Systems Architecture GapFill

The CPU architecture is the term which describes how the components in the Central Processing Unit (CPU) are set out. The Von Neumann architecture is a computer system where all  programsdata and instructionsinformationinputs are stored in the same place as they are all in binary.

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 accumulatorportsdata 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   ALU (Arithmetic Logic Unitaddress busRAMROM, the CU (Control Unit), registers and   cachevirtualrandom accessflashmemory and the clock. The clock controls the speed at which the CPU processes instructions with one clock ‘tick’ representing one stage in the Fetch – Execute cycle.

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

• The address of the next instruction in memory is fetched and placed into a register
• The control unit(CU) decodes the instruction
• The instruction is then executed, which may involve calculation using the ALU or reading in more data or instructions.
• The process is then repeated

Factors which affect the performance of the CPU include the number of   busescoresbytesclocks, the CPU's   memoryclockcacheaccumulator speed and the amount of available   RAMremovable storagecache memorysecondary 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 open-source systeman embedded systema closed-source systema von Neumann system.

Computer systems use primary storage to store   all programs and data that is currently in usedata onto removable storage deviceseverything that is currently visible on the screenprograms and data that is not currently in use.

 Virtual memoryRAMFlash memoryMagnetic memory is volatile memory, meaning that when it loses power   the data it stores is erasedits data capacity is reducedthe data it stores is savedit becomes damaged. It is also random-access, meaning that the CPU can access   random memory locationssecondary storage as though it were main memoryall memory locations at onceany memory location in the same amount of time.   ROMFlash memoryRAMVirtual memory is read-only; it   can only be read by peripheral devicescannot be readcannot have data written to itcan only be read by internal devices. It is also a type of non-volatile memory.   Flash memoryVirtual memoryRAMROM is a type of memory that can be non-volatile without being read-only. This allows it to be used for secondary and removable storage. It uses transistors and electrons to represent data, and has faster access speeds than other types of memory used for secondary storage.

It is important for a computer to be able to store data for a long time, even when it is not in use.

RAM is unsuitable for this type of storage because it is volatile, and ROM is not enough on its own because it cannot be written to. Instead, various different types of   registerssecondary storagecache memorymain memory are often used as the main form of long-term storage for a computer.

 SSDsHDDsSD cardsRAM locations are a type of secondary storage with moving parts, these store data by using   a reflective diska magnetised diskRAMtransistors, and are widely used in PCs because they   are very durableencrypt all datacan store a lot of data for a low costnever corrupt data.

 CDsUSB drivesSSDsSD cards are also often used as a secondary storage device in PCs. They have higher data transfer rates, but are   read-onlysignificantly less energy efficientmore expensive per GBnot random access. 

 SecondaryMagneticSolid-stateOptical storage is mainly used for removable storage, such as CDs, which have a maximum capacity of 700MB, and   SD cardsUSB drivesDVDsBlu-ray discs, which have a maximum capacity of approximately 4.7GB (if they only use one layer). Another alternative is to use  cloud storageDVD storagebackup storageUSB storage, which means that the data together with other applications such as word processors or spreadsheets are available wherever there is an internet connection. The advantages of this method are that applications are always up-to-date however; the drawbacks are the need for an internet connection and the lack of control over keeping it secure.