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AIT 542 > Final > Flashcards

Final Flashcards

1
Q

What does STS stand for

A

Short term scheduler

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2
Q

What does STS users care about

A
  • Response Time
  • Turnaround time
  • Predictability
  • Deadlines
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3
Q

What does STS systems care about

A
  • Throughput
  • CPU Utilization
  • Fairness
  • Priority
  • Balancing Resources
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4
Q

What are two ways that STS processes decisions

A

– 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)

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5
Q

What polices can STS operate under

A
  • First come, first served (FIFO)
  • Round Robin
  • Virtual Round Robin
  • Shortest job first
  • Shortest remaining time
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6
Q

What are the three types of message passing

A
  • 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
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7
Q

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

A

Direct Addressing: Targeted, must know them.

Indirect addressing: Mailboxes, use common data structure

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8
Q

New class of scheduling for urgent processing

A

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

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9
Q

Name the 7 layers in OSI

A 
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
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10
Q

What communicates on each layer of the OSI model?

A 
Application: web applications
Presentation: http
Session: 80
Transport: TCP
Network: IP/packets
Data Link: Ethernet/frames
Physical: Cat5
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11
Q

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

A

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

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12
Q

Two types of real time scheduling deadlines

A

Hard real-time (must)

Soft real-time (should)

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13
Q

Real time system scheduling must by

A

preemptive and priority based

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14
Q

Real time scheduling must work in the following model for scheduling

A

Real time operating systems

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15
Q

What is deadlock

A

2 processes each waiting for the other to release a resource

-May be hardware or software

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16
Q

Why does deadlock occur?

A

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

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17
Q

What is deadlock versus starvation

A

-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.

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18
Q

What are the conditions for deadlock

A
  • 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)
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19
Q

How can we prevent deadlock?

A

Prevention
Detection
Avoidance

20
Q

What do we currently do to prevent deadlock

A

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

21
Q

Sequence of early programming

A 
Op Codes (numbers only)
Assembly Language (names for program, like add, mov, cmp)
22
Q

What were the early program for translation

A

Translator: called assembler

Language called: Assembly Language

23
Q

High level languages

A

Java, C, C++, Python…

24
Q

What is software engineering

A

discipline devoted to best practices in design and

building of programs

25
Q

Programming practies

A
  • Write code easy to read
  • Write code clear and easy to undertsand
  • Comment code
  • Write human readable form
26
Q

What is the compiler

A

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.

27
Q

What is the interpreter

A

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

28
Q

What is the assembler

A

Translates assembly language into machine (object) code.

29
Q

What is the loader

A

loads load modules into memory:

30
Q

What is the load module

A

Program that exist as a disk file, contains executable code

31
Q

What is the linker

A

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

32
Q

What are the different kinds of load modules

A

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

33
Q

What are two types of linking

A

Static and Dynamic

34
Q

How do you get code into memory:

A 
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).
35
Q

How much does a sector hold

A

typically 512 bytes

36
Q

How many sectors per track

A

63 on a hard disk

37
Q

What is the difference between track and sector

A

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

38
Q

Cylinder-Head-Sector calc

A

cylinderheadsector * bytes per sector

i.e. 6296 * 16 * 63 * 512 bytes per sector

39
Q

Average seek time per disk

A

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

40
Q

Explain difference between CAV vs CLV

A

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

41
Q

Explain delays fro optical disks

A

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

42
Q

What makes SSD different

A

No mechenical parts, so these delays gone, no tracks

43
Q

SSD are complicated

A

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

44
Q

What are two main disk control standards

A

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

45
Q

What is the difference in SCSI and SATA

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

AIT 542 (4 decks)

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