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 clocka program counterdata storagean embedded system. 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  cachesecondaryvirtualread-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  heatsinksregistersALUclocks 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  PCALUCUMDR to the MAR
• This value is  increased by 1copied to the MDRdoubledcopied to the MAR while the data stored in the memory location pointed to by the MAR is copied into the MDR
• The instruction is copied from the  PCALUCUMDR to the CIR
• The instruction is then decoded by the  accumulatorcache memoryCUALU
• The instruction is executed

Factors which affect the performance of the CPU include the number of  input/output devicescoresusersbuses, the CPU's  cacheaccumulatorclockmemory speed and the amount of available  cache memoryRAMsecondary storageROM.

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.