Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

operating systems > Final > Flashcards

Final Flashcards

1
Q

Explain What CPU Registers are

A

Fast memory units on the CPU
- split into two categories: control and status registers and user-visible registers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the Program Counter

A

A register which contains the address of the next instruction to be fetched

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the instruction Register?

A

Register containing instruction most recently fetched

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Explain the Basic Instruction Cycle

A
  1. CPU fetches next instruction from memory
  2. CPU executes instruction
  3. Program counter is consulted for next instruction and incremented
  4. CPU must wait for IO to complete
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain how Interrupts fit into the Instruction cycle

A

computers allow IO modules to interrupt the CPU. CPU checks for interrupts after each instruction
and if there are none fetches the next instruction from the current program. If an interrupt is found execution of program is suspended and interrupt handling is entered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Explain what an Interrupt Handler is

A

A program that determines the nature of the interrupt and responds accordingly. It then transfers control of the program back to the stored interrupt point of the program

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

List the 4 interrupt Classes

A

IO, Program exception, Timer, Hardware failure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain what happens with Multiple interrupts

A

further interrupts are disabled during an interrupt. Others remain pending until current interrupt is resolved. Interrupts have priority

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain the three possible Communication techniques for IO operation

A
  1. Programmed IO - no interrupts (cpu must wait), IO module preforms actions on processors behalf
  2. Interrupt-driven IO - CPU can execute code during IO operation: it gets interrupted when IO happens - no needless waiting but takes a lot of processor time watching for interrupts
  3. Direct memory access - block of data is transferred directly from memory without going through CPU
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain Cache memory

A

Small cache of expensive but extremely fast memory which interacts with larger slower memory. Cache is checked first to determine if info is present, if it is, info is used from cache. Otherwise, data is copied from main memory and temporarily stored in the cache

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Explain Access Time

A

Time to bring referenced word into the processor
Access time for cache (T1) + access time for main memory (T2)= total access time (T)
if word in cache T= T1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is an operating system and what are its goals?

A

An operating system is a program that acts as an intermediary between a user and the hardware by managing resources and conflicts
Goals:
- Execute user programs
- make the computer convenient
- use hardware efficiently

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the Kernel

A

The one program running at all times on the computer. It operates on a different layer than things the user can access and is responsible for providing secure access to machines hardware.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain the Computer System Structure

A

Can be divided into 4 components
Hardware - cpu, memory, IO devices
Operating System - controls and coordinates use of hardware
Application programs - define the ways system resources are used
Users

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain Storage structure

A

Main memory (RAM) - only large storage media CPU can directly access (volatile)
Secondary storage - extension of main memory that is non-volatile but can’t be directly accessed by CPU

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are priveleged Instructions?

A

Instructions that can only be executed in Kernel mode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the purpose of System Calls?

A

System calls allow user-level processes to request services of the operating system. system calls are
implemented using software interrupts. Realize that the OS is interrupt driven and that interrupts are received
both from the hardware and software as requests to perform some action.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Explain the two types of Multiprocessing

A

Asymmetric Multiprocessing - each processor is assigned a specific task but they are all running simultaneously
Symmetric - each processor performs all tasks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Explain Multi-programming

A

Multiprogramming organizes jobs so CPU always has one to execute. (a subset of total jobs kept in memory)
one job is selected and run. if a task has to wait on something (say an IO) OS switches to another job

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a Process?

A

A process is a program in execution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What activities in regards to process management is the OS responsible for?

A

-Creating and deleting processes
-suspending and resuming processes
-providing mechanisms for process synchronization and communication
-providing methods to handle deadlocks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

List the 5 Process states

A

new: process being created
running: instructions being executed
waiting: waiting for event
ready: waiting to be assigned to processor
terminated: finished executing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Explain the process control block (PCB)

A

Info associated with each process
- program counter - process state - Cpu registers - memory allocated to process - accounting info (cpu used, clock time elapsed) - IO devices allocated and open files

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Explain the purpose of process scheduling?

A

Maximizes CPU use by quickly switching processes onto the CPU for time sharing. The process scheduler selects next execution from available processes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the three scheduling queues?

A

Job queue - set of all processes
Ready queue - all processes residing in main memory (ready)
Device queues - set of all processes waiting for an IO device

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are the differences between the long-term scheduler (job scheduler), the short-term scheduler (CPU scheduler) and the medium-term scheduler?

