Week 3

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

Question 5

STDIN

Answer 5

defaults to keyboard input

Question 6

STDOUT

Answer 6

defaults to printing output on your monitor/terminal

Question 7

Context Switch

Answer 7

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 8

Multi-core

Answer 8

a system with multiple CPUs

Question 9

Process state

Answer 9

running, blocking, or ready. Each state has its own process
queue in the OS

Question 10

Running

Answer 10

instructions for this process are being executed by the CPU

Question 11

Blocked

Answer 11

process is waiting on I/O access, user input, or some other condition that cannot be met immediately, but is required to continue executing

Question 12

Ready

Answer 12

The process has all it needs to run and is waiting for CPU access

Question 13

Preemption

Answer 13

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 14

OS Scheduler

Answer 14

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 15

Prioritization

Answer 15

A 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 16

I/O

Answer 16

Refers to any interactions between your computer and external devices, such as keyboard, mouse, disks, printers, monitors. Linux assigns a unique file descriptor to each external device

Question 17

Bytestream abstraction

Answer 17

An abstraction in Linux, in which all data is sent to and read from devices as a sequence of bytes

Question 18

write()

Answer 18

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.

Question 19

fwrite()

Answer 19

buffered write

Question 20

read()

Answer 20

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

Question 21

fread()

Answer 21

Buffered read

Question 22

Disk Controller

Answer 22

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