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rest of 1.1.3 Flashcards

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1
Q

what is a drive

A
  • device that reads and writes data from secondary storage
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2
Q

what is media

A
  • what the data’s actually stored on
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3
Q

Explain the advantages and disadvantages of owning films that are streamed/downloaded on demand rather than owning physical copy

A

Advantages:
- access film anywhere, anytime with internet connection
- no physical storage needed
- no risk of film stolen/damaged
- optical drive not required to play film

Disadvantages:
- reliant on internet connection
- enough storage to download film reliant of 3rd party servers providing connection
- some prefer physical copy
- if company streaming film goes out of business, film lost

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4
Q

what are optical storage devices

A
  • optical drive and choice of media (CDr or CDrw, DVD-r or DVD-rw and Blu-Ray)
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5
Q

which media has the largest capacity of all optical storage devices

A
  • Blu-ray (designed to supersede DVD due to greatest storage capacity of all optical media)
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6
Q

what is CDr used for. And for what use is CDrw very good for (think about the difference between both, what can one do the other can’t)

A
  • store + distribute music
  • CDrw as backup option
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7
Q

why did DVD supersede CD and what are DVD’s used to store

A
  • DVDr can store motion pictures and movies,
  • DVD-rw more useful backup option due to greater storage than CD
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8
Q

give examples of magnetic media

A
  • hard disks + tapes
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9
Q

why are solid state drives gaining traction?

A
  • small, lightweight + very quick to access data, no noise
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10
Q

why are SSD’s and embedded MultiMediaCard (eMMC) replacing magnetic hard disks and optical discs.

A
  • since capacity on SSD increases and cost decreases
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11
Q

give examples of solid state storage devices

A
  • SSD, memory sticks, flash memory cards
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12
Q

what storage device would you use for this scenario: home computer storing OS and applications

A
  • high storage data capacity, access reasonably quick, reliable, low cost byte for byte due to significant data storage requirements
  • portability + durability less of a concern (device in fixed place)
    CHOICE = magnetic media (hard disk) or could install smaller solid state drive to make computer faster when accessing OS
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13
Q

what storage device would you use for this scenario: Travel agent backing up 800GB data

A
  • high data storage requirements, portable = ideal (take backup offsite), doesn’t need to be quick, fairly durable + as backup device needs to be reliable, medium cost solution.
  • Optical not sufficient (data capacity requirements), solid state (expensive given amount of storage needed)
  • CHOICE = magnetic media
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14
Q

what storage device would you use for this scenario: Distributing video game for console

A
  • optical (low cost, portable, durable, reliable, capacity low = problem for graphic intensive games (only get 4.7GB on DVD), doesn’t need to be fast as consoles install software off the optical device onto own hard drive
  • cloud storage (game streamed and directly downloaded to hard drive after purchased)
  • overall depends on game capacity and cost
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15
Q

what storage device would you use for this scenario: Storing tracks on portable MP3 player.

A
  • These first 4 characteristics outweigh all other considerations in this scenario: portable, access files quickly, durable ,reliable + low cost ideal
  • CHOICE = solid-state storage (more expensive byte for byte though)
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16
Q

what is flash memory/SSD also used for other than just normal secondary storage

A
  • put OS or user configurable part of BIOS on SSD = improve time taken for system to execute boot sequence.
  • applications + data that are accessed frequently
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17
Q

what is secondary storage

A
  • applies to wide range of devices that provide reliable + persistent storage for data files + applications –> files not lost / easily corrupted.
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18
Q

what are some characteristics of secondary storage (include factors that should be considered when choosing secondary storage device)

A
  • non-volatile (data not lost when power removed)
  • high capacity, low cost, fast enough for loading and saving files
  • may be installed internally or externally.
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19
Q

give example of what external secondary storage devices primarily used for

A
  • transfer files from one computer to another or where it is not possible to upgrade internal storage.
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20
Q

rank solid state, magnetic and optical based on reliability

A

1.Solid state
2. Magnetic (mechanical parts can get damaged)
3. Optical (easy to scratch)

