Unit 1 - System Architecture✔️ Flashcards
Three example of input devices?
Keyboard,scanner,microphone
Three example of output devices?
Speakers,display or printer
What is the cpu?
Central processing unit - process input,store data and output results it is the brains of the computer and executes instructions
How did early computers store data to be worked on?
Before 1943 early computers stored data to be worked on in memory - the program was not stored - instructions were input one at a time usings switches and executed one at a time
Who is von Neumann and what did he do?
• In 1943-44, mathematician von Neumann had the idea of storing the program instructions as well as the data in memory
• The stored-program computer was born
How does Von Neumann architecture work?
Program instructions and the data the programs are using are both stored in the same memory - the CPU accesses both instructions and data from the same RAM
Main components of the CPU?
• Control Unit
• Arithmetic-Logic Unit (ALU)
• registers
• Cache
What is the CPU’s register?
• A register is a very fast memory location in the CPU itself
What is a cache?
• Cache is located on the CPU – it is slower to access than registers but faster than RAM
What are the main registers in the CPU?
•Program Counter (PC)
• Memory Address Register (MAR)
• Memory Data Register (MDR)
• Accumulator
What does the program counter do?
holds the address of the next instruction to be executed
What does the memory address register do - MAR?
holds the memory address of the current instruction to be executed, and then the data that it uses, so that these can be fetched from memory
What does the memory data register do - MDR?
holds the actual instruction, and then the data that has been fetched from memory
What does the acccumulator do?
holds the result of an instruction before it is transferred to memory
What does the control unit do?
• The control unit coordinates and controls all of the activities taking place within the CPU
List three things the control unit does?
• It decodes instructions and executes them
• It receives signals from the system clock
• It directs the timing and control of other parts of the CPU
What is the purpose of the arithmetic logic unit - ALU?
The ALU or Arithmetic Logic Unit is where the actual arithmetic operations are done - It also carries out logical operations such as those including AND, OR and NOT
What is the fetch - decode - execute cycle?
Three operations operated by the cpu:
• FETCH – causes the next instruction and any data involved to be fetched from main memory
• DECODE – decodes the instruction
• EXECUTE – the instruction is executed
What does the program counter do?
• The Program Counter holds the address of the next instruction to be executed - increased by 1 as soon as the instruction has been fetched
What is the purpose of the accululator - ACC?
The accumulator (ACC) is where arithmetic and logic results are temporarily stored
Explain in depth what happens during the fetch stage of Fetch,decode,execute cycle?
1) the memory Addresss held in the program counter is copied into the MAR
2) the address in the program counter (PC) is then increased by 1 - the PC now holds the address of the next instruction to be fetched
3)processor sends a signal along the address bus to the memory address held in the MAR
How does the MAR and MDR work together?
The two work together; The MAR knows where to look for data in RAM, the MDR keeps hold of that data until it’s ready to be used by the CPU
Three factors that affect CPU performance?
• Clock speed
• Processor cores
• Cache
What is clock speed?
Cycles per second measured in hertz (Hz) - faster clock speed - faster the instructions are processed
