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 embedded systeman external clocka 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 busALU (Arithmetic Logic Unit)RAMdata bus, the CU (Control Unit), registers and  virtualsecondarycacheread-only 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  clocksregistersALUheatsinks 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  MDRPCALUCU to the MAR
• This value is  copied to the MARincreased by 1doubledcopied to the MDR while the data stored in the memory location pointed to by the MAR is copied into the MDR
• The instruction is copied from the  PCCUALUMDR to the CIR
• The instruction is then decoded by the  ALUaccumulatorCUcache memory
• The instruction is executed

Factors which affect the performance of the CPU include the number of  busescoresinput/output devicesusers, the CPU's  memorycacheaccumulatorclock speed and the amount of available  ROMsecondary storageRAMcache memory.

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 open-source systeman embedded systeman iterative systema nested system.