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21
Q

rank solid state, magnetic and optical based on speed

A

1.Solid state (quickest access speed due to no moving parts)
2. Magnetic
3. Optical

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22
Q

rank solid state, magnetic and optical based on portability

A

1.Solid state (easiest)
2. Optical (thin, lightweight and portable)
3. Magnetic (tend to be internal)

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23
Q

rank solid state, magnetic and optical based on power

A

1.Solid state (use less power and less heat/noise generated)
2. Optical
3. Magnetic (uses more power and more heat generated)

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24
Q

rank solid state, magnetic and optical based on durability

A

1.Solid state
2. Magnetic (mechanical parts eventually fail)
3. Optical (prone to damage)

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25
Q

rank solid state, magnetic and optical based on cost

A

1.Optical
2. Magnetic
3. Solid state

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26
Q

rank solid state, magnetic and optical based on capacity

A

1.Magnetic
2. Solid state
3. Optical

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27
Q

other than the factors previously mentioned, give a positive and drawback from solid state storage

A

+ no need to defragment
- limited number of read/write cycles

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28
Q

what is magnetic storage (what does hard disk have allowing it to read data and how is this data stored - MAGNET(north and south polarity = magnetised or not magnetised)

A
  • usually comprise of 1 or more metal platters with magnetic coating, each being double sided.
  • num platters = total storage capacity
  • Hard disks have a drive head that moves over surface of disk (there’s a slight gap to reduce friction –> wear and tear)
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29
Q

what is each platter broken down into

A
  • set of concentric (parallel) tracks
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30
Q

what are the tracks further broken down into

A
  • sectors
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31
Q

what is a cluster (or block/allocation unit)

A

a contiguous group of sectors

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32
Q

what are the principles of operations for hard disks

A
  • Binary data stored on platters as a series of polarised states (0 or 1)
  • To read and write data, device has two mechanical arms, 1 for each side of each platter. At the end of the arm is a read-write head with tiny magnet.
  • The platters spin + head sweeps across tracks, while sectors pass underneath the head as disk rotates
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33
Q

what is the advantage of the fact that the platters spin and head sweeps across tracks while sectors pass underneath the head as disk rotates? Outline how this differs from magnetic tapes.

A
  • any block can be accessed directly without having to read through entire contents of disk.
    -This differs from magnetic tapes (the form of magnetic storage that disks replaced), which only allow serial access.
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34
Q

how is data represented in magnetic storage

A
  • on disk surface (a metal platter) by magnetised dots. - Binary data is represented through the two states of ‘magnetised’ and ‘not-magnetised’.
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35
Q

give pros of magnetic storage

A
  • high capacity
  • somewhat cheap
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36
Q

give cons of magnetic storage

A
  • Since it’s a mechanical component, it will eventually fail
  • Only read and written sequentially from start to finish —> impacted how data can be stored on these devices
  • becomes fragmented
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37
Q

what is a crucial factor in measuring rate of data access for magnetic disks.

A
  • Speed of rotation (Faster disk spins –> quicker data is retrieved.
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38
Q

why can read-write access speeds be varied for different HDD’s

A
  • The variation is determined by a range of factors, including how disk has been configured, size of the file + how fragmented the disk / file is. 
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39
Q

where is magnetic storage mainly used

A

backup centres
personal computers
mainframes

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40
Q

how does fragmentation of files occur.

