Week 5: Introduction to Operating Systems

Question 1

Name the disadvantages of Serial Processing?

Answer 1

Scheduling means time is wasted and it takes a long time to set up.

Question 2

Describe the role of the monitor in Simple Batch Systems?

Answer 2

Controls sequence of events and gives control to jobs.

Question 3

Describe Simple Batch Systems?

Answer 3

No longer direct access to processor.
Processor fetches and executes from either monitor or job.
This means main memory and processor time must be given to the monitor.
This improves utilization, however.

Question 4

Compare Uniprogramming and Multi-Processing?

Answer 4

Uniprogramming: Program waits for I/O.
Multi-Processing: Processor switches to another job while one job waits for I/O.
Needs enough memory for OS (resident monitor) and one user program.

Question 5

What is the principle objective and source of directives (to OS) of Batch Multiprogramming?

Answer 5

Principle Objective: Maximize processor use.

Source of directives: Job control language commands (provided with the job).

Question 6

What is the Principle Objective and Source of Directives (to OS) of Time Sharing Systems?

Answer 6

Handle multiple interactive jobs, processor time shared among multiple users.
Principle Objective: Minimize response time.
Source of Directives: Commands entered at terminal.

Question 6

What is the role of the Operating System?

Answer 6

Manage the set of resources for movement, storage and processing of data.

Question 7

What are some of the services an Operating System provides?

Answer 7

Program development and execution.
Controlled access to I/O devices, files and system.
Error detection and response.
Accounting.

Question 8

What happens upon start-up of an Operating System?

Answer 8

Bootstrap.
Firmware initializes CPU registers, device controllers and memory contents.
Kernel is loaded into memory.

Question 9

What is a system daemon?

Answer 9

A service provided outside the kernel.

Loads at boot time and runs entire time the kernel is running.

Question 10

What occurs during an interrupt?

Answer 10

CPU transfers execution to fixed location (starting address of service routine).

Question 11

State the difference between hardware and software interrupts?

Answer 11

Hardware: Sends interrupt signal to CPU at any time.
Software: Sends interrupt signal when executing special operation (system call).

Question 12

How does multi-tasking work in the operating system?

Answer 12

Several jobs kept simultaneously in memory.

CPU Scheduler decides which job to bring into memory from disk to be executed (virtual memory used).

Question 13

What is the User Mode in an Operating System?

Answer 13

Contains user programs.

Certain memory/instructuions protected/not executed.

Question 14

What is the Kernel Mode in the Operating System?

Answer 14

Contains monitor.
All memory/privileged instructions accessed.
Hardware detects violatiom of modes.

Question 15

How are programs executed, in terms of storage, in the Operating System?

Answer 15

An instruction is fetched and stored in the instruction register.
This is decoded, causing further operands to be fetched and stored in other registers.
The memory unit only sees streams of addresses.

Question 16

What is a Device Controller?

Answer 16

Devices connect to these, which connect to the CPU via a common bus.
Moves data between peripheral devices it controls and local buffer storage.
Have a local buffer storage as well as special purpose registers.

Question 17

What is a Device Driver?

Answer 17

Stored in kernel.
Understands device controller.
Provides OS with a uniform interface to device (same no matter the device).

Question 18

What is the Programmed I/O mechanism?

Answer 18

Processor polls controller status.
When I/O is finished, data is transferred between I/O modules, processor and main memory.
Processor has special instructions to control I/O device, test status and transfer data.
Disadvantage: Processor is busy.

Question 19

What is the disadvantage of Interrupt Driven I/O?

Answer 19

Not suitable for bulk data, disk I/O for example.

Question 20

What is Direct Memory Access?

Answer 20

Transfers data directly from I/O device, to controller buffer, to main memory.
No intervention from the CPU.
Advantage: CPU is free, with only a single interrupt needed.
Disadvantage: DMA controller and processor share the bus connecting different hardware components, resulting in slowdown.

Question 21

Describe Multiprocessor Systems?

Answer 21

Share bus, clock, memory and peripherals.
Parallel.
Increased throughput and reliability (graceful degradation).
Economy of scale.

Question 22

What is the processor relationship in Asymmetric Multiprocessor Systems?

Answer 22

Boss-worker.

Each processor is assigned a specific task.

Question 23

What is the processor relationship in Symmetric Multiprocessor Systems?

Answer 23

Peer to peer.

Each processor utilized and has equal chances of being used.

Question 24

What are the advantages of Multicore Systems?

Answer 24

Faster on chip communication.

Less power.

Question 25

Described Clustered Systems?

Answer 25

Loosely coupled.
Share storage.
(A)symmetric.
Allows for high performance computing and parallelization of applications.
High availability.

Question 26

Described the MS-DOS (Simple) structure for OS design?

Answer 26

Provides most functionality in the least space.

No modules, not well separated functionality = dangerous.

Question 27

Described the UNIX (non simple) structure for OS design?

Answer 27

Two separable parts - system programs and kernel.
Kernel consusters of everything below system-call interface and above hardware (file system, scheduling etc.)
Disadvantage: Large number of functions for one level.

Question 28

Describe the Layered Approach (theoretical) structure for OS design?

Answer 28

Layer 0 = hardware
Layer N = UI
Each layer uses functions from lower layers.

Question 29

Describe the Microkernel structure of OS design?

Answer 29

Moves as much from kernel to user space
Communication between user modules by message passing.
Advantages: Easy to extend/port to new architectures, reliable (smaller kernel mode), secure.
Disadvantage: Overhead

Question 30

Describe Modules structure of OS design?

Answer 30

Loadable kernel modules.
OOP approach.
Modules communicate through known interfaces.