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Arch, OS & Nets for Unix > Day Before Exam > Flashcards

Day Before Exam Flashcards

1
Q

ISA?

A

Instruction set architecture.

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2
Q

ISR?

A

Interrupt Service Routine.

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3
Q

DMA?

A

Direct Memory Access?

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4
Q

Three techiniques for I/O data exchange?

A

Programmed (CPU waiting), Interrupt Driven (avoids active polling - ie repeat checking), DMA (extra module)

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5
Q

Three types of DMA?

A

single bus, integrated with I/O, extra I/O bus.

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6
Q

PC?

A

Program Counter

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7
Q

IR?

A

Instruction Register

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8
Q

AC?

A

Accumulator Register.

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9
Q

DRAM and 3 points.

A

Dynamic RAM. Uses charges in capcitors. Information must be refreshed frequently due to charge leakages. Cheap. Used for main memory.

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10
Q

SRAM and 3 points.

A

Static RAM. Uses flip flops. Holds data as long as power supplied. expensive. Used for cache memory.

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11
Q

ROM and 2charachteristics

A

Read only memory. Non-volatile, so no power source required to keep data in memory. used to store BIOS which is required when computer turned on.

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12
Q

PROM

A

Programmable ROM (once only)

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13
Q

EPROM

A

Erasable programmable ROM. Expensive. Erase completely with Ultraviolet light.

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14
Q

EEPROM

A

Electrically erasable ROM. Erase partly.Very expensive.

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15
Q

Flash Memory characheristic

A

can be erased in seconds. High Density.

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16
Q

What is cache?

A

SRAM located between CPU and main memory. Purpose = increase I/O performance of cpu.

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17
Q

What is locality of reference?

A

Computer performance is improved by caches with efficient transfer strategies.

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18
Q

Cache replacement algorithms? 3

A

Least recently used, least frequently used, FIFO

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19
Q

Magnetic Disk - describe

A

Fast and large. Circular platter coated with magentisable material. Divided into rings called racks. Tracks seperated by inner gap and broken into sectors.

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20
Q

Access time of magnetic disk?

A

Is seek time (R/W head to correct track) and Rotational Latency (disk to spin to correct sector).

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21
Q

rpm of magentic drives?

A

5400rpm. 7200rpm available.

22
Q

How to increase capacity of magnetic drive?

A

Use more than one platter. Use both sides of platter.

23
Q

What does formating a magentic disk mean?

A

Make it usable for an OS. Control data used to mark tracks and sectors.

24
Q

RAID

A

Redundant Array of Independent Disks. Multiple disks in parallel. Extra reliability.

25
Q

What is a process?

A

a program being executed.

26
Q

Memory management - system requires it for 3 reasons

A

Sharing(several processes same memory), Relocation (prcoess returned to main memory at different location), Protection (between processes accessing each other)

27
Q

5 types of memory management:

A

Fixed partitioning, Dynamic partitioning, Paging, Demand Paging, Virtual Memory.

28
Q

Internal versus external fragmentation?

A

Internal = fixed partitioning wastage of space when process smaller than partition. External = dynamic partitioning space between partitions as processes swapped in and out.

29
Q

3 algorithms for dynamic partitioning placement?

A

best fit, first fit, next fit.

30
Q

4 charachteristics of paging:

A

Frames = partition memory. Pages = partition process. Page table = OS tracks frame locations for each page in process. Memory map = page number and offsets within page.

31
Q

What is demand paging?

A

Process does not have to be loaded in it’s entirety to memory. Page swapped in and out as needed.

32
Q

What does demand paging use?

A

Page interrupt handler to decide swapping of process pages from secondary to main memory.

33
Q

What does a process contain? 5

A

Stack, Memory, Heap, Data, Text.

34
Q

PCB?

A

Process Control Block

35
Q

Process Image consists of:

A

program data, program to be executed, stack, PCB

36
Q

Short Term Schedulers job:

A

Dispatcher, decides which job to exectue next. Frequent.

37
Q

Medium Schedulers job:

A

Swap processes between main memory and hard disk. Suspend and activate. Buffer between short and long.

38
Q

Long term schedulers job:

A

decides which process to admit. Infrequent.

39
Q

What are suspend queues?

A

Dispatcher uses them to prioritise processes.

40
Q

Starvation?

A

A process never getting to CPU. Mayeb because of less priority. Safeguard by changing priority queue based on ag and use more priority queues.

41
Q

List 5 scheduling algorithms:

A

FCFS, SPN (Shortest Process Next), SRT (shortest remaining time), RR (round robin), MLF (multi-level feedback).

42
Q

Describe RR

A

Round Robin: Pre-emption algorithm based on clock interrupt. next process chosen on FCFS basis. Best for CPU bound processes and interractive systems.

43
Q

Concurrency:

A

Apparent simultaneous execution of processes. Time Slicing CPU. Requires cooperatice processes to share CPU

44
Q

What is data incoherence?

A

Can occur if two processes share data and cause it to be inconsistent or incorrect.

45
Q

Three levels of awareness concurrent processes may have of one another:

A

UNaware - compete for rsources (MUtual exclusion, deadlock, starvation). Indirectly aware - share resources (ME, Deadlock, starvation, data incohernce), Directly aware, cooperate by communication (deadlock, starvation).

46
Q

What is deadlock

A

Permanent blocking of processes as they wait for each other. Only happens in concurrent system.

47
Q

Critical Section?

A

Part of the process that tries to use a critical resource. Only one process allowed to enter CS for a resource at a time. This is mutual exclusion.

48
Q

Mutual Exclusion? 5 points

A

1 process at a time. others processes must not interfere when they halt. no deadlock or starvation allowed. process in CS for a finite time. No delay to access of CS.

49
Q

two approaches to mutual exclusion:

A

Hardware (test and set). OS (semaphores).

50
Q

psudo code for semaphore approach

A

Process Pi: repeat Wait(s); CS Signal(s); RS forever. RS = remainder section.

Arch, OS & Nets for Unix (13 decks)

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