A
  • when there is insufficient contiguous space to store the file.
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41
Q

what happens if a file becomes fragmented and how is the files read (include use of links to follow file segments)

A
  • If file fragmented, each part of file will be in separate location with link to next location. File read by following links until an end-of-file marker is reached.
  • If disk is nearly full, it will take longer to find space to write file segments + access a file that is spread across several locations.
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42
Q

describe how defragmenting a hard disk drive could improve performance of a computer

A
  • reduces movement of read/write head over hard disk which speeds up file access
  • this also reduces time taken to find files as they are stored contiguously on disk
  • writing onto disk would also be faster as it doesn’t have to find space to store file contiguously
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43
Q

how does solid state storage work

A
  • Work by a flow of electricity, forcing electrons into floating gates between 2 oxide layers + this causes change in charge in floating gate which can be measured as 0 or 1
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44
Q

what are solid state storage disks made up of

A
  • made up of a controller + bank of millions of NAND ‘flash’ memory cells each, having a floating gate transistor to allow electrical charge to be trapped.
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45
Q

what binary value represents a charged and uncharged cell

A
  • charged cell represents 0 - uncharged represents 1
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46
Q

over time, what happens to the oxide layers

A
  • oxide layers can deteriorate. eventually transfer of elections will become unreliable —> this media has finite number of read write cycles —> limited lifespan
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47
Q

fill the blanks: NAND flash cells are organised in terms of _____ (cell within a grid) and _______ (each row of cells)

A
  • pages
  • blocks
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48
Q

how is data read and written in SSD

A
  • Data read from an SSD by page, and written a page at a time, as long as surrounding cells are empty.
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49
Q

SSD: what happens if file is to be updated (hint: filling up SSD’s makes them perform slower so what action can cause slowing in performance)

A
  • cannot be done in original place.
  • The relevant block containing the pages must be copied to main memory + updated. It will then be written to a new area of the disk and the original block(s) will be erased.
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50
Q

what are suitable uses of solid state storage

A

Suitable for storing files that are read and changed frequently

51
Q

what is the common secondary storage combination for most computers

A
  • both magnetic + solid-state disks.
  • SSD as additional drive = sensible upgrade. it can store OS + files (including applications) used frequently.
  • Files (including applications) used less frequently can be stored on larger magnetic disk.
52
Q

give examples of optical drive and choice of media. outline what they can be used for

A

family of disc types including:
- CD-R/RW (music + archives)
- DVD-R/RW (films)
- Blu-Ray

53
Q

how do read only optical drives work

A
  • surface of disc burned by laser (makes it read only)
  • this creates pits and lands to store binary. the point where these pits and lands start/end causes light to scatter (reflected less). This change in reflectiveness read by light sensor (optoelectronic device) + interpreted as binary bits
54
Q

describe how optical drives can be writable

A
  • chemical composition (dye) of disc can be changed by reversible chemical reaction –> data can be erased and new data written
55
Q

how is the disc arranged

A
  • continuous tracks of data arranged in spirals
56
Q

fill the gaps: data is read __________ as disc rotates at varying speeds (________ near centre)

A
  • serially
  • faster
57
Q

how does writing to a disc work

A
  • laser in optical disc drive used at higher intensity than reading which burns tiny dots into chemical layer to alter amount of light reflected creating a readable surface representing binary.
58
Q

what is CD-ROM and DVD-ROM?

A
  • disc which can be read only. Manufacturer writes initial data which cannot be changed.
59
Q

where is CD-ROM and DVD-ROM used?

A
  • content distribution so that people can’t accidentally overwrite contents.
  • used to distribute films + music, deliver application software (light, portable + small physical space).
60
Q

what does the “R” stand for in CD-R and DVD-R?

A
  • ‘R’ = ‘recordable’
61
Q

what are CD-R and DVD-R known as?

A
  • ‘WORM’ (‘write-once read-many’) discs.
62
Q

what were CD-R and DVD-R known for being used for?

A
  • archiving data as it made a permanent copy which requires storage medium that can’t be overwritten.
63
Q

what does the “RW” stand for in CD-RW and DVD-RW?

A

‘RW’ = ‘rewritable’.

64
Q

what are CD-RW and DVD-RW known for being used for?

