U1 - CPU
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WHAT ARE TRANSISTORS ?
Tiny switches that control the flow or current. Current represent 1 and no current 0
WHAT ARE TRANSISTORS STORED ON ?
Slices of silicon A single chip can contain thousands of transistors
DESCRIBE F-D-E USING VON NEUMANN ARCHITECTURE
Data from currently running instructions are stored in binary in the main memory Instructions are fetched from the memory into the CPU one at a time The instruction is decoded and run The next instruction is fetched from memory Data is fetched as and when needed
WHAT IS VON NEUMANN ARCHITECTURE ?
The design on which general purpose computers are based
NAME 5 REGISTERS
Program Counter Memory Address Register Memory Data Register Current Instruction Register Accumulator
WHAT IS A REGISTER ?
A fast access temporary storage location in the CPU
WHAT DOES A PC DO ?
Program Counter Keeps track of the memory ADDRESS of the NEXT instruction
WHAT DOES THE MAR DO ?
Memory Address Register Holds the ADDRESS of the instruction CURRENT instruction
WHAT DOES THE CIR DO ?
Current Instruction Register TEMPORARY holding area for the INSTRUCTION that is being decoded
WHAT DOES THE MDR DO ?
Memory Data Register TEMPORARILY stores data that has been fetched from memory
WHAT DOES THE ACCUMULATOR DO ?
Register in ALU that holds the RESULTS of currently running instructions
NAME THE 4 CPU COMPONENTS
Registers Control Unit ALU Memory
CONTROL UNIT
Directs the flow of data Coordinates all parts of the CPU Controls clock
ALU
Arithmetic Logic Unit Performs all calculations and logical operations within the CPU
NAME 3 BUSES
Address Bus Data Bus Control Bus
WHAT DOES THE ADDRESS BUS DO ?
When data is saved or loaded from memory, the address it is stored at must be sent Memory address travel on the address bus GOES BETWEEN INTERNAL MEMORY AND RAM
WHAT DOES THE DATA BUS DO ?
When data is sent between different parts of the computer it is sent on the data bus
WHAT DOES THE CONTROL BUS ?
The CU uses this bus to send control signals to different parts of the computer
FETCH
The CPU reads the PC to locate the address of the instruction. The PC value is COPIED TO THE MAR and sent on the address bus. The CU tells the RAM to check the A-Bus and send the INSTRUCTION at that location on the DATA BUS to the MDR
DECODE
The CU AUTHENTICATES THE INSTRUCTION in the CIR. The instruction is decoded to determine the ACTION THAT NEEDS TO BE CARRIED OUT
EXECUTE
SIGNALS ARE sent to different parts of the CPU to execute the instruction. Sent via the CONTROL BUS. Any arithmetic or logic functions are performed in the ALU
WHAT 3 FACTORS AFFECT PERFORMANCE ?
CACHE CLOCK SPEED CORES
WHAT DOES CACHE DO ?
Holds frequently used instructions Improves performance as more cache means more frequently used instructions available quicker Increase hit rate INCREDIBLY FAST BUT VOLATILE AND EXPENSIVE MEMORY used in the CPU
CLOCK SPEED
Number of F-D-E cycles a CPU can run per second FASTER CLOCK SPEED = MORE INSTRUCTIONS EXECUTED Measured in Hertz OVERCLOCKING can strain battery and requires a cooling system