Lecture 1

Question 1

Examples of Computer Hardware

Answer 1

CPU, RAM, Storage

Question 2

Operating Systems enable…

Answer 2

…the user to interact with hardware

Question 3

Examples of System/Application Programs

Answer 3

Compilers, Text Editors, Database Management Systems

Question 4

Operating Systems act as…

Answer 4

…Resource allocators and control programs

Question 5

What useful functions do operating systems provide on their own?

Answer 5

None (Waits for user or programs to do something)

Question 6

Resource Allocator

Answer 6

• Manages all resources
• Decides between conflicting requests for efficient/fair
  resource use

Question 7

Control Program

Answer 7

Prevents errors and improper use of the computer

Question 8

Operating System Goals

Answer 8

• Make system convenient to use (more important for
  PCs)
• Use hardware efficiently (more important for shared
  systems)
• Sacrifice performance to improve lifetime of resources
  (Only done sometimes)

Question 9

CPUs and device controllers connect through a bus to…

Answer 9

…Shared memory, which becomes a means of communication

Question 10

Steps of an I/O operation

Answer 10

• CPU sends read request (CPU and I/O device
  controllers execute concurrently)
• Incoming data written to I/O device’s local buffer
• When I/O complete, send CPU an interrupt
• CPU services interrupt, read from I/O local buffer to
  main memory

Question 11

Interrupts are ____ events

Answer 11

Asynchronous

Question 12

On an interrupt, OS preserves state of CPU by storing ____ and the ____

Answer 12

Registers and the Program Counter

Question 13

Interrupt is processed by calling the corresponding…

Answer 13

…ISR (Interrupt Service Routine)

Question 14

How would OS locate the correct ISR?

Answer 14

• An interrupt vector is stored at a known location in
  memory
• Each entry contains the address of an ISR
• Interrupt number is mapped to an entry in interrupt
  vector

Question 15

What does interrupt (or event) driven mean?

Answer 15

OS sits idle until something happens

Question 16

Interrupts are generated by…

Answer 16

…Hardware devices

Question 17

Traps/Exceptions are software-generated interrupts due to…

Answer 17

…Errors, or requests for OS services (system calls)

Question 18

4 potential problems with user code

Answer 18

• Can be buggy/malicious
• Can corrupt hardware
• Can corrupt OS
• Can corrupt or access other users’ software/files

Question 19

How to protect from user’s code?

Answer 19

Allow only OS to perform certain operations

Question 20

OS operates in two modes: ____ and ____

Answer 20

User and Kernel

Question 21

____ in hardware indicates OS’ current mode

Answer 21

Mode bit

Question 22

What are privileged instructions?

Answer 22

Instructions that are predetermined to possibly cause harm

Question 23

Hardware executes privileged instructions only in…

Answer 23

…Kernel mode

Question 24

OS ensures ____ and ____ of privileged instruction before execution

Answer 24

Safety and correctness

Question 25

How can users access privileged instructions?

Answer 25

System calls, which use software-generated interrupts

Question 26

When an interrupt or trap is generated, control is transferred to…

Answer 26

…the OS