A

LTS - selects which processes should be brought into the ready queue
- infrequent (seconds, mins) controls the degree of multiprogramming

MTS - can be added if degree of multiprogramming needs to decrease
- performs swapping: removes process from memory and stores it on disk, then brings it back to continue executing

STS - selects which process should be executed next and allocates CPU (milliseconds)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Explain the resource sharing options in Process creation

A
  1. Parents and child process share all resources
  2. Children share a subset of parents resources
  3. no resources are shared
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Explain the execution options with parents and child processes

A
  1. parents and children execute concurrently
  2. parents wait for children to terminate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Explain Process Termination

A

Process executes last statement and aks the OS to delete it. Process resources are deallocated by OS. Parent may terminate execution of child processes (if all children are terminated when the parent is it is called cascading termination)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Explain the Two models of Inter-process communication

A
  1. Shared memory
  2. Memory passing - processes use send(message) and receive(message) to share info.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the difference between indirect and direct communication in regards to processes?

A

Direct - processes name each other explicitly (send(P, message)), a link is established automatically and is associated with one pair of communicating processes (uni bidirectional)

Indirect - messages are directed and received from mailboxes, with each one having a unique id. processes can only communicate if they share a mailbox. a link can be associated with many processes and each pair of processes can share several links

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Explain How Synchronization works in IPC

A

message passed may be blocking or non-blocking. Blocking is considered synchronous

blocking send has the sender send a request to the receiver and block until it receives an acknowledgement, non-blocking is asynchronous and has the sender send the message and continue operation

blocking receive has the receiver wait idle until a send message is received. non-blocking has the receiver receive a valid message or null if there is no message yet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Explain and list the different types of buffering attached to process links

A

Queue of messages attached to the link
1. zero capacity - 0 messages can be held and sender must wait for receiver
2. Bounded capacity - finite length of n messages (sender must wait if link is full)
3. unbounded capacity - infinite length, sender never waits just sends

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is an Ordinary Pipe

A

Unidirectional relationships between processes where one end writes and sends what is written to the other end where the other process reads
requires parent-child relationship

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Explain the difference between named pipes and ordinary pipes

A

named pipes are like ordinary pipes but bidirectional and they do not require a parent child relationship

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Explain the difference between threads and Processes

A

A process is a program being executed via a thread with code, data and other resources. it owns memory, files and resources

A thread is a way of making a distinction between the resources and the executing process. A process is made up of threads so there can be multiple threads which share memory code and files

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Multicore programming

A

multi-core - multiple cores are placed on a single chip where each core appears as a separate CPU

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Explain what Concurrency is?

A

Supports more than one task making progress
With 1 processor a scheduler provides concurrency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Explain the different types of parallelism

A

Parallelism: implies a system can perform more than one task simultaneously

Data parallelism - distributes subsets of the same data across multiple computing cores and performing same operation on each core

Task parallelism - involves distributing data but not tasks (threads) across multiple computing cores - each thread performs a unique operation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is the difference between user and kernel threads

A

User threads - supported above kernel, kernel is unaware of them

Kernel threads - supported and managed directly by the OS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What are the three ways of establishing a relationship between user and kernel threads?

A

Many to one: many user to 1 kernel
many to many: many user to many kernel
one to one: 1 kernel to 1 user

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Explain what signal handling entails with respect to threads

A

Signal handler processes signals which notify a process when an event has occurs

signal is generated -> signal is delivered to process -> signal is handled by default handler or user defined one

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

The target thread is the thread to be cancelled. How is cancellation handled?

A

Asynchronous cancellation terminates target thread immediately.

Deferred cancellation allows the target thread to periodically check if it should be cancelled. - this method is employed because cancelling asynchronously can cause issues if a thread is cancelled in the midst of updating data
- A flag indicates whether it is safe to cancel

44
Q

Explain What the Short term (CPU) scheduler does

A

Schedules the next process, makes decisions when:
1. switches from running to waiting
2. switches from running to ready
3. switches from waiting to ready
4. when process terminates

45
Q

What is the difference between pre-emptive and non-preemptive scheduling?

A

Preemptive scheduling allows a running process to be interrupted by a high priority process, whereas in non-preemptive scheduling, any new process has to wait until the running process finishes its CPU cycle
- preemptive can cause starvation if a low priority process is butted by many high priority ones

46
Q

Explain the Scheduling criteria?

