Systems architecture (1.1) GapFill

In a computer system, components are arranged so that the CPU is connected to input and output devices as well as to  an external clockan embedded systema program counterdata storage. The CPU is responsible for processing all of the operations that need to be carried out by the computer and is composed of the  control busRAMdata busALU (Arithmetic Logic Unit), the CU (Control Unit), registers and  cacheread-onlysecondaryvirtual memory.

The CPU runs in a fetch-execute cycle to retrieve one instruction, carry out that instruction, retrieve the next instruction and so on. The CPU uses  registersALUclocksheatsinks to store the data that is used in this process. The fetch-execute cycle is carried out as follows:

• The memory address of the next instruction to be executed is copied from the  CUALUPCMDR to the MAR
• This value is  copied to the MARincreased by 1copied to the MDRdoubled while the data stored in the memory location pointed to by the MAR is copied into the MDR
• The instruction is copied from the  MDRPCALUCU to the CIR
• The instruction is then decoded by the  cache memoryaccumulatorCUALU
• The instruction is executed

Factors which affect the performance of the CPU include the number of  coresusersinput/output devicesbuses, the CPU's  cacheaccumulatorclockmemory speed and the amount of available  cache memoryRAMROMsecondary storage.

Sometimes a computer may not act as a standalone device, but instead be built into a larger device to perform some specific task. This sort of computer is known as  an embedded systeman iterative systeman open-source systema nested system.