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COMP124 > Topic C > Flashcards

Topic C Flashcards

1
Q

What is multiprogramming?

A
  • Loading several programs into memory simultaneously, all sharing a single CPU
  • when the running program can’t continue (waiting for I/O) switch to another program
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2
Q

What is Multi-Access Time Sharing?

A

Each program has time slices. The program will run for a specified amount of time that’s dictated by the operating system then switch into waiting after it’s time slice is up

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3
Q

How long are time slices?

A

milliseconds long

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4
Q

what does the CPU switching rapidly between processes do?

A

It gives the illusion of uninterrupted execution in parallel

- makes it seem like multiple programs are running at once

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5
Q

What is the idea of a time slice?

A

the OS will split process time into a fixed quantum. At the end of a time slice the CPU sends an interrupt to the OS which puts a bit of its own OS code onto the CPU this code swaps out the running process and puts a new process onto the CPU, sets up the instruction pointer to wherever it needs to go and that program runs on the CPU

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6
Q

What is an interrupt

A

an automatic call of a sequence of instructions to deal with an event occurring outside normal program execution

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7
Q

what is the ISR

A

The sequence of instructions stored in that reserved area of memory

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8
Q

What is the interrupt service routine also known as?

A

the interrupt routine or interrupt handler

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9
Q

How do we protect the register values of the program that was running when an interrupt happened?

A
  • we save them all in the process control block

- this is a table of descriptors one for each process maintained by the OS

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10
Q

What happens during a context switch?

A

The state of the current program gets stored in its process control block.

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11
Q

What is the difference between programs and processes

A
  • A program is a static thing that the programmer writes, it could be source code or object code
  • the process is the running version of a program
  • A single program can have multiple processes
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12
Q

What does an OS structure consist of?

A
  • A central kernel
  • A set of processes
  • system calls
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13
Q

What does the kernel do?

A

performs low level, frequently needed activity. Performs 4 processes in particular that help to keep the computer under control

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14
Q

What does the system calls do?

A

allows a particular process wants to spawn another process to do something.

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15
Q

What is the bootstrap program

A

it reads from the OS from disk and puts it into memory. It loads the IP and points it to the first instruction of the OS itself

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16
Q

What is the command interpreter or shell?

A

It’s a normal user level process that might have some built in commands but usually it waits for the user to request to run a program/series of programs and it will trigger the processes that are needed to make that happen.

17
Q

how do we request the command interpreter’s services?

A

Via System calls

18
Q

What are the 5 major components of the OS

A 
The processor manager
The memory manager 
The file manager 
The device manager 
The user command interface
19
Q

What are the 4 managers inside an OS?

A 
The processor manager
The memory manager 
The file manager 
The device manager 
(the network manager is the 5th which is part of more modern systems)
20
Q

What tasks must each subsystem manager must perform?

A
  • monitoring of resources
  • enforcement of policies that determine who gets what resources
  • allocation of resources
  • de-allocation of resources
21
Q

What does the memory manager do?

A
  • preserves/protects space in memory occupied by the OS
  • checks validity of each request for memory space
  • allocates memory for legal requests
  • keeps track of which users are using which sections of memory
  • de allocates memory that’s no longer needed
22
Q

What does the processor manager do?

A
  • creates processes when necessary to carry out tasks
  • performs initialisation of new processes
  • keeps track of processes’ status
  • assigns processes to the CPU
  • changes state of a process
  • Handles termination of processes
  • handles inter-process communication
  • manages prioritisation of processes
23
Q

What does the device manager do?

A
  • allocates the system’s devices
  • deals with multiple requests for the same device
  • communicates with devices during operation
  • deallocates devices when no longer needed
24
Q

What does the file manager do?

A

f

25
Q

What does the network manager do?

A
  • provides facilities for users to share resources while controlling access to them
  • has a network stack that holds all of the protocols in TCP/IP and retrieving an IP address, making sure you have an IP address, making sure you know what your DNS are.
26
Q

What does each process have as part of it’s process descriptor?

A
  • they all have a different ID so that the OS can identify them programmatically
27
Q

What does the device manager do?

A
  • allocates the system’s devices
  • deals with multiple requests for the same device
  • communicates with devices during operation
  • deallocates devices when no longer needed
28
Q

What are the three main states?

A

running, ready, blocked (waiting)

29
Q

What does the network manager do?

A
  • provides facilities for users to share resources while controlling access to them
  • has a network stack that holds all of the protocols in TCP/IP and retrieving an IP address, making sure you have an IP address, making sure you know what your DNS are.
30
Q

What does each process have as part of it’s process descriptor?

A
  • ## they all have a different ID so that the OS can identify them programmatically
31
Q

What does the Process Control Block contain?

A
  • unique process ID
  • process state
  • position in memory
  • accounting stats (time used)
  • resources allocated
  • register values?
32
Q

What are the three main states?

A

running, ready, blocked (waiting)

33
Q

How many processes are in each state?

A

Only 1 in the running state, many in the ready state and many in the blocked/running state

34
Q

How do interrupts effect processes in each state

A
  • a process in the running state will receive an interrupt saying its time slice is up and to move into the blocked(waiting) state
  • a process in the blocked state will receive an interrupt telling it it has received what it was waiting for and to move into the ready state

COMP124 (9 decks)

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