Operating systems

Question 1

What is an operating system?

Answer 1

It is a low-level software that lets a computer carry out its basic functions, such as scheduling.

Question 2

What are the functions of an operating system?

Answer 2

It has 3 important functions: 1. Provide a user interface, 2. Manage the hardware of the computer, such as CPU, memory, and hard drive, 3. provide services for the application softwares of the computer to work.

Other important functions:

1. Manages login and passwords
2. Memory management
3. Manages user accounts
4. Error handling
5. Multitasking

Question 3

What is an interrupt?

Answer 3

An interrupt is a signal sent from a hardware or software to the processor to let it know that an event has occurred that needs immediate attention.

When: disk drive is ready to receive more data, paper jam in a printer, software error

Question 4

Why is an interrupt important?

Answer 4

Interrupts allow the computers to carry out many functions at the same time.

It also makes sure that the processor knows of the errors that have occurred during operation, so that they can be fixed.

Question 5

What is a buffer?

Answer 5

A buffer is a temporary memory location where data is stored while being processed or transferred.

Question 6

Why is it important to have buffers?

Answer 6

It lets the computer function faster and in a smoother manner. Eg. when streaming a video from the internet, buffers make sure that the video does not keep stopping waiting for data to be transferred from the internet.

It lets the computer multitask - processor can carry out its functions while the buffer is being filled/emptied.

Question 7

What are the important components of the Von Neumann architecture? Explain the function of each.

Answer 7

1. Input/Output devices - receive input and give output
2. Processor - Component where operations are controlled and executed.
3. Control unit - Manages the movement of data into and out of the memory unit, also concerned with executing of instructions
4. Memory unit - Storage of data
5. Buses - Conductors that carry data and control signals within a computer system
6. Registers - Quickly accessible location to a computer, generally used for fast storage although they can be programmed to carry out specific functions.

Question 8

What is the stored program concept?

Answer 8

Von Neumann’s idea that program instructions and data can be stored in the main memory while instructions are fetched and executed one after another.

Question 9

What are the different types of buses and what is the function of each?

Answer 9

1. Address bus - Carries signals, unidirectionally, between processor and memory unit
2. Control bus - Carries signals that control and coordinate the activities of the computer; can be both bi and unidirectional
3. Data bus - Carries data between the processor, memory unit, and input and output devices; bidirectional carrying

Question 10

Describe each of the stages of the fetch execute cycle.

Answer 10

1. The CPU sends the PC to the MAR, and sends and read command, via the address bus
2. The memory unit responds to the read command by sending data stored in the memory location indicated by PC, via the data bus.
3. CPU copies data from the data bus to the MDR
4. CPU copies data from MDR to the IR
5. PC is incremented, so that it points to the next instruction in the memory.

CPU - Executes instructions to run programs.

PC - A register that contains the location of the instruction that is currently being executed.

Memory Address Register - Contains the address of the next item to be executed by the processor.

Memory Data Register - Contains instructions that is being fetched or that has just been received.

Instruction register - holds instructions to be decoded and executed.