A
  • backing up (making temporary copy) computer files. This requires storage medium that can be overwritten
65
Q

how is longevity decreased for all types of disc

A
  • exposure to heat can cause polycarbonate and/or metallic layers to warp.
  • Any chemical layer can degrade over time (dye susceptible to light damage + extended exposure affects it —> degrades layer so increases chance of data being misread)
  • availability of drives to read them is diminishing
66
Q

When a computer system first receives power, no instructions are loaded in CPU and no external hardware is recognised. The system needs to load OS, which is stored on permanent secondary storage - hard drive, so it can start functioning. What is the solution to this problem

A
  • Solution = ROM (contains bootstrap - the set of initial start up instructions placed on it during manufacturing)
67
Q

what is RAM?

A
  • Temporarily stores data + instructions currently being processed
  • designed specifically for this purpose: fast read/write speeds, it’s addressable meaning storage locations have unique memory addresses + can be accessed directly by processor
  • RAM holds OS when computer is running
68
Q

what does RAM consist of

A
  • RAM consists of a number of memory locations used to store data or instructions in form of bit patterns.
69
Q

In order for a program to be executed, it must first be loaded into
1. where
and
2. where from
3. Explain why

A
  • it must first be loaded into RAM from Secondary storage
  • This is because RAM has quicker read + write speeds than secondary storage devices. The processor will fetch instructions (and any necessary data) from RAM directly before decoding + executing.
70
Q

why is RAM called Random Access Memory

A

Any of the locations in RAM can be accessed in same amount of time, unlike other storage devices where sensor I.e. read/write head needs to be moved into place. This is why RAM = random access: any location can be accessed “at random” with no impact on speed.

71
Q

compare RAM’s capacity to all of main memory

A
  • largest capacity
72
Q

give some disadvantages of RAM

A

Disadvantages: expensive, volatile + lower capacity than secondary storage devices.

73
Q

1.What is ROM
2. what system can it be used for and why

A
  1. Contains very first instructions for the computer (bootstrap)
  2. used for embedded systems (ROM cheaper as it has one function and needing to write to memory isn’t needed)
74
Q

some instructions and data are pre-built into ROM chips. what does this mean and why can it be useful (relate to storing what and use in what type of system)

A
  • can’t be over-written with electrical current so it’s read-only.
  • It’s useful for storing first instructions computer needs to boot up that don’t change and the use in embedded systems that have a dedicated purpose.
75
Q

what is the bootstrap

A
  • performs POST which sends signals to all connected components and make CPU aware of their existence, checking hardware is installed correctly, loads BIOS stored on ROM and sends it to RAM
76
Q

what is BIOS

A
  • BIOS = limited sequence of instructions that checks that core components of computer system (RAM, fundamental input/output devices, secondary storage) are connected and responding correctly.
77
Q

What happens once BIOS done

A
  • Once BIOS done, boot sequence loads essential parts of OS from secondary storage into RAM. From here, OS will oversee operation of computer, managing memory, storage, and requests for input/output.
78
Q

List some characteristics of ROM

A
  • located on motherboard
  • non-volatile (contents of ROM set by computer manufacturer)
  • smaller capacity than RAM
79
Q

What is software stored on ROM called

A
  • firmware
80
Q

what is cache and why is it faster than RAM

A
  • volatile (memory is erased when power is removed) fast storage which stores frequently used data and instructions
  • this means data transferred faster –> faster processing –> faster fetching data –> faster for cpu to access frequently used data from cache rather than CPU fetching data from RAM
81
Q

describe capacity and cost of cache compared to RAM

A
  • Cache smaller capacity + more expensive than RAM
82
Q

what are the different levels of cache

A
  • L1: quickest access speed but lowest capacity (part of processor itself)
  • L2 and L3: slowest but has more capacity. Closer cache is to CPU, faster it can read + write data but less stored
83
Q

Fill the gaps:

In a _______- ____ processor, each CPU core will have its own level ___ cache but might share levels two and three with the other _____ in the __________.

