OCR Computer Science
- Created by: wafflypig
- Created on: 16-04-16 13:17
Define the term computer system
A collection of hardware and software working together to produce a coded solution
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What 3 things must a computer system be able to do?
Input, process and output
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Give 3 examples of an input device
Touchscreen, keyboard, mouse, microphone, footmouse, webcam
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Give an example of a processing device
Sound cards, graphics cards
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Give 3 examples of an output device
Printer, speaker, monitor, plotter
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What are 3 points as to why computer systems are important in the modern world?
Communicate and work with people worldwide. Save lives (eg 999 system). Improve quality of life (eg bionics). Allow secure data access. Better manufacturing
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In computing, what is meant by reliability?
How dependable a computer system is to carry out a job you have entrusted it with
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What is a general purpose computer system?
A computer system that can load and operate with various apps. E.g a laptop/desktop
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What is a dedicated computer system?
Specially produced system that have one purpose. E.g. ticket vending machine
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What is a control computer system?
Computer systems that control machinery. Their output is read by another machine, rather than a human
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What is an embedded system?
Computer system that are part of a larger system
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Give 2 examples of an embedded computer system
Digital watches, satnavs, cameras, MP3 players, traffic lights and controllers of machinery
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What is an expert computer system?
Computer systems that are designed to behave like human experts in a particular field
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What is a management system?
A computer system that brings together information from different parts of a company for human managers to make an informed decision
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Why must computer system be reliable?
So it has the ability to save lives. It could be the difference between life an death. E.g. ATC and medical situations
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Define data integrity
Data being accurate and consistent throughout its life and reflecting what it means in the real world
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How can data integrity be compromised?
Human error, viruses, bugs in code, hardware malfunctions and natural disasters
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Give 2 reasons why software often has errors after being released
Software is complex, testing is expensive, testing is time consuming
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What are de facto standards?
They ensure some things are the same across computer systems so they can be used by everyone. E.g. QWERTY keyboards
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What are de jure standards?
Standards that must be adhered to BY LAW. They are universally accepted. E.g. ASCII and PDF
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What are proprietary standards?
They are decided by the company and ensure all their products work seamlessly together
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What are industry standards?
Standards set by recognised non-commercial organisation E.g. ANSI
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What are open standards?
Not dominated by any one particular group and are produced collaboratively so they can be used across many apps and pieces of hardware
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Give 2 examples of open standards
HTML, HTTP, WAP, SQL
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Give 3 ways energy can be saved in a computer system
Automatic standby, solid state storage (doesn't rotate), modern screens that are more efficient
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Why can computers be bad for the environment?
Contain toxins (cadmium etc), need electricity to run which usually means fossil fuels have been burned.
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Give 3 points of the Data Protection Act
Not transfer data outside the EU, allow people to access data for no more than £10, correct information when requested, adequate protection must be in place
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What is the ALU?
Arithmetic and Logic Unit of the CPU. It does the mathematical aspects of the F-D-E cycle
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Which is the basic architecture that all computer systems use?
von Nuemann
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Where are data and instructions stored, and how?
RAM, as binary numbers
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What is the control unit?
It uses electrical signals to control the flow data through the CPU
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Define the CPU
The Central Processing Unit is the main hardware within a computer whose purpose is to process data
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What cycle does the CPU use?
Fetch - decode - execute
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What is determined by the CPU clock speed?
The speed of the F-D-E cycle. It is measured in cycles per second (Hz). It is usually measured in GHz (billion of Hz)
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What is the boot sequence?
A pattern of processes that contain all the information needed to get the computer up and running.
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Define internet
An international network of computers
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What is cache memory?
Memory that is quickly and easily accessed by the CPU.
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What is the advantage of having multiple processing cores?
More data is processed simultaneously
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What is the disadvantage of having multiple processing cores?
A more complicated operating system is required
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Is RAM volatile?
Yes
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What is meant by volatile memory?
It is lost when the computer is switched off
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Which is bigger, RAM or ROM?
RAM
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Give 2 things stored in RAM
The OS and data currently in use
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Give 1 thing stored in ROM
The boot sequence
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What is virtual memory?
Part of the hard drive that is an extension to RAM
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When you add more RAM, what happens to the amount of virtual memory?
Goes down and the performance of the computer increases
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What is flash memory?
