OCR A Level Computer Science

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1.1.1a: The Arithmetic and Logic Unit; ALU, Control Unit and Registers (Program Counter; PC, Accumulator;ACC, Memory Address Register; MAR, Memory Data Register; MDR, Current Instruction Register; CIR).Buses: data, address and control: how this relates to assembly language programs.

The characteristics of contemporary processors, input, output and storage devices

Keyword	Definition
Accumulator	General purpose register within the ALU which stores the input and/or output of any calculations
Address Bus	Part of the system bus which transmits the memory location of data to be read from or written to. Links the CPU and immediate access store.
Arithmetic Logic Unit	Part of the CPU which processes data by performing logical and arithmetic operations.
Assembly language	low level code where each operation that the CPU will execute is represented by a separate instruction in code
Control Bus	Part of the system control bus which transmits signals which synchronise and trigger how different parts of the computer work together.
Control Unit	Part of the CPU which sends control signals to initiate and syncronise each part of the fetch, decode, execute process
Current Instruction Register	A register inside the control unit which stores the value of the instruction which has just been fetched.
Data Bus	Part of the system bus which carries data and instructions between the CPU and immediate access store
Immediate Access Store	Memory storage locations which can accessed in one clock tick (without any delay)
Memory Address Register	A register used to store the location of memory currently being being read from or written to
Memory Data Register	A register that works as a buffer between the CPU and the immediate access store which stores the data or instruction currently being transferred on the data bus.
Program Counter	Register which stores the address of the next instruction to be executed
Register	Very fast memory located inside a CPU with only enough capacity to store an individual value or instruction.
System Bus	A group of digital connections that work as a common pathway to send binary data between components of a computer

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1.1.1b: The Fetch-Decode-Execute Cycle; including its effects on registers.

Keyword	Definition
Decode	the part of the instruction cycle where the instruction in the CIR is split into an opcode and operand and any additional data is loaded from RAM if required by the current instruction
Execute	the part of the instruction cycle where the ALU carries out the current instruction and saves the result back to RAM or into the ACC
Fetch	the part of the instruction cycle where the next instruction is read from RAM into the CIR
opcode	part of an instruction which determines what to do (e.g. add / subtract)
operand	part of an instruction which specifies what data is required (e.g. what to add / subtract)

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1.1.1c: The factors affecting the performance of the CPU: clock speed, number of cores, cache.

Keyword	Definition
Arithmetic Logic Unit	the part of the CPU which performs logical or arithmetic binary operations on data
Cache	Limited amount of fast storage which can be used to store commonly accessed values or data that is likely to be requested from a slower storage device in the near future.
Central Processing Unit	the part of a computer that fetches, decodes and executes instructions. Consists of registers, ALU and CU
Clock speed	The number of instructions executed per second. Measured in Hertz (Hz).
Control Unit	the part of the CPU which sends signals to trigger and syncronise all other components
Cores	The number of separate processing units which can execute instructions at the same time (concurrently)

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1.1.1d: The use of pipelining in a processor to improve efficiency.

Keyword	Definition
Branch	A type of instruction which changes the address of the next instruction to to be executed to something other than what the PC register currently stores.
Flush	Operation which needs to be performed on a pipeline when a branch instruction takes place. This clears the pipeline and so reduces performance.
Pipelining	A process which improves the performance of a CPU by allowing one instruction to be fetched whilst the previous one is being decoded and the one before that is being executed.

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1.1.1e: Von Neumann, Harvard and contemporary processor architecture.