A

CPU utilization - keep cpu busy at all times

Throughput - # of processes that complete there execution/time (e.g. 5 seconds)

turnaround time - amount of time to execute particular process

waiting time - total time process in queue

response time - amount of time from when request was submitted until first response

47
Q

Explain the pros and cons of the first come first serve Scheduling algorithm

A
  • First come first serve
    convoy effect - short processes can be stuck behind long ones

Pros - simple and easy, costs little time to make scheduling decision

Cons - high waiting time, convoy effect causes poor CPU utilization

48
Q

Explain the pros and cons of Shortest-Job-First

A

Associate with each process the length of its next CPU burst and use the lengths to schedule the process with the shortest time

non-preemptive - once CPU given to the processes it can’t be preempted

preemptive - if a new process arrives with CPU burst length less than remaining time of current execution preempt - optimal

Pros - ensures low average waiting time
cons - can cause starvation

49
Q

Explain the pros and cons of Round Robin

A

each process gets a small unit of CPU time - after this time has elapsed the process is preempted and added to the end of the ready queue

Average waiting time under RR often longer

typically higher average turnaround then SJF but better response

50
Q

Explain the pros and cons of Priority Scheduling

A

priority integer associated with each process and CPU allocated to process with highest priority

preemptive and non-preemptive

SJF can be seen as priority scheduling where priority is the predicted CPU burst time

starvation still a problem

51
Q

What are the problems with Concurrency = Parallelism

A

Concurrency - multiple tasks which start, run and compete in overlapping time periods in no specific order

Parallelism - is about multiple tasks that run at the same time on a hardware with multiple computing resources

Concurrent processes often need to share data and resources. Results of actions performed by concurrent processes will then depend on the order in which their execution is interleaved (program can give different results each execution)

52
Q

What is the critical Selection Problem

A

Each process has a critical section segment of code where it may be changing variables or writing to file….

If one process is in critical section no others can be

53
Q

How does Peterson’s algorithm solve the CSP (critical selection problem)

A

Algorithmic software solution

2 process example, 2 processes share 2 variables
int turn; boolean flag[2]
flag array indicates if a process is ready to enter the critical section flag[i] = true implies that Pi is ready

54
Q

explain Atomic Access

A

All solutions to CSP are based on it

memory at a specific address can only be affected by one instruction at a time

55
Q

explain how hardware locks solve the CSP

A

Two types of special atomic hardware instructions
-test memory word and set value:
shared boolean variable lock, initizalized to false. Each process wishing to execute CS code. solution results in busy waiting
-swap contents of two memory words:
compares contents of a memory location with a given value and IFF they are same modifies the contents that memory location to the new given value

56
Q

Explain how mutex locks solve the CSP

A

Hardware solution

Mutex locks use an associated boolean variable available to indicate whether lock is available or not

57
Q

Explain how Semaphores Solve the CSP

A

Hardware solution

has more sophisticated ways of communication than mutex locks for processes to synchronize

uses an integer value instead of boolean

58
Q

What is a deadlock

A

When two processes try to go into the same nested critical section in a different order

like when two timid people come to a four way stop and neither starts up again until the other has gone

59
Q

Explain the conditions that create a deadlock

A
  1. mutual exclusion: only one process at a time can use a resource
  2. Hold and wait: a process holding resources is waiting to require additional resources held by other processes
  3. no preemption: a resource can be released only voluntarily by the process holding it upon its task completion
60
Q

What is a safe state?

A

Safe state = guarantee of no deadlock

Unsafe state = possibility of a deadlock, deadlock avoidance prevents it from entering

System is in a safe state if there is a sequence of all processes such that for each Pj, Pi can still be satisfied with currently available resources

61
Q

Explain What an avoidance algorithm does

A

It prevents the system from ever entering an unsafe state by knowing the future needs of any resource.

Single instance of resource type - use a resource-allocation graph

multiple instances - use bankers algorithm

62
Q

How does deadlock detection work?

A

Allows system to enter a deadlock state and recovers it. It uses a wait for graph (where only nodes are processes) and periodically checks if there is a cycle (cycle = deadlock). It requires n^2 operations where n is num of processes

63
Q

How does the system recover from a deadlock?

A

It aborts all deadlocked processes one at a time until the cycle is eliminated. Choosing order of elimination is done in many ways.

Resource Preemption - selects a victim to minimize cost and rollsback until a safe state and restarts the process from there. Can cause starvation where the same processes may always get picked as the victim

64
Q

What is the purpose of Base and Limit Registers?

A

They define the logical address space
-base register contains value of smallest physical address
-limit register contains range of logical addresses

Address >= base && Address < base+limit -> access memory
otherwise it is a trap

65
Q

What are the timings of address binding?

A

Programs on disk, ready to be brought into memory to execute form an input queue

Compile time: if memory location known prior

Load time: must generate relocatable code if mem location not known at compile time

Execution time: binding delayed until run time

66
Q

What is the difference between logical and physical address space?