A type of ROM that can be rewritten. It can be portable
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What does a not logic gate do?
Changes the input to the opposite
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To get a high output in an and gate, how many inputs must be high?
2 (both). It must be 1 1. 0 0 will produce an output of 0
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How many inputs must be high for a high output in an or gate?
1 or both.
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What is magnetic memory?
Memory that uses a magnetised field and possibly polarized elemental ions
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Give 3 advantages of a magnetic hard disk
Reliable, high capacity, low cost
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Give 4 main considerations when selecting a type of storage
Capacity, speed, portability, durability, reliability
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What is secondary storage?
Memory used to store data after the computer has been switched off
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Define input device
Passes a control signal into a computer
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Define output device
Presents a processed control signal from a computing device
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What is primary storage?
Volatile memory - includes RAM
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What does system software control?
Hardware
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What dose application software do?
Handles real jobs that users want to do
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What is utility software?
Limited functionality but is used maintain a computer system.
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What is a user interface?
The boundary between the user and machine
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Give an example of a user interface
Command Line, LX Terminal
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What is a GUI?
A graphical user interface is easy to understand and uses recognisable icons
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How are subtitles generated on TV?
Using speech recognition software
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What 2 things does an OS have to do with memory?
Ensure important things are not overwritten and memory is used efficiently
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What is virtual memory used for?
When excess jobs (jobs that won't fit in the main memory) are held in virtual memory
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Give 3 jobs of an operating system
Issues error messages, manages memory, maintains security and access rights of specific users, deals with errors, deals with user inputs
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What is the purpose of defragmentation?
Tidy up the disk so that pointers can send the OS in the right direction, towards the next segment or block, quickly
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What is multiprogramming?
When a system has several programs loaded into memory at the same time. This is very common
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What file type has the extension, .exe
An executable program
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What file type has the extension, .jpg
A compressed image
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What file type has the extension, .xls
Excel
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What file type has the extension, .html
HyperText Markup Language - a website
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What is a file system?
A mostly hierarchical system implemented by the OS to organise files in secondary storag
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What are viruses?
Often attached to legitimate programs, they infiltrate your computer and replicate themselves
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Give 2 things that a virus can do
Damage files, take control of a computer, retrieve confidential data
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Give 3 examples of user privileges on a file
Read, write and run
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What is encryption of a file?
Files are stored in a way that is not understandable to anyone else other than the person with the password (which will decode the file)
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How can a user be authenticated?
With a password, finger print, facial recognition, retinal scanning etc
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What are applications?
Programs that people use to do real world jobs
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Give 3 examples of applications
Autopilots, word processors, MP3 players, games, hotel booking system, traffic light system
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Which ways does utility software in the OS aid security?
Antivirus, spyware protection, firewalls
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Which ways does utility software in the OS aid efficiency?
Auto-updating, clean-up tools, diagnosis, system maintenance, disk organisation (fragnmenter)
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What is custom written software?
Software specially written for a particular customer. It is bespoke
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Give 2 advantages of custom written software
Exact features, developer can be contacted to resolve issues, does not require any special adaptations
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Give 2 disadvantages of custom written software
May not have had extensive testing, expensive, takes long to develop
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What is off-the-shelf software?
Can be bought, boxed, off the shelf and installed
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Give an example of OTS software
MS Office
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Give 2 advantages of off the shelf software
Ready immediately, probably has been well tested, many users = many solutions to issues, lower cost
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Give 2 disadvantages of off the shelf software
Won't be exactly what was needed, may need customisation, might need training
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What is open source software?
Software that is in the public domain for use to gain and develop knowledge
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Give an example of open source software
Linux, Firefox, Libre Office, Apache
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Give 2 advantages of open source software
May be free, can be altered (source code available), extremely reliable (many people will work to improve it)
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Give 2 disadvantages of open source software
No maintenance of contracts, no contacts for issues, irregular updates
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What is proprietary software?
Software that is developed by a company, for profit
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Give 2 advantages of proprietary software
Easy to contact, should have been well tested, regular updates
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Give 2 disadvantages of proprietary software
Expensive, inflexible to needs and there are some deliberate incompatibilities
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What base is binary?
2
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What base is hexadecimal?
16
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What is each digit of binary called?
Bit
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What is 4 bits called?
Nibble
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What is 2 nibbles called?
Byte
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What base is denary?
