Structure And Role Of The Processor

Structure And Role Of The Processor

• 1.
  Structure and roleof the Processor
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  Basic Points ProgramControl Unit – fetches instructions from the memory and executes them one at a time. Arithmetic and Logic Unit – Performs the arithmetic and logical tasks (the calculator) Registers – Very fast memory on the actual processor which stores both the program being carried out and the variables being worked on. (some dedicated some general purpose) Internal Clock – linked to the system clock and governs the rate at which the processor does things. Internal Buses – link the control unit, ALU and registers. Logic Gates – used to control the flow of data.
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  Registers Very fastmemory on the actual processor Very small storage capacity normally measured in kB (1024kb, i.e. 1Mb) General purpose – for storing and working on data. Dedicated registers – required for processor to keep track of what it’s doing, program counter, error checking etc (some can be written to by programs others can’t.)
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  Actual registers Stackpointer (SP) Program Counter (PC) Status Register (SR) Accumulator (ACC) Current Instruction Register (CIR) Memory Address Register (MAR) Memory Buffer Register (MBR)
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  System Clock andclock Speed Every PC has a quartz clock (like a pocket watch) The processor takes the external clock cycle and multiplies it for it’s internal use Some instructions take more than one clock cycle to perform, the processor regulates this. Clock speed is often in the region of 2GHz (currently)
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  Word Length Aword is a collection of binary digits Information and instructions are stored in words Larger words allow larger pieces of data to be worked on in any given cycle
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  Bus Width Wordlength and bus width are linked Bus width is the number of wires connecting the components Wider busses can carry more data per cycle
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  Increasing clock speedand Moore’s Law Moore’s law predicted that clock speed would increase by a factor of 10 every 3 years? This broke in 2000, over solutions had to be found. Quantum physics got in the way restricting how small you can make electric components before you loose track of your electrons.
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  Multicore The argumentwas that if you can’t make the chips faster (smaller) then you can have two or more running at the same time. It has faults Programs are rarely optimised to use both chips Power consumption is much higher
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  Word Length andbus width Longer word lengths result in more available addresses and more data available to be processed per cycle. They increase the speed but not as a direct multiplier ( double the word length does not necessarily double the speed) Wider busses have a similar affect to longer words (larger busses are required to provide and move longer words).