Exam (elaborations)
OCR Computer Science A level paper 1
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OCR Computer Science A level paper 1 OCR Computer Science A level paper 1 OCR Computer Science A level paper 1
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OCR Computer Science A level paper 1PC - CORRECT ANS Program counter, contains the address of the next instruction
CIR - CORRECT ANS Current Instruction Register: stores the address of the next instruction currently
being executed and decoded
MAR - CORRECT ANS Memory Address Register, holds relevant memory address (to read from or write
to)
MDR - CORRECT ANS Memory Data Register, stores data being transferred to and from memory, acts as
a buffer
ALU - CORRECT ANS Arithmetic and Logic Unit, does all mathematical calculations and makes all logical
decisions
Accumulator - CORRECT ANS A storage register in the ALU that holds data temporarily while the data is
processed and before it is transferred to memory.
RISC - CORRECT ANS Reduced Instruction Set Computer: Only simple instructions taking one clock cycle
are executed - currently more widely used than CISC
Advantages: allows for pipelining, execution will be quicker or as fast as CISC
Disadvantages: Compiler has to do more work, more RAM required
CISC - CORRECT ANS Complex Instruction Set Computer: Large instruction set is used to minimise lines of
code required - mainly used for microcontrollers and embedded systems
Advantages: compiler has very little work to do, not much RAM required
,Disadvantages: Building in specialised instructions can be inefficient when only ~20% get used per
program
GPU - CORRECT ANS Graphics Processing Unit - dedicated graphics processor on a graphics card, used to
render images stored in the RAM of the graphics card.
Multi-core CPU - CORRECT ANS A CPU with more than one core on the same chip - makes use of parallel
processing for optimum efficiency
What affects processor performance? - CORRECT ANS - The number of processor cores: more cores ->
better performance
- The processor's clock speed: faster clock speed -> better performance
- Amount/type of cache memory: more/better cache memory -> better performance
RAM - CORRECT ANS Random Access Memory - stores programs and data currently in use. Volatile
ROM - CORRECT ANS Read Only Memory - holds information which must be permanently in memory eg.
BIOS
What are the functions of an operating system? - CORRECT ANS - Providing a user interface
- Memory management
- Interrupt service routines
- Processor scheduling
- Backing store management
- Input and output management
, What are the types of memory management? - CORRECT ANS Paging: Available memory is divided into
fixed size pages, process in memory can be held in non-contiguous pages, mapped to logical addresses
by a page table
Segmentation: Divides address space logically into segments of varying length
What is virtual memory? - CORRECT ANS A technique that uses a portion of the computer's hard disk as
an extension of RAM - swaps files in and out of RAM by a process called disk thrashing
What is a distributed operating system? - CORRECT ANS Form of parallel processing system which splits
tasks over multiple computers - OS coordinates so that the system appears to the user as a single system
What is a multitasking operating system? - CORRECT ANS An OS which allows each user to run more
than one job at a time.
What is a multi-user operating system? - CORRECT ANS Allows multiple users to use a computer system
by allocating each one a slice of processor time - uses a scheduling algorithm
What does a mobile operating system comprise of? - CORRECT ANS Mobile OSes are made up of two
separate operating systems:
A main system operating the user interface/application software
A low-level real-time operating system which is hardware-specific
What is an embedded operating system? - CORRECT ANS An OS on a chip instead of on a hard drive,
designed to do simple things adapted for specific hardware/functions
What is a real-time operating system - CORRECT ANS Processes data as it comes in - in real time
Open Source Software - CORRECT ANS Program code made publicly available for free; it can be copied,
distributed, or changed without the stringent copyright protections of proprietary software products.
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