Computer Systems Flashcards
What does an OR gate look like?
What does a NOT gate look like?
What does an AND gate look like?
What does a XOR gate look like
How do you represent NOT(A)? What is another word for the NOT gate
Ā, negation
How do you represent (A OR B), what is another word for the OR gate?
(A + B), Disjunction.
How do you represent (A AND B)? What is another word for the AND gate?
(A.B) , Conjunction
How do you represent (A XOR B)? What is another word for XOD gate?
(A ⊕ B), Exclusive disjunction
What does XOR gate do?
returns true only if exactly one input is true, otherwise returns false.
What is application software, give examples?
Application software is for user benefit. Word processors, internet browsers, games
What is system software, give examples?
System software performs the tasks needed to operate the hardware and provide services for other software. OS, game engines, utility programmes.
What is the Operating System?
the essential software that links the hardware and other software together and generally manages the computer system.
What is the purpose of the OS? 4 points.
- It manages the hardware (only the OS can interact with it)
- Manages the applications installed
- Creates a user interface (abstraction from the hardware
- Provides a layer of security (as it sits between the hardware and the application software
What are the two categories of the user interface?
- Command line interface - A shell responding to successive text commands (more direct and compact)
- Graphical User Interface - Uses icons and visual indicators to navigate and issue commands
How does the OS control process management? Multi tasking, single tasking?
- process = programme being executed by the computer
- A single tasking OS executes one process at a time and interrupts it if necessary
- a Multi tasking OS executes 1 process at a time but allows multiple applications to run by rapidly switching between process
- The OS allocates CPU time for each process and prioritises them in order of importance
How does OS control memory management?
- When a user opens a programme it needs to be loaded into the RAM.
- The OS oversees allocation and management of RAM space
- if there is no space, virtual memory may be used
- Different data and instructions are kept separate for security reasons
How does the OS control peripheral management?
The OS uses device drivers which are programmes that convert between the peripheral signals and the OS signals
How does the OS control user management and file management
- Manages usernames/passwords and account creation
- There are user account controls
- Maintains records of all the files stored in secondary storage, and what user can access what. (file permissions)
What are examples of low level languages?
- Machine code, simplest can be directly run by the processor. Machine code is specific to the processor, high level code can run on any computer with the right translator
- Assembly code
What are examples of high level languages?
Python, Pseudocode
What types of languages are portable? Are they slower or faster to implement?
High level languages, can run on any computer. More abstract languages leave more work to be done during runtime so are much slower to execute.
What is an assembler?
Assemblers are used to translate a program written in a low-level assembly language into a machine code (object code) file so it can be used and executed by the computer.
What is a compiler?
Compilers are used to translate a program written in a high-level language into machine code (object code). Once compiled (all in one go), it can be directly executed by the computer.
- You can distribute your programs without the source code, as it is no longer needed
- Error messages are only shown after scanning the whole code
What is an interpreter?
- High level to machine code.
- Works line by line, translates aline then immediately execute it
- Every time you want to execute a code you have to translate it again.
- Needs the source code and interpreter at all times
- Slower than compiler
What is Main Memory?
Any memory that is directly accessible by the CPU: RAM, ROM and (sometimes) Cache
What is volatile memory?
memory that loses its data when power is lost. RAM, Cache. Volatile memory is faster
What is non-volatile memory?
retains its data when power is lost. ROM, Hard-disks
Is memory volatile or non-volatile? Is storage volatile or non-volatile?
Memory - volatile
Storage - non-volatile
What is RAM?
- Random access memory, Volatile
- Reading data from RAM takes same time regardless of where it is physically stored on the disk
- RAM is very quick, stores a copy of open programmes and OS data currently in use, as it is directly accessed by the CPU
What is ROM?
- Read only memory, Non-volatile
- Can only be read, can’t be changed once programmed
- Used in small amounts to store essential programmes like bootstrapping programmes
What is Cache?
- A type of memory that stores copies of frequently accessed data
- Much faster than RAM, but has lower capacity
- Sits in between the processor and the RAM, and is checked for the data before the RAM
What is optical storage?
- Stores the data as variations of heights on the disks surface.
- To read the data, the light is shined on the disk, light that hits a land reflects different to when it hits a pit
- Data is written with a laser burning pits in to the disk
Pros and Cons of optical storage.
- Fairly reliable + durable
- Good portability
- Can be easily damaged (scratches)
- Small capacity
What is magnetic storage? (Hard drives)
- Uses read write heads that contain electro magnets
- Part of the disk is magnetised or demagnetised
- Magnetised (1) Demagnetised (0)
Pros and Cons of magnetic storage.
- Large capacity
- Cheap
- Reliable
- Not durable
- Not portable
- Can be noisy and generate heat.
What is solid state storage?
- Form of flash memory (non mechanical)
- Digital circuits to retain data
Pros and Cons of solid state storage?
- Very fast
- Very reliable as non mechanical
- Don’t need defragmentation
- Silent
- Smaller capacity than magnetic
- Expensive
What is cloud storage?
- Data is stored on multiple servers in a remote location, servers use magnetic (or even SSS)
- Generally operates through a web based API
Pros and Cons of cloud storage.
- Durable, multiple copies are often kept
- Reliable, service may not be reliable
- Portable, can be accessed anywhere
- May be cheaper for large companies
- More expensive for smaller users
