Module 2

Question 1

Computer System Architecture

Answer 1

System Bus (Memory Controller -> Memory) -> CPU -> Disk Controller -> Printer Controller -> Tape-drive Controller

Question 2

Execution Sequence

Answer 2

Fetch -> Decode -> Execute - > Write results -> PC -> Repeat

Question 3

____ and ____ execute concurrently

Answer 3

I/O devices, CPU

Question 4

each _____ has a local buffer

Answer 4

device controller

Question 5

_____ moves data from/to main memory to/from the local
buffers

Answer 5

CPU

Question 6

_______ interrupts CPU on completion of I/O

Answer 6

device controller

Question 7

is a signal to the processor indicating an event that needs immediate attention

Answer 7

interrupt

Question 8

Interrupt handling process:

Answer 8

• The processor stops current execution
• Saves state/context
• Transfers control to an interrupt handler
• Resumes execution after handling

Question 9

transfers control to the interrupt service routine

Answer 9

Interrupt

Question 10

segments of code that determine
action to be taken for each type of interrupt

Answer 10

Interrupt Service Routine

Question 11

contains the address of service routines

Answer 11

Interrupt vector

Question 12

software generated interrupt caused either by an error or a
user request

Answer 12

Trap

Question 13

Types of interrupt

Answer 13

Polling
Vectored interrupt system

Question 14

refers to the process by which a program or system continuously checks the status of a device or
resource at regular intervals to determine if it requires attention.

Answer 14

Polling

Question 15

is a mechanism in computer systems where interrupts are handled using a specific address (vector) associated with the interrupt source

Answer 15

Vectored interrupt system

Question 16

Incoming interrupts are disabled while another interrupt is
being processed to prevent a _____

Answer 16

lost interrupt

Question 17

2 I/O Structures

Answer 17

Synchronous I/O
Asynchronous I/O

Question 18

• wait instruction idles CPU until next interrupt
• no simultaneous I/O processing, at most one outstanding I/O request at a time

Answer 18

Synchronous I/O

Question 19

after I/O is initiated, control returns to user program without waiting for I/O completion.

Answer 19

Asynchronous I/O

Question 20

holds type, address and state for
each device

Answer 20

Device Status table

Question 21

Used for high speed I/O devices
able to transmit information at
close to memory speeds

Answer 21

Direct Memory Access (DMA)

Question 22

3 Storage Structure

Answer 22

Main memory
Secondary storage
Tertiary Storage

Question 23

only large storage media that the CPU can access directly

Answer 23

Main memory

Question 24

extension of main memory that has
large nonvolatile storage capacity

Answer 24

Secondary storage

Question 25

rigid metal or glass platters covered with magnetic recording material.

Answer 25

Magnetic disks

Question 26

examples are Tape drives and Cloud backups

Answer 26

Tertiary Storage

Question 27

Storage systems are organized in a hierarchy based on:

Answer 27

Speed Cost Volatility

Question 28

process of copying information into faster storage system; main memory can be viewed as fast cache for secondary storage

Answer 28

Caching

Question 29

Storage Device Hierarchy

Answer 29

registers -> cache -> main memory -> electronic disks -> magnetic disk -> optical disk -> magnetic tape

Question 30

4 Hardware Protection

Answer 30

Dual Mode Operation I/O Protection Memory Protection CPU Protection

Question 31

Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly

Answer 31

Dual-mode operation

Question 32

two modes of operation

Answer 32

User mode Monitor mode (supervisor/kernel/system mode)

Question 33

execution done on behalf of a user

Answer 33

User mode

Question 34

execution done on behalf of operating system

Answer 34

Monitor mode (supervisor/kernel/system mode)

Question 35

These instructions are used for system-critical operations and are restricted to prevent unauthorized access by user programs.

Answer 35

Privilege Instruction

Question 36

Examples of Privileged Instructions

Answer 36

Interrupt Handling Modifying System Control Registers Changing CPU Mod

Question 37

Must ensure that a user program could never gain control of the computer in monitor mode, for e.g. a user program that as part of its execution, stores a new address in the interrupt vector

Answer 37

I/O Protection

Question 38

Must provide memory protection at least for the interrupt vector and the interrupt service routines

Answer 38

Memory Protection

Question 39

interrupts computer after specified period to ensure that OS maintains control

Answer 39

Timer

Question 40

Given the I/O instructions are privileged, how do users perform I/O?

Answer 40

Via system calls

Question 41

the method used by a process to request action by the operating system

Answer 41

system calls

Question 42

Interface between running program and the OS.

Answer 42

System Calls

Question 43

Operating Systems: How are they organized?

Answer 43

Simple Layered Microkernel Modular

Question 44

Only one or two levels of code

Answer 44

Simple

Question 45

Lower levels independent of upper levels

Answer 45

Layered

Question 46

OS built from many user-level processes

Answer 46

Microkernel

Question 47

Core kernel with Dynamically loadable modules

Answer 47

Modular

Question 48

4 Types of Kernel

Answer 48

Monolithic Kernel Microkernel Hybrid Kernel Exokernel

Question 49

Entire OS runs as a single program in kernel mode (Example: Linux, Unix)

Answer 49

Monolithic Kernel

Question 50

Only essential functions (process management, memory management) are in the kernel, while others run as separate user-space services (Example: Minix, QNX)

Answer 50

Microkernel

Question 51

Combines elements of monolithic and microkernels. (Example: Windows NT, macOS)

Answer 51

Hybrid Kernel

Question 52

Minimally manages resources, allowing applications to control hardware directly. (Example: MIT Exokernel)

Answer 52

Exokernel

Question 53

provides a lot of functionality in little space.–Not divided into modules, Interfaces and levels of functionality are not well separated

Answer 53

MS-DOS

Question 54

limited structuring, has 2 separable parts -Systems programs -Kernel

Answer 54

UNIX

Question 55

Moves as much from the kernel into “user” space

Answer 55

Microkernel Structure