A
  1. multi-core
  2. one
  3. cores
  4. processor
84
Q

what are registers

A
  • they are onboard CPU and are very small memory devices which provide faster access than both RAM + cache but only hold few bytes most.
85
Q

registers are split into what 2 categories

A
  • general + dedicated / special purpose
86
Q

what are general purpose registers and how does this differ from dedicated purpose ones

A
  • General purpose registers used to temporarily store values generated by instructions, if they need to be used again in next instruction. Number of general purpose registers differs between models of CPU.
  • Dedicated registers serve specific purpose in FDE cycle.
87
Q

what is virtual memory

A
  • way a computer system can compensate for shortage of RAM. uses secondary storage to store apps and files currently open
88
Q

why is virtual memory used

A

Modern applications have high main memory requirements.
Running such applications on systems with minimal main memory will lead to issues as applications compete with each other for access to RAM –> slowdown in performance/lag.

89
Q
  1. In extreme cases what can very small RAM / multiple applications running cause to happen
  2. how to reduce likelihood of this happening
A
  1. system freeze / crash.
  2. computer systems allocate portion of secondary storage as VM for storage of applications and files currently open.
90
Q

why can using SSD’s be advantageous but also disadvantageous over HDD for VM

A
  • SSDs advantageous over HDDs –> access speed is closer to that of RAM.
  • Disadvantageous –> system using SSDs regularly for virtual memory reduces lifespan of it and therefore their finite read/write lifecycle.
91
Q

what does the OS do when system requires virtual memory

A
  • When system requires virtual memory, OS creates set of virtual addresses (RAM is separated into a set of physical addresses).
92
Q

data moved to virtual memory is stored as what

A
  • Data moved to virtual memory is stored as pages.
93
Q

what happens when CPU is ready to accept instructions from files in virtual memory

A
  • When CPU is ready to accept instructions from files in virtual memory, it moves the page files into RAM, allocating a physical address to the data.

(When page files are moved from VM to main memory, other data is moved from RAM to either VM or back to secondary storage)

94
Q

what is flash memory

A
  • non-volatile
  • uses special type of ROM that can overwritten
  • expensive but can be read from and written to at high speeds (no moving parts and low power consumption)
95
Q

fill the blanks:

  • Some ________________ use memory chip to store instructions (______ memory).
A
  • Some microcontrollers use memory chip to store instructions (flash memory).
96
Q

why is flash memory used as storage + main memory of microcontrollers and microprocessors

A
  • Microcontroller and microprocessors used to perform very specific task + often have only single program to run.
  • These programs can be stored + fetched from same place as there is no need for multiple programs to share same main memory, which would require one of them to be removed to make room.
97
Q

what is the difference between Microprocessor and Microcontroller

A
  • Microprocessor only consists of Central Processing Unit
  • whereas Microcontroller has memory, a CPU and I/O.
98
Q

what is the basic building block of RAM and what can it store

A
  • basic building block of RAM = memory cell which can store single binary digit.
99
Q

what is a group of memory cells called

A
  • Group of cells = memory location .
100
Q

what actually happens when a processor needs to read a memory location

A

processor can  read  memory location, i.e.
- load contents of that memory location to one of its registers (contents copied over and remain unchanged to that memory location)

101
Q

what actually happens when a processor needs to write to memory location

A

processor can write to a memory location, i.e.
- store the contents of one of its registers to that memory location (contents of that memory location are overwritten)

102
Q

RAM maximum capacity is defined by width of what

A
  • width of the address bus.
103
Q

what is DRAM. And what is it commonly used for and why

A

Dynamic Random Access Memory)
- This type of random-access semiconductor memory commonly used for a computer’s main memory –> cheap to manufacture.