A

Logical address - generated by the CPU
Physical address - the physical memory seen by the memory unit

67
Q

What is the MMU and what does it do?

A

Memory management unit is a hardware device that at run time maps virtual addresses to physical ones

e.g. value in relocation register (base register) is added to every address generated by a user process

68
Q

Explain dynamic linking

A

Static linking - when system libraries and program code combined by the loader into the binary program image

Dynamic linking - essentially shared libraries. static linking but postponed until execution, a small piece of code called the stub is used to locate the appropriate memory resident library routine

69
Q

What is swapping?

A

When a process is swapped temporarily out of memory to a backing store and then brought back into memory to continue execution

  • total physical memory space of processes can exceed physical memory
  • major part of swap time is transfer time
70
Q

Explain the two swapping methods

A

Backing store - fast disk large enough to accommodate copies of all memory images for all users; must provide direct access to those images

Roll out, roll in - swapping variant for priority based scheduling algorithms. lower priority process is swapped out so higher one can be executed

71
Q

What is context switch time including swapping?

A

if next process to be put on cpu not in memory it needs to be swapped out with another

100mb process with transfer rate of 50mb/sec
-> swap out and swap in time of 2000ms (4000ms total)

72
Q

What is a hole and how is it used?

A

A hole is a block of available memory

when a process arrives, it is allocated memory from a hole large enough to accommodate it

73
Q

What is the Dynamic storage-allocation problem?

A

It is the problem of how to satisfy a request of size n from a list of free holes

  • first-fit: allocate first hole big enough
  • best-fit: allocate smallest hole big enough
  • worst-fit: allocate largest hole
74
Q

Requirements a solution to CSP must satisfy

A

Mutual exclusion: only one process can be in the critical section at any moment of time
Progress: if some processes want to enter the CS and there is no process in the CS, eventually one of the processes will
enter the CS.
Bounded Waiting: (starvation free) a process waiting to enter the CS can be overtaken only finite number of times
before being give access to the CS

75
Q

Explain what fragmentation is and the two different types

A

When processes load and unload they fragment the available memory, leaving memory blocks too small to contain any processes and thus useless.

Internal fragmentation occurs when there is unused space within a memory block.

External fragmentation occurs when a storage medium, such as a hard disc or solid-state drive, has many small blocks of free space scattered throughout it.

76
Q

How do you reduce external fragmentation?

A

Compaction, shuffle memory around to place all free memory together in one large block. however this is only possible if memory relocation is dynamic

77
Q

What is segmentation?

A

A way of organizing processes in memory, a process is divided into segments.

It creates a segment table which maps a two-dimensional Logical address into a one-dimensional Physical address. It’s each table entry has:

Base Address: It contains the starting physical address where the segments reside in memory.
Segment Limit:  Also known as segment offset. It specifies the length of the segment.
78
Q

What does contiguous mean?

A

being in contact. two things are contiguous if they are touching on a boundary point

79
Q

What is paging?

A

A memory scheme which eliminates the need to contiguous allocation of physical memory. It divides physical memory into fixed sized blocks called frames. Logical memory is divided into same size blocks called pages. A page table translates logical memory to physical addresses

A list of free frames is kept

80
Q

How are pages located?

A

page number (p) - used as an index into a page table which contains base address of each page in a physical memory

page offset (d) - combined with base address to define exact address

p = m - n, d = n where logical address space = 2^m and page size 2^n

81
Q

Explain what Translation look-aside buffer (TLB) is

A

Page table kept in main memory, page-table base register points to page table and page-table length register indicates the size. This means 2 memory accesses necessary for every instruction

TLB’s solve this by directly storing page and frame number (Address space identifiers). like the cache if an address isnt in TLB it is loaded there form next time

82
Q

How is memory protection done with page tables?

A

Memory protection bit is associated with each frame to indicate if read-only or read-write is allowed

a valid-invalid bit is attached to each entry in the page table and indicates that associated page is in the processes logical address space

83
Q

Explain Hierarchical page tables

A

Page tables can get very large so it is hard to find contiguous space in main storage. The logical address space is broken into multiple page tables which point to each other

e.g. 2 level paging - 32 bit machine with a page number of 22 bits and offset 10 bits
can become p1 12 bits | p2 10 bits | d 10 bits

84
Q

What is an inverted page table

A

Doesn’t keep track of logical pages, but physical ones. It has one entry for each real page of memory

85
Q

What is partial loading?

A

Code needs to be in memory to execute but the entire program is rarely used. Partial loading is the ability to execute a partially loaded program

86
Q

What are the advantages of partial loading?

