Internal computer arvhitectures Flashcards
summarise Von neumann architecture
CPU, arrow, system bus, RAM, Instructions, Data
- shared memory space for instructions and data
- instructions and data stored in the same format
- a single control unit it processor follows a linear fetch, decode, execute cycle
- one instruction at a time
- registers are used as fast access to instructions and data
summarise the Harvard architecture
- instructions and data stored in separate memory units
- each has its own bus
- reading and writing data can be done at the same time as fetching an instruction
- used by RISC processors
disadvantages of harvard architecture
- no adaptability
- not appropriate for general or multi purpose machines as you can’t install and uninstall programs
what is the stored program concept
the idea that instructions are fetched one at a time from main memory and executed immediately by the processor in the sequential order
- program can be replaced by loading another program into memory
- contents in memory location can be interpreted as instruction or data
What happens during the Fetch stage of the Fetch-Execute cycle
- contents of PC transferred to MAR
- Address bus is used to transfer this address to main memory
- main memory content is transferred using the data bus
- contents of memory address location is loaded into MBR
- contents of MBR copied into CIR
What happens during the Decode stage of the Fetch-Execute cycle?
- The Control Unit decodes the instruction held in the CIR.
- : The instruction is split into the opcode and operand
What happens during the execute stage of fetch-decode-execute
- if necessary, data is fetched
- opcode identifies type of operation to be performed
- ALU is used to carry out the operation
- result stored in main memory
what does an instruction contain
an opcode and an operand
what does the opcode do
Tells the CPU what to do
what does an operand do
is a value or is data that will be used in an operation
what can the operand be
- the actual data that you’re performing the operation on
- a memory location where the data is found
whats the difference between direct and immediate addressing
- addressing mode 01 specifies that the data is an address, not a value (direct)
- addressing mode 00 specifies that data is a value, not an address (immediate), represented with a hashtag before the value
Why are registers used as a fast access to instructions and data in the von Neumann architecture?
Because it’s quicker to work with data in the CPU than it is to work with directly in memory
Examples of alternative architecture
- Parallel processing-where the processor carries out a single instruction on multiple data
- distributor computing
What could the operand contain?
It could contain the actual data or an address where the data is found