104
Q

what are DRAM memory cells usually made up of

A
  • DRAM memory cells usually made up of capacitor and transistor.
105
Q

what does transistor and capacitor in DRAM memory cell store

(hint: transistor = transition / turn on or off. capacitor = charge)

A
  • capacitor in cell will store a charge (represents a single bit value). charged capacitor represents 0 + discharged capacitor represents 1.
  • transistor in cell will act as a switch to set / change value.
106
Q

what will happen to the storage of charge on a capacitor over time

A
  • charge on a capacitor will leak over time so system will need frequent memory refresh to restore capacitors to original charge.
    (This happens constantly in background –> not evident to user)
107
Q

what does SRAM stand for and what circuitry does it use

A

Static Random Access Memory which uses different type of circuitry (flip-flops).
(They don’t need to be refreshed.)

108
Q

is SRAM x2 faster or slower to access than DRAM.
does this mean its cheaper or more expensive

A
  • SRAM = twice as fast to access (read or write) as DRAM –> more expensive to manufacture
  • used for areas where speed = most important I.e. registers + cache memory.
109
Q

what areas is SRAM used for

A
  • used for areas where speed = most important I.e. registers + cache memory.
110
Q

what is a similarity between DRAM and SRAM

A

DRAM + SRAM = types of volatile memory (require constant power supply to maintain memory charge)

111
Q

what is PROM (programmable read-only memory)

A
  • type of ROM that‘s blank when manufactured and required data can be written to circuit by supplier of device only once with special tool known as programmer/burning the PROM
112
Q

what is PROM (programmable read-only memory) used for

A

used in microcontrollers, games consoles, mobile phones, and RFID tags

113
Q

what is EPROM (erasable programmable read-only memory)

A

EPROM can be rewritten many times. If contents of ROM need to be changed, memory unit removed from system before being erased and reprogrammed

114
Q

how is data erased from EPROM (erasable programmable read-only memory)

A

erasing data requires a special tool that emits a certain frequency of UV light. All contents erased in single operation (needs special equipment + operator expertise)

115
Q

what is EEPROM (electrically erasable programmable read-only memory)

A
  • EPROM technology superseded by EEPROM
  • Chip doesn’t have to be removed to be rewritten and entire chip doesn’t have to be erased to change specific portion of it as individual bytes can be erased electronically + device then reprogrammed

(Changing contents doesn’t require specialist equipment)

116
Q

what uses EEPROM (electrically erasable programmable read-only memory)

A
  • smart cards and remote keyless systems
  • But, some EEPROM devices have additional security features to protect device from hackers who may wish to attempt to reprogram it.
117
Q

what is virtual storage

A
  • Concept of storing + retrieving data over internet on cloud instead of local storage device (storage appears to be local but is physically located elsewhere)
  • can refer to abstraction/separation of logical storage from physical storage i.e. single structured storage area under a single drive which has folders + files can be stored across different media.
118
Q

what is Cloud storage 

A
  • facilitated by the internet. it’s an extension of client-server network where user files are stored centrally on a remote server maintained by 3rd party (this allows for centralised backups)
119
Q

Cloud storage can be configured so that it automatically synchronises with local drives. What does this mean

A
  • This means that there is always a local copy, in case there is no available internet connection.
  • Any changes made locally will be synchronised when connection next available.
120
Q

Advantages of cloud storage

A
  • data can be accessed at any time from anywhere on any device as long as there’s internet connection.
  • Data can be easily shared without need for removable media transfer.
  • Easier to collaborate + storage considered “limitless” (large capacity available for user),
  • easy to increase storage capacity
  • centralised backups = responsibility of third party provider, no need to purchase expensive hardware to store data
121
Q

Disadvantages of cloud storage

A
  • subscription fees may be expensive
  • if connectivity is poor, access times can be slow
  • dependent on internet connection
  • security of files more at risk
  • if service = down then access to files lost
122
Q

what is Network attached storage (NAS) 

A
  • provided in the form of dedicated stand-alone device that is installed as part of a LAN.
  • small NAS devices for home networks + larger for business use.
123
Q

When NAS is used, what will user see

A
  • When NAS is used, user will see drive listed alongside their local storage.
    (They don’t need to be aware of its physical location, but will lose access in event of network or device failure)

computer science ocr a level (15 decks)

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