Computers Flashcards
What are the components of the CPU?
- Control Unit (CU)
- Decoder
- Clock
- Cache
- Registers
- Buses
- Arithmetic Logic Unit (ALU)
What is the main function of the CPU?
Fetch-Decode-Execute cycle
What does the CU do?
- Controls all other components
- Contains the decoder
What does the decoder do?
Interprets instructions and tell ALU what operations to carry out
What does the clock do?
Controls the rate at which program instructions are carried out (cycles)
What is cache?
Very fast RAM
What do the registers do?
- Memory locations
- Some perform special functions in the FDE cycle
What do the buses do?
Carry electrical signals between:
- components in the CPU
AND
- the CPU and other components on the motherboard
What does the ALU do?
Performs arithmetic and logical operations
What registers are used in the FDE cycle? What do they do?
PAMM
- Program Counter: holds the address of the next instruction to be fetched
- Accumulator: stores the result of calculations done by the CPU
- Memory Data Register (MDR): a temporary store (buffer) for anything copied from memory
- Memory Address Register (MAR): holds the address of the memory locations currently being read (fetched) or written to
What happens during the fetch process?
- the CU sends a ‘read’ signal to the RAM on the CONTROL BUS
- uses the ADDRESS BUS to send signals, specifying the required memory location in the RAM
- contents are transferred TO the CPU along the DATA BUS
- the CONTROL BUS manages the information flow between components
What buses are used during the fetch?
(CAD C)
- Control Bus
- Address Bus
- Data Bus
- Control Bus
What is cache memory?
- Very fast memory (usually within the processor itself)
- Speeds up processing by storing recently or frequently used instructions so they don’t have to be fetched from main memory (which is much slower)
- As cache becomes larger, it becomes harder to find data so is slower so cache is split into different levels
- Too expensive to replace RAM in personal computers
Why is secondary storage needed?
- Stores programs and data PERMANENTLY
- Used to transfer stored data between computers
Average size of magnetic storage capacity?
1 terabyte
How is the data encoded in magnetic storage?
Encoded as opposing magnetic polarities on the surface of the disc by electromagnets in the read-write heads
How is magnetic storage read?
The discs spin and read-write heads move across the disc
How is digital data stored in optical storage?
By etching pits onto the surface of the disc
How is optical storage read?
When the light from a laser hits the:
- LANDS it is reflected back to a detector (1)
BUT
- PITS scatter the light away so no light is detected (0)
What is solid-state memory?
NAND flash memory
How is data stored in solid-state memory?
- Consists of floating gate transistors (that don’t lose their state when power is switched off)
- At first all transistors are charged (set to 1)
- When a save operation begins, current is blocked to some transistors (setting them to 0)
What makes up an embedded system?
- Processor
- Memory
- Input and Output Interfaces
What does the OS do?
- Manages users’ interactions through the user interface
- Manages peripheral devices
- Controls computing processes
- Allocates CPU and memory resources
What is utility software?
Set of tools that can be used to analyse and optimise efficiency
What is application software?
An END-USER PROGRAM:
- perform user-identified tasks e.g, word processing or photo editing
What are the types of user interface?
- CLI (Command Line Interface): user types in commands
- GUI (Graphical User Interface): Windows, Icons, Menus, Pointers (WIMP)
- Menu interface: provides menus to go through
Why are usernames and passwords used?
- To allocate permissions for access to files and folders
- Authentication
What are drivers?
- Control ALL peripherals
- Carry out necessary translations to allow the CPU and devices to communicate properly
What is encryption?
Scrambling of data into a form that cannot be understood by unauthorised users
Why is encryption used?
To protect data from unauthorised users
What is an incremental backup?
Only new or changed data are backed up to save time
What is a full backup?
All of the data is backed up
What is malware?
Software that has been designed to gain unauthorised access to a computer system in order to disrupt its functioning or collect information
What is a virus?
- A computer program hidden inside another program
- Usually has a harmful effect e.g corrupting or deleting data on a disc
- It can replicate itself and insert itself into other programs or files which can be passed on
What is spyware?
- Often comes packaged with other free software and the user does not know they’ve installed it
- Spies on users by sending screenshots and key presses to the hacker’s computer (revealing details of passwords)
What is anti-virus software?
- Should check all files that are loaded onto a computer for viruses
- Can be set to carry out routine scans and should be set to check for viruses in emails
What is anti-spyware software?
Checks for and blocks spyware
What is file repair?
Type of data recovery software that can repair corrupted files
What is file conversion software?
Software that can convert one type of file format into another so that it can be used by another program
What is a computer model?
Attempts to abstract the rules and mechanisms that control real-life systems and apply them in computer programs so that they can be used to SIMULATE the behaviour of those systems under different conditions
What would we used computer models for?
- Flight simulators
- Weather forecasting
- Traffic flow
- Financial modelling
Advantages of using computer models
- Safety: ability to experiment without harming people or the environment
- Financial: new products can be tested without having to build prototypes
- Repetition: tests can be quickly repeated to ensure similar outcomes
- Adjustments: changes to the rules and input data can be made quickly to see the outcomes
Disadvantages of using computer models
- The mathematical calculations may be too complex to model real-life situations
- May be difficult to identify all the rules correctly
- The models is not reality so the answers might be different to reality
- The processing power needed to run the model may be greater than what is available
What is a low-level language?
- Consists of millions of 1s and 0s
- Little of no abstraction
- Very fast for the processor to carry out
- Hard for humans to read
- e.g. machine code
What is assembly language?
- A low-level language
- Each instruction is directly equivalent to one in machine code
- Mnemonics are used to replace the command represented as strings of 1s and 0s
- e.g. ADD is used to replace the binary command to add two numbers together
What is high-level language?
- Programming languages that resemble human languages
- Use key words such as ‘print’, ‘if’, ‘then’
- Have to be translated into machine code in order to operate
- e.g. Java or Python
What are the uses of low-level languages?
- Often used in the programs used by embedded systems (e.g. cameras, microwaves, TVs) as it can be used to directly control system hardware
- Used to write device drivers and real-time systems where speed is essential
- Assembly language is specific to each type of CPU: programs written for one type CANNOT be used on others
What are the uses of high-level languages?
- Most software is written in high-level languages
- Less time consuming to write and quicker to test
- Programs are portable from one machine to another
- Most high-level languages can be used with different types of CPU
What are the three types of translators?
- Compiler
- Interpreter
- Assembler
What does a compiler do?
Translates the source code into a standalone, machine code program that can then be executed by the processor
PROS of compilers?
- The translation is done once only and as a separate process
- The program that is run is already translated into machine code so it can be executed more rapidly
- Protects the software from competitors who would otherwise be able to see the source code
CONS of compilers?
- If it encounters any errors, it carries on trying to compile the program and reports the errors at the end
- You cannot change the program without going back to the original source code, editing that and RE-COMPILING
What does an interpreter do?
- Translates the high-level code line by line into machine code
- It is needed each time the program is run
PROS of interpreters?
- When an error is found, the interpreter reports it and stops and pinpoints the error to that the programmer knows where it has occurred
- The code is NOT platform specific and can be run on different operating systems and platforms as long as there is an interpreter
- The program can easily be editing as it always exists as source code
CON of interpreters?
- Every line has to be translated every time it is executed SO is slower
What do assemblers do?
- Translate the mnemonics of assembly language into machine code instructions
