delivery services. Responsible for delivering data to the appropriate application process to the host computer.

Front 86

In the TCP/IP stack, describe the internet layer.

Back 86

Defines the datagram and routing of data. Adds IP addresses stating where the data is from and where it's going. Responsible for the routing of data.

Front 87

In the TCP/IP stack, describe the network layer.

Back 87

Consists of routines for accessing physical media. The actual hardware components including wires and network interface cards.

Front 88

What is DNS?

Back 88

Domain name system. Converts domain to IP address by contacting a DNS server.

Front 89

What are LANs?

Back 89

Computers linked together over a small geographical area. Peripherals can be shared.

Front 90

What are WANs?

Back 90

Computers connected together over a large geographical area. Each computer has it's own peripherals instead of sharing them.

Front 91

What is packet switching?

Back 91

Data split into fixed sized packets.

Each packet is placed on network individually.

Packets follow most convenient route/path.

Packets re-ordered and re-assembled at destination.

Front 92

What is circuit switching?

Back 92

Data split into fixed sized packets.

A route/path is reserved before transmission.

Each packet follows the same route/path.

Packets sent in order one after the other.

Packets re-assembled but not re-ordered.

Front 93

What is abstraction?

Back 93

The process of separating ideas from particular instructions/reality. It is a means of only using relevant detail.

Front 94

Why use abstraction?

Back 94

It maximises our chance of solving a problem. It helps separate the component parts. It allows us to decide which are worth investigating.

Front 95

What is a variable?

Back 95

A named memory location used to store and manipulate data which can be changed while the program is running.

Front 96

What is a constant?

Back 96

A named memory location whose value cannot be changed while the program is running.

Front 97

What is a sequence?

Back 97

A set of instructions that are executed in the order in which they are written.

Front 98

What is selection?

Back 98

When the program has to decide which instructions to do according to a condition.

Front 99

What is iteration?

Back 99

A set of instructions that are executed a finite number of times or until a condition is met.

Front 100

What are IDEs used for?

Back 100

Highlighting keywords, automatic line numbering, making code easier to read. They also have automatic error checking, error reports, and breakpoints.