Hardware - Computer Architecture Flashcards
what is the role of the CPU in a computer
continuously processes instructions and data that are inputted by repeatedly carrying out the fetch-execute cycle in order to output a result
what is meant by a microprocessor
a type of integrated circuit on a single chip that processes instruction
what are the 5 key elements of Von Neumann architecture:
- data + instruction are both stored as binary digits
- data + instructions both stored in primary memory
- instructions are fetched one at a time and in order (sequentially)
- cycle continues until no more instructions are available
what components are in the CPU
- ALU (Arithmetic Logic Unit)
- Control Unit
- Clock
- Registers
- Address, Data and Control Buses
what is the function of the ALU
- carries out mathematical + logical operations on data, including:
- Mathematical = ADD, SUBSTRACT …
- binary shifts
- Logical = AND, OR , NOT
- compares values held in registers
what is the function of the accumulator (ACC)
- register in which results of operations carried out in the ALU are ** temporarily stored** for quicker retrieval
- one of several general-purpose registers
what components are in the ALU units
- MDR
- ACC
function of the CU
- coordinates all of the CPU’s actions in the fetch-decode-execute cycle and decodes instruction
- sends + receives control signals to fetch + write data
what is the function of the Clock
- Electronic unit that synchronises + regulates the speed and timings of all signals + computer functions
what is the function of Registers
- very small, very fast memory locations
- registers built into the CPU chip to temporarily store memory addresses, instructions or data
- used in the fetch-decode-execute cycle for specific purposes
what does PC stand for
Program Counter
what is the function of the Program Counter
- is a register that golds the memory address of the next instruction to be processed
what is MAR
Memory Address Register
what is the function of the MAR
- holds address (location in memory) of the current instruction / piece of data to be fetched or stored
to which component does the MAR send the address to
to the main memory down the *address bus**
what does MDR stand for
Memory Data Register
what is the function of the MDR
-
temporarily holds data / program instruction when it is:
- fetched from memory OR
- data the is waiting to be written to memory
what must all data do when travelling to and from the main memory
travel down the Data Bus and pass through the MDR
what does CIR stand for
Current Instruction Register
what is the function of the CIR
- holds the instruction hat is currently being executed
- if MDR contains an instruction, this will be copied to the CIR
what are the 3 types of buses
- address
- data
- control
what is the purpose of an address bus
Unidirectional - carries memory addresses that identify where data is being read from or written to
what is the purpose of an data bus
Bidirectional - carries the binary 1s and 0s that make up the actual information being transmitted around the CPU / computer
what is the purpose of an control bus
Bidirectional - carries command + control signals to and from one component to another in the CPU
what is the fetch-decode-execute cycle
- continuous repetitive cycle
- every CPU instruction is fetched from memory
- is then decoded by the Control Unit to find out what to do with it
- instruction is then executed
each operation carried out within the fetch-decode-execute cycle is regulated by what
a ‘tick’ or cycle of the CPU clock
describe in detail the stages of the fetch-decode-execute cycle
FETCH Stage:
1. The memory address held in the program counter is copied into the MAR
2. increment PC so that address is now for the next instruction can be fetched
3. processer sends signal to address in MAR to be sent along address bus to *main memory** –> where it waits to receive a signal from the control bus
4. CU sends a read signal along control bus to main memory
5. contents at address within memory is sent along the data bus and to the MDR
6. data received in MDR is copied to Current Instruction Register
7. data in CIR is decoded + executed –> results of processing are stored in the ACC
8. repeats
what components are in the CU
- PC
- CIR
- MAR
describe the steps within the Decode stage
- instruction held in CIR is inspected and decoded to work out what needs to be done
describe the steps within the Execute stage
- send address from CIR to MAR
- send data down the address bus to main memory for it to read –> CU sends read signal along control bus to main memory
- address sent along data bus to MDR
- contents of MDR are copied to the ACC to be carried out
