Module 4

Question 1

Control registers

Answer 1

Registers in the CPU that are used to store control information on state of program execution, for example, the program counter and stack pointer.

Question 2

Data registers

Answer 2

Registers in the CPU that are used to store the intermediate data used when executing instructions.

Question 3

System call

Answer 3

executed in kernel mode and thus requires a context switch. Provide an interface for the user to interact with the OS and request functionality. Each system call has a call number, which is used by the system call dispatcher to lookup the code associated with the invoked system call.

Question 4

Blocked queue

Answer 4

a process is placed on the blocked queue, maintained by the OS, if it is waiting for some condition to be true before it is able to proceed in its execution; one example is a process waiting for a response from an I/O device that is not ready

Question 5

TRAP call

Answer 5

a series of assembly instructions leading to he privilege bit being flipped in the CPU to switch it from operating in user mode to kernel mode

Question 6

CPU cache

Answer 6

stores copies the data that is frequently accessed by this processor

Question 7

Interrupt

Answer 7

a notification to the OS for an event that requires servicing; the
interrupt may originate from a hardware device or software condition

Question 8

Interrupt identfier

Answer 8

used by the OS to map the interrupt notification to the
appropriate handler for the event

Question 9

Disk device driver

Answer 9

device drivers are used as an interface between the hardware and software to allow the operating system to ignore the specific details of the hardware component being used

Question 10

Interrupt handler

Answer 10

A function that is run whenever a particular type of interrupt is invoked and received by a process.

Question 11

Segmentation faults

Answer 11

a failure that occurs when the program attempts to access a restricted portion or memory, or read/write illegally (e.g. write to a read-only location of memory). This is a means of notifying the OS of the illegal action, and results in memory protection for the machine.

Question 12

Pointer

Answer 12

store the addresses or memory locations of variables

Question 13

Dereferencing

Answer 13

use the address value from the pointer to
access the data in the memory location

Question 14

Hardware interrupts

Answer 14

interrupts that are generated at the hardware level,
typically in response to an external event such as a clock tick or completion of a
disk request.

Question 15

Clock pulse

Answer 15

All motherboards usually come with its own clock. Every clock tick
generates a pulse which is delivered to the operating system in order to advance
current time and invoke the scheduler.

Question 16

Illegal instruction

Answer 16

A hardware instruction that is disallowed, for example, an
instruction that cannot be run due to lack of privileges or an instruction that
touches memory location that is not available to the current process.

Question 17

Scheduler

Answer 17

a piece of software that resides in the scheduler that decides which
process to run next

Question 18

Interrupt service routine

Answer 18

whenever a hardware interrupt arrives, it is delivered
to the operating system where there is a piece of software called the interrupt service routine that decides how to handle the interrupt. This is analogous to the signal handler.

Question 19

Hardware interrupt ID

Answer 19

a unique identifier assigned to each hardware interrupt. The interrupt service handler uses this to decide how to handle the specific interrupt.

Question 20

Custom handlers

Answer 20

signal handlers that provided in user space and is customized by the application for handling the particular signal.

Question 21

Default handlers

Answer 21

signal handlers that are default in the operating system.

Question 22

Signal relaying

Answer 22

sending one signal from one process to another through the
kernel.

Question 23

Peemptible signal handlers

Answer 23

when a signal handler is running and a new
signal arrives, rather than complete running the signal, if the handler is “preemptible”, it means we can stop the current handler and deal with the signal first.

Question 24

Signal blocking

Answer 24

a signal being buffered and delayed at the operating system and not delivered to the process until it is explicitly unblocked.

Question 25

Disk operation

Answer 25

an operation requiring a response from the external disk
memory