10
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How many bytes in a kilobyte?
1024
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How many MB in a GB?
1024
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How many KB in a MB?
1024
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What are the powers of 2 up to 128?
1 2 4 8 16 32 64 128
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What denary number is A in hexadecimal?
10
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What is the highest hex value?
F (denary = 15)
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How do you convert from hex to binary?
Convert hex - denary - binary
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What is ASCII short for?
American Standard Code for Information Interchange
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How many characters are represented by ASCII?
128 (127 not including 0)
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How are codes for characters stored in ASCII?
Binary
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How are characters sorted in a table of ASCII?
By increasing denary value
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What is a pixel?
One dot in an image
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What determines how many colours does each pixel represents?
The number of bits per pixel (bpp)
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What is colour depth?
The number of bits used to represent a colour
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What is resolution?
The pixels per inch. More pixels per inch = larger file and better quality image
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What is metadata?
Data about data
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What is a bitmapped image?
The dots get bigger and the image gets blurry
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What is a DAC?
Digital to Analogue Converter
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What is a ADC?
Analogue to Digital Converter?
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Give a use of an ADC
To make sound understandable to a computer
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What is sample interval?
The time between samples of sound being taken. (High interval = low sample rate)
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What is sample rate?
The rate of samples of sound being taken
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What size file is needed for sound with a low sample rate?
Smaller
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What happens if there is a low sample rate?
The will be a poor match between sampled and original sound, eg mouths will move without sound
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What is the bit rate?
The amount of space needed to store each second of the sound sample
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What is an operand?
A data part
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What is an operator?
The instruction part
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What is opcode?
Operators in binary
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Which nibble of a byte of binary is usually the operand?
2nd
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What is the accumulator?
A special register in the CPU that stores the results of any calculation
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What is a length check?
Ensuring a certain number of characters have been entered, within a range
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What is a type check?
Ensure data is of the correct type. E.g. not numerals in a surname
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What is a range check?
Must fall between two limits, e.g. DOB over 18
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What is a presence check?
Checks that something has actually been entered
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What is a lookup check?
Ensures entered data matches what is stored on file
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What is a format check?
Checks data has been entered in the right way. E.g. car number plate must be LLNNLLL
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What is check digit?
Must be exactly the same as previously entered data
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What is verification?
Ensuring data has been entered correctly
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What is a database?
A persistent, organised store of data in a computer
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What is a failover?
A piece of hardware that takes back ups of files on a network in case of a natural disaster
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What is data integrity?
Data reflects what it is in reality
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What is validation?
Ensuring data has been entered in the correct way, as accurately as possible
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Give three places that might use a database
School, bank, doctor surgeries, government etc.
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What is a flat file database?
Just rows and columns - just a spreadsheet
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Is a row or column a record?
Row
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What are columns in a flat file database called?
Fields
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What is a hierarchical database?
A database with different tables with each becoming have more closely related records
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What is an entity?
A single thing (person, object etc.) that data can be stored about in a database
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What is the DBMS?
The DataBase Management System is software that looks after the database on a fundamental level
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Give 3 things a DBMS can do
Protect data, create database applications, run queries, data consistency, keep data accurate, add records, delete records
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What is a relational database?
Data is stored in separate tables. The tables are linked so related data can easily be extracted
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How can a DBMS protect data?
Stops unauthorised access and provides a firewall
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What is the boolean data type?
Used when data is only yes/no or true/false
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What is a primary key?
A unique and identifiable part of a record
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What is a report?
A summarised output from a database
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What is a query?
Extracts data from a database
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What is SQL?
Structured Query Language
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What does the AND operator do in SQL?
Checks 2 conditions are true then selects data that matches this
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What is a node?
A device on a network
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What is a LAN?
A Local Area Network
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What are the advantages of LAN?
Nodes can be updated centrally, data sharing is convenient, easy back ups, expensive peripherals can be shared
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What are the disadvantages of LAN?
Network issues will affect all users, maintenance, security issues
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What is a WAN?
Wide Area Network. Often several LANs connected together
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What is a WLAN?
Wireless Local Area Network
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What are network hubs?
Hardware that connect network devices together
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What is a network switch?
Connect different segments of the network together (aka bridges)
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What is a bus topology?
All nodes are connected to each other in series with terminators at each end to absorb excess data and prevent signal reflection
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Advantages of bus network?
