M3: C Debugging and Process Management

Question 1

Process context :

Answer 1

the snapshotted state of a process, which includes its data, memory utilization, and execution progress. The process context must be saved
when the OS wants to stop running a process, and it gets reloaded when the OS
resumes running the process.

Question 2

Virtual address:

Answer 2

mapped to physical addresses using a data structure called a “page table”. Creates a consistent format for the OS to manage the memory of all processes. Includes the heap, stack, code segment, data segment, and kernel
space.

Question 3

Disk

Answer 3

magnetic or optical storage for data. Disk storage is slower than your main memory storage, but is cheaper and stores data even when the computer is turned off.

Question 4

File descriptors

Answer 4

used as handles to files by processes
○ STDIN : defaults to keyboard input
○ STDOUT : defaults to printing output on your monitor/terminal

Question 5

Context switch:

Answer 5

the OS switches the process being executed. Context switches begin with a TRAP, which is a set of instructions that cause the computer to transition from user mode to kernel mode. Next, the OS saves the current
process context in it’s PCB, loads in the context of the next process’s PCB, resumes this next process, and transitions back to the user mode. Context
switching creates overhead.

Question 6

Process state

Answer 6

running, blocking, or ready. Each state has its own process
queue in the OS.
○ Running : instructions for this process are being executed by the CPU.
○ Blocked : process is waiting on I/O access, user input, or some other condition that cannot be met immediately, but is required to continue executing.
○ Ready : the process has all it needs to run and is waiting for CPU access.

Question 7

Preemption

Answer 7

when a process becomes ready, immediately give it an opportunity to run, regardless of any processes already running or processes ahead of it in the ready queue

Question 8

OS Scheduler:

Answer 8

most OSes have a finite time-slice for which processes can run before they are switched out. Larger time slices reduce the overhead of context switching, however cause longer wait times for new processes that wish to run.

Question 9

Prioritization

Answer 9

technique used in scheduling to ensure that urgent processes gain “fast passes” to the CPUs. Different priority processes may be placed in different priority queues. The priority level is an assigned number in a range of possible values that depends on the OS

Question 10

Bytestream abstraction

Answer 10

an abstraction in Linux, in which all data is sent to and

read from devices as a sequence of bytes

Question 11

Write()

Answer 11

accepts a file descriptor as an input. Returns the number of bytes written to the location specified by the file descriptor. Variations and additional syntactic
information are specified in the man pages.
○ fwrite() : buffered write

Question 12

Read()

Answer 12

Read() : accepts a file descriptor as an input. Returns the number of bytes read from the location specified by the file descriptor. Variations and additional syntactic information are specified in the man pages.
○ fread() : buffered read

Question 13

Disk controller:

Answer 13

A disk controller is the controller circuit that connects the CPU with the actual hard disk. The controller typically runs firmware, which is software written in low-level language that controllers actual hardware. The controller interacts with the disk device drivers running in the operating system by sending/receiving data to/from disk to applications

Question 14

Contents of PCB

Answer 14

1. Execution Context: SP, PC, Compute register values, segment register values, status(running, blocked ready)
2. Memory Context: Pointer to page table
3. Open File Descriptor Table

Question 15

When does Context Switch occur

Answer 15

1. Currently running process makes a system call and is blocked
2. Currently running process terminates
3. HW or SW interrupt happens
4. Current process used up its current “time slice

Question 16

Difference Signal vs Interrupt

Answer 16

Interrupts are similar to signals, the difference being that signals are used for inter-process communication (IPC), mediated by the kernel (possibly via system calls) and handled by processes, while interrupts are mediated by the processor and handled by the kernel.
Interrupt = no return value, unexpected, hardware generated