Keyword	Definition
CISC (Complex InStruction Set)	A type of CPU design that aims to speed up performance by supporting a large number of specialised instructions.
Contemporary Architecture	Modern additions to CPU design which can improve performance or security
Data	Values which can be stored in variables or constants when a program runs.
Harvard	A type of processor architecture where instructions and data are stored in separate address spaces both with separate address busses and data busses.
Instructions	Program code that can be executed when a program runs.
MMX (MultiMedia eXtensions)	An example of contemporary CPU architecture where complex calculations that are frequently used in encoding / decoding multimedia data (e.g. JPG images) can be performed using single specialised instructions.
Processor architecture	A type of processor design which specifies how the CPU is connected to the immediate access store.
RISC (Reduced InStruction Set)	A type of CPU design that aims to simplify the structure of the ALU, CU and by only supporting a basic instruction set in order to reduce power consumption and cost per core.
SIMD (Single Instruction Multiple Data)	An example of contemporary CPU architecture where one instruction performs the same operation on data in multiple locations at the same time
Von Neumann	A type of processor architecture where data and instructions are stored in the same address space so there's only one data bus and one address bus.

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1.1.2a: The differences between and uses of CISC and RISC processors.

Keyword	Definition
Complex Instruction Set Computer (CISC)	Processor architecture that uses a wide range of specialised instructions that may each take multiple clock cycles to execute
Instruction Set	The range of opcodes that a processor supports, each performing a slightly different function
Reduced Instruction Set Computer (RISC)	Processor architecture that uses a limited range of instructions which can each be executed in a single clock tick.

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1.1.2b: GPUs and their uses (including those not related to graphics).

Keyword	Definition
Central Processing Unit (CPU)	General purpose processor which may have a limited number of cores focusing on integer and logical operations
Graphics Processing Unit (GPU)	Highly specialised point processor which has many cores to perform many floating point operations concurrently
High Performance Computing (HPC)	Using specialised hardware on multiple GPUs to solve complex problems such as AI, cryptocurrency mining and analysing massive amounts of data
Parallelisation	GPUs can perform the same operation on multiple pieces of data at the same time (e.g. performing the same operation on each pixel of an image)

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1.1.2c: Multicore and Parallel systems.

Keyword	Definition
Multicore	A way of improving performance by placing multiple compute units within the same processor so that multiple operations can be executed in parallel.
Parallel processing	A way of improving performance by splitting the tasks that need to be executed across multiple physical CPUs.
Single Instruction Multiple Data (SIMD)	Performing the same instruction on a range of data (e.g. multiple variables) at the same time

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1.1.3a: How different input, output and storage devices can be applied to the solution of different problems.

Keyword	Definition
Barcode reader	Input device which can detect and interpret data represented graphically as black and white lines or dots
CCD	type of image sensor which can reproduce high quality digital images
CMOS	type of image sensor which can detect light without consuming much power
Input device	hardware which sends data into a computer (e.g. scanner, webcam, keyboard, mouse)
Output device	hardware which receives data from a computer so that it can be presented to a user (e.g. printer, display, sound card)
Storage device	hardware used to keep a copy of data on a non volatile medium (e.g. magnetic, optical or flash)

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1.1.3b: The uses of magnetic, flash and optical storage devices.

Keyword	Definition
flash storage	type of storage that uses sold state electronic with no moving parts to store 0s and 1s in NAND cells
magnetic storage	type of storage that uses spinning platters to store 0s and 1s on polarised iron particles
non volatile	type of persistent storage where data is preserved when power is switched off
optical storage	type of storage that uses spinning discs to store 0s and 1s on reflective pits and lands
primary storage	fast volatile storage (RAM)
secondary storage	a type of storage that is slower than RAM but is non volatile and has a higher capacity
volatile	type of storage that loses all data when power is switched off

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1.1.3c: RAM and ROM.

Keyword	Definition
Primary storage	immediate access store (RAM)
Random Access Memory (RAM)	Fast, volatile storage used to store data and instructions
Read Only Memory (ROM)	Non volatile permanent storage used to store instructions loaded when the computer boots up
Secondary storage

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1.1.3d: Virtual storage.

Keyword	Definition
Primary storage	Fast, volatile storage (e.g. RAM) with limited capacity
Secondary storage	Slower, non volatile storage (e.g. HDD) with large capacity
Virtual storage	Using secondary storage to extend the capacity of primary storage

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