Cheap, easy to set up
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Disadvantages of bus?
1 problem on "backbone" ruins it all, data collisons mean it's slow, small distance covered
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What is a ring network?
When data (tokens) passes through each node in the circle
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Advantage of ring?
No data collisions = fast
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Disadvantages of ring?
1 problem in circle ruins it all
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What is a star network?
Each client is connected to a main switch/hub.
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Positives of star?
Robust, few data collisions = fast
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Cons of star network?
Needs expertise management, hard to set up, more hardware/software needed
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What is a peer - to - peer network?
All computers are equal -useful on the internet
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What is a client-to-server network?
Each node has a different job from another
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What does IP stand for?
Internet Protocol
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What is a data packet?
Collections of data forming a message. This is how data is sent around the internet
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How many bits is an IP address?
32
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What is a MAC address?
Media Access Control does not change (IP does). It is used to identify a device on the network
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Give 3 ways a network can be secure
Backups, archives, failover, disaster recovery, authentication, acceptable use policy,
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What 3 things make a good password?
Mix of cases, long, numbers, obscure word
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What is a modem?
Converts analogue signals to digital for the computer to understand
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Which one does a computer understand, digital or analogue?
Digital ONLY
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What does a router do?
Connects networks together.
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What is CSS?
Cascading Style Sheets reduce the complexity of webpages
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What does GIF stand for?
Graphic Interchange Format
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What is stored in an MPEG file?
Video
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Define lossy compression
Reducing the size of the file by removing some of the unneeded data from the file.
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Give three file extensions that use lossy compression
MPEG, JPG and MP3
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What is lossless compression?
It allows file size to be reduced by not storing repeated data. A table is set up and the file is reconstructed
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What is machine code?
Code that is understood by the computer and is in binary
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Is machine code high or low level code?
Low level
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What is high level code?
Easily understood by humans and near to English E.g. Python
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What is assembly language?
A low level language, understood by the computer that
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What is assembly language?
A low level language, understood by the computer that
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What is assembly language?
A low level language, understood by the computer that
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What is assembly language?
A low level language, understood by the computer that
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What is assembly language?
A low level language based around arithmetic and logic.
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What 2 things could be used to translate between high level and machine code?
Compiler or assembler
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What is a selection in an algorithm?
Looking at conditions to see if it meets a criteria. E.g. correct height for a rollercoaster
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What is iteration in an algorithm?
Instructions are repeated until a condition is met
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What is clock speed?
The amount of instructions executed by the CPU per second
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What is a core of a CPU?
A processor within the CPU
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How many instructions can be run at a time in a quadcore CPU?
4
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What is cache?
A type of memory that stores frequently used instructions so they can be accessed quickly
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How does optical memory work?
Holes are burned into a surface and it is recognised when light is not reflected back to the same place (0).
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What is solid state memory?
Memory that has no mechanical moving parts. Instead, it works with logic gates
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How does a computer differentiate between operand and operators in binary?
There is saved sequence called a bit pattern
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What is a logic error?
A bug in the code that causes the program to not work correctly but does not cause the program to crash
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What is the purpose of a hub in a network?
A common connection points between areas of a LAN that forward packets through different ports
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What is the purpose of a bridge in a network?
x
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What is the purpose of a router in a network?
To connect the network to another network (eg Internet) and forward packets
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What is a packet?
A unit of data that travels through a network and uses an IP address
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What is an IP?
An Internet Protocol address that uses a string of numbers to identify a computer on a network, administered by an admin. It is used by your own router to know where to forward packets
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What is a MAC address?
A Media Access Control will never change because it is unique to your machine, it can identify your machine on a network of networks (eg Internet)
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What is data redundancy?
When the same data is held in 2 separate places
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What is the purpose of a switch in a network?
To connect different areas on the network and forward packets (similar to a hub)
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What is a protocol?
A set of rules, dictating how computers communicate
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What is a sequence in coding?
When an action in coding leads to the next action, in a predetermined order
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What is a sequence in coding?
When an action in coding leads to the next action, in a predetermined order
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Other cards in this set
Card 2
Front
What 3 things must a computer system be able to do?
Back
Input, process and output
Card 3
Front
Give 3 examples of an input device
Back
Card 4
Front
Give an example of a processing device
Back
Card 5
Front
Give 3 examples of an output device
Back
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