Operating system and computer architecture Flashcards
What is an Operating System?
Software running in the background of a computer. It manages many of basic functions. It also makes it possible to communicate between HW and SW
Give examples (5) of what basic functions OSs control
HCL (Human computer interface), Multitasking, Multiprogramming, Interrupt handling, Real-time processing
What type of OS is Windows?
Single-user multitasking operating system
What does ROM stand for?
Read only memory (can’t be changed)
What does ROM run?
BIOS (basic input-output system), processor, hardware, processor, internal memory
What is an interrupt?
A signal sent from a device or from software to the processor
Give 4 examples of interrupts
- A disk drive is ready to receive more data
- An error has occurred, such as a paper jam in a printer
- The user has pressed a key to interrupt the current process - ALT F4
- A software error has occurred - an exe file couldn’t be found
What does the proccessor do with the interrupt?
The procesor either carries on with what it was doing or stops to service the device/program that generated the interrupt
Why are interrupts useful?
They allow computers to carry out many tasks or to have several windows open at the same time
Give an example of how an interupt could be useful?
An example would be downloading a file from the internet at the same time as listening to music at the same time.
How is a status of the current task saved as an interrupt is serviced?
It is done using an interrupt handler, once the interrupt is serviced the paused task continues.
What are Buffers?
They are used in computers as a temporary memory area
Why are Buffers essential?
They are essential since hardware devices operate at much slower speed than the processor. If it wasn’t for buffers prcessors would spend the majority of their time idle, waiting for hardware to comple its operation
Give an example of Buffers being used.
For example, when streaming a video from the internet. It ensures that the video play back doesn’t keep on stopping to wait for fata from the internet.
When did John von Neurmann develop the idea of a sotred program computer?
1945
What was the concept called that John von Neumann came up with?
Von Neumann Architecture
What was the ideas within the Von Neumann Architecture concept?
To hold programs and data in a memory. Data would then move between the memory unit and the processor.
What links the processor and memory units?
Buses
What is an adress bus?
Carries signals relating to addresses between the processor and the memory
In which direction is data sent down an adress bus?
Unidirectional (signals travel in one direction only)
What is a data bus?
Sends data beween the processor, the memory unit and the input/output devices
In which direction is data sent down a data bus?
Bi-directional (data can travel in both directions)
What is a control bus?
It carries signals relating to the control and coordination of all activities within the computer
In which direction is data send down a control bus?
Unindirectional and Bi-directional due to internal connections within the computer architecture
What are Addresses?
They indicate where the data is stored
Why are registers needed?
So that data can be manipulated within the computer
What are registers?
They are high-speed storage area within the computer. All data must be represented in a register before it can be processed
What is the difference between Adresses and contents?
Addresses will uniquely identify every location in the memory, and the contents will be the binary value stored in each location
What are the five registers within the memory unit?
- MAR
- MDR
- ALU
- PC
- CIR
What are the two registers within the memory unit?
- MAR
- MDR
What are the two registers within the memory unit?
- MAR
- MDR
What does MAR stand for?
Memory adress register
What does MDR stand for?
Memory data register
What does ALU stand for?
Arithmetic and Logistic Unit
What does PC stand for?
Program Counter
What does CIR stand for?
Current instruction register
What does an MAR do and give an example
Its where adresses are stored. The address of location 1111 0001 to be read from it is first written into the MAR. A read signal is sent to the computer memory using a control bus. The contents of memory location are then put into the MDR
What does an MDR do?
10010101 has to be written into the memory location with the address 1111 1101; so this address is now written into the MAR. A write signal is sent to the computer memory using the conrol bus and this value will then be written into the correct memory location.
In terms of design what does the processor contain?
The ALU ( Arithmetic and Logic Unit)
What does the ALU do?
It allow arithmetic and logic operations to be carried out
What does the Control Unit do?
It reads and instruction from memory (the address of the location where the instruction can be found is stored in the PC (program counter). This instruction is then interpreted.
Describe the Fetch-execute cycle
First the processor fetches some data and instructions from memory and stores them in suitable registers. Both the address bus and the data bus are used in this process. Once this is done, each instruction needs to be decoded before finally being executed.
What does the CIR (current instruction register) do?
It contains the current instruction being processed.
What does the PC (Program counter) do?
Contains the address of the next instructions to be executed
Describe the Fetch process.
THe next instruction is fetched from the memory address currently stored in the PC and is then stored in the CIR. The PC is then incremented so that te next instruction can be processed
Describe the execute process.
THe processor passes the decoded instruction as a set of control signals to the appropriate components within the computer system.
What are the two registers in the control unit?
PC and CIR
What is the register in the Processor
ALU
What does the control unit do?
It controls the operation of the memory, processor and input / output devices
