Final

Question 1

What does STS stand for

Answer 1

Short term scheduler

Question 2

What does STS users care about

Answer 2

• Response Time
• Turnaround time
• Predictability
• Deadlines

Question 3

What does STS systems care about

Answer 3

• Throughput
• CPU Utilization
• Fairness
• Priority
• Balancing Resources

Question 4

What are two ways that STS processes decisions

Answer 4

– pre-emptive: a running process may be interrupted and moved from running to ready (timeslice interrupt)
– non pre-emptive: once a process is running, it continues until done, or blocked (for I/O
or OS service)

Question 5

What polices can STS operate under

Answer 5

• First come, first served (FIFO)
• Round Robin
• Virtual Round Robin
• Shortest job first
• Shortest remaining time

Question 6

What are the three types of message passing

Answer 6

• Blocking send, blocking recieve (good for tight sync)
• Non-Blocking send, blocking receive (generally most useful), good for client/server interactions
• Non-blocking send, non-blocking receive

Question 7

What are two ways we identify sender and recevier in messaging?

Answer 7

Direct Addressing: Targeted, must know them.

Indirect addressing: Mailboxes, use common data structure

Question 8

New class of scheduling for urgent processing

Answer 8

Real time scheduling. Usually these urgent processes are responding to events in the real world

Question 9

Name the 7 layers in OSI

Answer 9

7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

Question 10

What communicates on each layer of the OSI model?

Answer 10

Application: web applications
Presentation: http
Session: 80
Transport: TCP
Network: IP/packets
Data Link: Ethernet/frames
Physical: Cat5

Question 11

Real Time Scheduling must indicate timeliness, must have at least one of these

Answer 11

Deadlines:
Start time
End time
(rare it’s both)

Question 12

Two types of real time scheduling deadlines

Answer 12

Hard real-time (must)

Soft real-time (should)

Question 13

Real time system scheduling must by

Answer 13

preemptive and priority based

Question 14

Real time scheduling must work in the following model for scheduling

Answer 14

Real time operating systems

Question 15

What is deadlock

Answer 15

2 processes each waiting for the other to release a resource

-May be hardware or software

Question 16

Why does deadlock occur?

Answer 16

Problem occurs when processes follow a request → use → release model of resource utilization

Question 17

What is deadlock versus starvation

Answer 17

-Deadlock refers to the situation when
processes are stuck in circular waiting for the
resources.
-Starvation occurs when a process waits for
a resource indefinitely.

-Deadlock implies starvation but starvation
does not imply deadlock.

Question 18

What are the conditions for deadlock

Answer 18

• Mutual exclusion (one process may use resource at a time)
• Hold and wait: (process hold allocated resources while waiting)
• No Pre-emption (no resource may be forcible taken)
• Circular wait (a closed chain of process where one holds what the other needs)

Question 19

How can we prevent deadlock?

Answer 19

Prevention
Detection
Avoidance

Question 20

What do we currently do to prevent deadlock

Answer 20

Nada… Let the OS figure it out or just ignore it as it rarely happens

Question 21

Sequence of early programming

Answer 21

Op Codes (numbers only)
Assembly Language (names for program, like add, mov, cmp)

Question 22

What were the early program for translation

Answer 22

Translator: called assembler

Language called: Assembly Language

Question 23

High level languages

Answer 23

Java, C, C++, Python…

Question 24

What is software engineering

Answer 24

discipline devoted to best practices in design and

building of programs

Question 25

Programming practies

Answer 25

- Write code easy to read - Write code clear and easy to undertsand - Comment code - Write human readable form

Question 26

What is the compiler

Answer 26

Translates a higher level language (human readable source code – Fortran, C, Cobol, etc.) to machine (object) code – the whole program at once before it is loaded into memory.

Question 27

What is the interpreter

Answer 27

Translates a higher level language (human readable source code – Fortran, C, Cobol, etc.) to machine (object) code – statement by statement at runtime

Question 28

What is the assembler

Answer 28

Translates assembly language into machine (object) code.

Question 29

What is the loader

Answer 29

loads load modules into memory:

Question 30

What is the load module

Answer 30

Program that exist as a disk file, contains executable code

Question 31

What is the linker

Answer 31

resolve such undefined references by linking library object code with our newly created object code

Question 32

What are the different kinds of load modules

Answer 32

Absolute: program must be loaded into real memory at exactly the location it was built for Relocatable: delay that association (binding) until load time Dynamic Run-time:absolute addresses are calculated as needed at run time

Question 33

What are two types of linking

Answer 33

Static and Dynamic

Question 34

How do you get code into memory:

Answer 34

``` Basically, source code (1) gets translated into machine code (2) that goes to the linker (3). The linker than connects the machine code with preexisting libraries (4) creating the load module (5). The load module than “loads” the files into main memory (6). ```

Question 35

How much does a sector hold

Answer 35

typically 512 bytes

Question 36

How many sectors per track

Answer 36

63 on a hard disk

Question 37

What is the difference between track and sector

Answer 37

Track is the circular portion, where the sector is the stops in a track

Question 38

Cylinder-Head-Sector calc

Answer 38

cylinder*head*sector * bytes per sector | i.e. 6296 * 16 * 63 * 512 bytes per sector

Question 39

Average seek time per disk

Answer 39

3600: 8.5ms, Max is 20ms 7200: 4.17ms, Max 8.3 15000: 2ms, Max 4ms

Question 40

Explain difference between CAV vs CLV

Answer 40

Bits in tracks at outer edge farther apart than those on inner tracks. CAV: Constant angular velocity CLV: Constant linear velocity

Question 41

Explain delays fro optical disks

Answer 41

Worse, disk spins more slowly, seeds are slower, focus time on head DVD layer change time

Question 42

What makes SSD different

Answer 42

No mechenical parts, so these delays gone, no tracks

Question 43

SSD are complicated

Answer 43

Writing is complicated, cells cannot be overwritten, erased then written. SSD also have garbage collection (clean up fragmentation space )

Question 44

What are two main disk control standards

Answer 44

SCSI: Small Computer Systems Interface SATA: Serial ATA, Serial Advanced Technology Attachment

Question 45

What is the difference in SCSI and SATA

Answer 45

- SCSI traditionally outperforms ATA, processor for controller - SATA potentially surpasses SCSI on data transfer rates, possibly on overall performance, but uses more processor