OCR A Level Computer Science Paper 1 - Computer Systems
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OCR A Level Computer Science Paper 1 - Computer S
Institution
OCR A Level Computer Science Paper 1 - Computer S
OCR A Level Computer Science Paper 1 - Computer
Systems
OCR A Level Computer Science Paper 1 - Computer
Systems
OCR A Level Computer Science Paper 1 - Computer
Systems
OCR A Level Computer Science Paper 1 - Computer
Systems 2023-2024
PC - ANSWER-Program counter, contains the address of the next
instruction
CIR - ANSWER-Current Instruction Register: stores the address of the next
instruction currently being executed and decoded
MAR - ANSWER-Memory Address Register, holds relevant memory
address (to read from or write to)
MDR - ANSWER-Memory Data Register, stores data being transferred to
and from memory, acts as a buffer
ALU - ANSWER-Arithmetic and Logic Unit, does all mathematical
calculations and makes all logical decisions
Accumulator - ANSWER-A storage register in the ALU that holds data
temporarily while the data is processed and before it is transferred to
memory.
RISC - ANSWER-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 - ANSWER-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 - ANSWER-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 - ANSWER-A CPU with more than one core on the same
chip - makes use of parallel processing for optimum efficiency
, OCR A Level Computer Science Paper 1 - Computer
Systems 2023-2024
What affects processor performance? - ANSWER-- 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 - ANSWER-Random Access Memory - stores programs and data
currently in use. Volatile
ROM - ANSWER-Read Only Memory - holds information which must be
permanently in memory eg. BIOS
What are the functions of an operating system? - ANSWER-- 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? - ANSWER-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? - ANSWER-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? - ANSWER-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? - ANSWER-An OS which allows
each user to run more than one job at a time.
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