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DAVJ277 1.1

J277 GCSE CS 1.1 Systems Architechture

QuestionAnswer
Central processing unit (CPU) What is its purpose? What tasks does it carry out? Carries out the processing of the computer. Tasks: Fetches data/instructions from RAM, Decodes and executes instructions. Performs fetch execute cycle. Performs calculations/logical operations
What are the features of Von Neumann Architecture? Follows the fetch-decode-execute cycle (instructions decoded one at a time) Instructions and data are held together in the same memory .
What is the Memory Address Register (MAR)? A register in the CPU. Holds the memory address where the next data/instruction will be fetched from or written to
What is the Memory Data Register (MDR)? A register in the CPU. Holds the data/instruction fetched from or to be written to the memory.
What is the Program counter (PC)? A register in the CPU. Holds the address of the next instruction to be run. Between instructions, the contents are incremented (one is added)
What is the Accumulator (ACC)? A register in the CPU. Holds the results of calculations or other processes.
What is a register? Registers are memory locations within the processor. They work at extremely fast speeds.
Name four registers in the Von Neumann Architecture MAR (Memory Address Register), MDR (Memory Data Register), ACC (Accumulator) and PC (program counter)
What is the Arithmetic logic unit (ALU)? A component of the CPU. Carries out calculations and logical decisions. Performs arithmetic operations (+ - * /) Performs relational operations (< > =) Performs logical comparisons e.g. IF x > 3 in the CPU.
What is the Control unit? (CU) What is its purpose? Control unit is a Component of CPU Decodes instructions Provides timing signals and control signals to coordinate how data moves around the CPU in the fetch/execute cycle. Runs the fetch execute cycle
What are the steps of the von Neumann fetch, decode, execute cycle PC is incremented Address of instruction to be fetched is placed in the MAR Instruction fetched from memory Fetched instruction transferred to MDR Instruction is decoded Decoded instruction is executed Process is repeated
What is cache? Memory stored in the CPU providing fast access (as nearer to CPU) to frequently used instructions and data. Cache memory stores copies of data or instructions from RAM that are frequently accessed —more cache = better performance as less time spent accessing RAM
What are the Factors affecting the performance of the CPU? 1) Clock speed—Number of fetch execute cycles per second, measured in HZ. 2) Number of cores—Cores are independent processors within CPU 3) Cache size—faster than RAM, built into CPU
What are the benefits of having more cores? Tasks can be split between processors —...meaning tasks can be processed faster … more processes completed per second 2) Allows multitasking—Run more than one task/instruction at a time … more processes completed per second
Why does more cores not always improve performance? 1) Some software is designed to run on one core so won’t use the extra cores —...depends on the tasks … some cannot be split across cores (if they are dependent on one another) 2) Other factors affect performance—clock speed, cache size, size of ram
What is meant by a clock speed of 3.8GHz? This is the number of fetch/decode/execute cycles run per second 3.8 billion cycles/instructions ….per second
Define an embedded system? A computer system within another device. Has a dedicated function (not general purpose computer)
Give examples of embedded systems Example 1: Washing machine/dishwasher Example 2: Automatic lights Example 3: Sat Nav
What are the characteristics of an embedded system? Often require additional hardware essential to its purpose. For example: Input devices such as sensors and buttons Output devices such as actuators/monitors/speakers Embedded systems often have firmware rather than general purpose operating systems.
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