A series of GCSE OCR computing revision notes laid out in an organised manner and divided by topic and subtopic, introducing a range of exam vocabulary and key concepts from the anatomy of a CPU to defensive design. It includes both Unit 1 and Unit 2 theory. Also features relevant exam questions on...
1.1 SYSTEMS ARCHITECTURE
KEY CONCEPTS CPU CENTRAL PRO
Computer systems take data (input), process it and then output it.
Embedded systems are computers built in to other devices like washing machines.
They are dedicated to a single task so they are efficient
Clock speed: the number of instructions a processor can carry out per/second. Higher
clock speed = faster CPU.
Number of Cores: The more cores a CPU has the more instructions it can carry out at
once (multitasking). More cores = faster processing.
Cache size: A larger cache gives the CPU faster access to more data
FETCH – DECODE – EXECUTE CYCLE
CPU fetches instruction from the RAM
(Copies memory address to MAR, copies
Instruction to MDR & adds 1 to PC. FETCH
CU decodes the instruction from
the MDR Instruction is executed by
the CU . The next instructions is
CONTROL UNIT (CU): executes instructions and controls the
EXECUTE DECODE
fetched and The cycle repeats.
PROGRAM COUNTER: holds the memory address for the ins
EXAM QUESTIONS ARITHMETIC LOGIC UNIT (ALU): does all of the calculations
, 1.2 AND 1.3 MEMORY AND STORAGE
RANDOM ACCESS MEMORY STORAG
RAM is the computer’s main memory that holds the data, programs and files while they are
being used. SOME STORAGE METHODS SUCH AS A HDD OR SSD HA
OTHER DEVICES SUCH AS CDS AND SD CARDS HAVE SM
RAM is volatile (power off = the data is lost) SHOWN BELOW:
The CPU will fetch instructions from the RAM in the fetch – decode – execute cycle.
When the RAM is full the computer uses VIRTUAL MEMORY. It uses the secondary storage as
temporary RAM so that the computer can continue running (but slowly).
READ ONLY MEMORY
The ROM is on a chip build into the motherboard
It contains the BIOS (boot up sequence for the computer)
ROM is non-volatile (data still stored after power is off)
TYPES OF STORAGE
Secondary Storage: where all data including the programs
are stored when they are not being used
STORAGE KEY INFORMATION
1000 INSTEAD OF 1024 COULD BE USED WHEN DOING
HARD DISK DRIVE (HDD) Magnetic, has moving parts, large capacity, lower cost than BE ALLOWED A CALCULATOR IN YOUR EXAM.
SSD
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