A

More processes can be maintained in memory since only parts are loaded. Memory won’t fill up on bloated unused parts of processes. CPU utilization is increased too since more processes in ready state

87
Q

What is virtual memory?

A

A storage allocation scheme in which secondary memory can be accessed as though it were apart of the main memory. Virtual addresses are mapped into physical addresses in memory.

88
Q

What is demand paging?

A

A continuation of virtual memory, it brings a page into memory only when it is needed by using swapping

page is needed -> reference to it
- invalid reference = abort
- not in memory = bring to memory

89
Q

What is the valid-invalid bit in regards to paging?

A

Each entry in a page table has a valid invalid bit where i = non-in memory v= in memory

90
Q

What is a page fault?

A

A page fault occurs when a program references a virtual memory page that is not currently resident in physical memory. This happens when the required page has been paged out to disk or has not been accessed yet. When a page fault occurs, the operating system handles it by fetching the required page from disk and updating the page tables to reflect the new mapping.

91
Q

What is copy-on-write?

A

An optimization which allows both parent and child processes to initially share the same pages in memory. It copies the pages if either process modifies them

92
Q

What is page replacement and why is it necessary?

A

Page replacement occurs when we are trying to bring a page into memory and there are no free frames. The computer finds a page in memory and swaps it with that one trying to find one to replace that will cause the least page faults

93
Q

List the three Page replacement algorithms and explain how they work

A

First in first out - OS maintains a queue of pages and first one in is first out

Optimal - replaces a page that wont be used for the longest period of time - impossible to determine and only used to evaluate other algs

Least Recently Used - time of last use is associated with each page and the least recently used one is replaced

94
Q

Explain the frame allocation schemes

A

Equal allocation - split m frames among n processes equally (100 frames 5 processes = 20frames/process)

Proportional allocation - allocate according to size
si = size of process pi
S = sum of all si
m = total number of frames
ai = allocation for pi = (si/S) * m

95
Q

What is the difference between global and local allocation?

A

Global replacement - process selects replacement from set of all frames. process execution time can vary greatly but it has a greater throughput

Local replacement - process selects only from its own frames. more consistent per-process performance but it can cause thrashing if there is not enough allocated frames

96
Q

What is thrashing?

A

Thrashing is when a process doesn’t have enough frames, which causes the page fault rate to be very high. A page fault occurs and a page is replaced because of it, then the replaced page is needed again so another page fault occurs

97
Q

What is a file?

A

A continuous logical address space with a type, attributes and operations

A file is typically viewed as a numbered sequence of blocks or records

98
Q

What is a directory and what structures can it have?

A
  • directory is a collection of nodes containing information about a file

Single level directory - each entry leads to a file

two-level directory - separate directory for each user -> user directory leads to single level directory

Tree-structured directory - root directory at the top with any number of subdirectories which can lead to files or other directories

Acyclic-Graph Directory

99
Q

Explain the Acyclic-Graph directory in detail

A
  • result of shared sub-directories and files

when a file is changed both people view even though the file can have different names to both

Link - pointer to an existing file or sub-directory to ensure file is found even if name is different

100
Q

List the Disk space allocation methods and explain them:

A

Contiguous allocation: each file occupies a set of contiguous blocks - normally best performance since its simple but it can be difficult to find space for files

Linked allocation: each file is a linked list of blocks -> locating a block could take many IO’s and efficiency can be improved by clustering blocks

Indexed allocation: each file has its own index blocks of pointers to its data blocks - extra space for index

101
Q

What is a bit map?

A

A bit map is a way of free space management

bit[i] = 1 -> block[i] is free
bit[i] = 0 -> block[i] is occupied

102
Q

What is a free list

A

A way of free space management

A linked list is used where a free block is linked to another…….. until the last free block

103
Q

How does an HDD work

A

like multiple record players stacked on top of each other. It has multiple disks stacked on top of each other and arms that read a part of the disk. The disks are divided into cylinders which the head reads

104
Q

Explain the disk structure

A

Disk drives are large 1-d arrays of logical blocks

1D array is mapped onto sectors of the disk sequentially - sector 0 is first sector of the first track on the outermost cylinder

105
Q

What is the Scan algorithm?

A

Alg for reading info from the disk

Disk arm starts at one end and moves towards the other servicing requests the whole way, when it reaches the end it does the same thing but back toward the start

106
Q

what is C-scan?

A

Like scan except instead of going to the end and then traversing back to the start, when the head reaches the end it travels back to the start without fulfilling requests.

107
Q

Explain Raid structure

A

Redundant array of inexpensive disks

they store redundant data by mirroring or storing a duplicate of each disk on another disk

operating systems (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions