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Year 10 (2022-23) > Computer Science (15.12.22) > Flashcards

Computer Science (15.12.22) Flashcards

1
Q

What are Analogue to Digital conversions?

A

-Analogue sound signals are continuous
-Digital sound signals are discrete
-Sound is digitised by repeatedly measuring and recording the sound wave

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2
Q

What are Convertors in Sound?-

A

-Sound must be converted into digital form in order to be stored and processed by a computer
-An Analogue to Digital Converter (ADC) is used to convert inputs to digital signals
-A Digital to Audio Converter (DAC) is used to convert digital signals to outputs

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3
Q

What is Sound Sampling?

A

-Sound is sampled using bit depth and sample rate
-SS is a measurement of the amplitude of a sound wave at a given time

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4
Q

What is the Sample Resolution?

A

-The number of bits (audio bit depth) used to record each measurement
-More bits used per sample enables the height of the wave to be more accurately measured but increases the file size
-Determines how closely the wave is sampled on the y-axis

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5
Q

What are Hertz?

A

-Sample rate is usually measures in Hertz (Hz)
-1 Hz = 1 sample per second
-Hz to KHz = divide by 1000

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6
Q

What is the Sampling Rate?

A

-The greater the frequency, the greater the accuracy, and the file size
-The number of samples taken per second

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7
Q

How do you Calculate the File Size?

A

-File size (bits) = sample rate x resolution x duration
-6 sample per second x 4-bit resolution x 3 seconds = 72 bits / 8 = 9 bytes

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8
Q

What is Lossy Compression - MP3?

A

-Removes sounds that we can’t easily hear or that least affect the playback quality
-It leaves out some data from the original so can negatively affect the sound quality
-Useful for storing, downloading or streaming

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9
Q

What is Lossless Compression? (sound)

A

-The formats are able to reduce the file size when compressed but do not lose any information
-FLAC (Free Lossless Audio Codes)
-ALAC (Apple Lossless Audio Codes)
-WMA (Window Media Audio)

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10
Q

What are other file formats?

A

-WAV and AIFF files are uncompressed audio files
-Lossy file formats are still very popular as they reduce the file size well
-MP3 (MPEG)
-AAC (Advanced Audio Coding) -> typically higher quality than MP3

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11
Q

What are examples of Bitmap image file formats?

A

-BMP
-JPG
-GIF
-PNG
-TIFF

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12
Q

What is an example of a Vector image file format?

A

-SVG
+editing softwares such as Illustrator (AI) and Photoshop (PS)

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13
Q

What is the bit depth of images?

A

more bits per pixel = more colour combinations
1 bit = 2 colours
2 bits = 4 colours
3 bits = 8 colour

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14
Q

What is BPI and Pixel?

A

BPI = beats per inch
Pixel = picture element

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15
Q

What are Bitmap (or Raster) Images?

A

-Made up of PICture ELement or pixels
-a pixel is the smallest identifiable area of an image
-a pixel’s colour can be changed by changing this value

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16
Q

What is the Image Resolution

A

-Resolution is the number of pixels in the image
-High definition (HD) television: 1920 x 1080 pixels

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17
Q

How do you create an image?

A

-Each pixel is given a binary value
-Each value represents a different colour
-Using one bit per pixel allows only 2 values, 0 and 1
1 = Black, 0 = White

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18
Q

How does increasing the image resolution affect the file size?

A

It increases the number of pixels in the image which would increase the file size

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19
Q

Two factors that affect the file size of a bitmap image:

A
  1. More pixels, it increases the file size
  2. More colours, more pixels needed-needs more file size
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20
Q

What is Serial Transmission? (USB)

A
  • Bits are sent one signal at a time over a single wire
    -Once the bit has been received, the next bit is sent
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21
Q

What is Parallel Transmission?

A

A number of wires are used so that many bits may be sent at the same time

22
Q

Parallel VS Serial Transmission:

A

If the same speed is used for one serial wire or eight parallel wires then parallel transmissions will be faster

23
Q

What is Lossless Image Compression?

A

-Will not lose any of the original data
-When data is uncompressed it is restored exactly as it was in the original

24
Q

What does RLE stand for?

A

RLE = Run Length Encoding
-uses frequency/ data pairs to encode each run length of the same coloured pixel

25
Q

What is RLE Frequency/Data Pairs?

A

-This is an uncompressed format where 1 = white and black = 0:
11110 11110 0000 0000 0000
It would be encoded as: 4 ‘1’, 1 ‘0’, 4 ‘1’, 16 ‘0’

26
Q

What are Parallel cables?

A

They are able to send more data than serial cables if the same data rate is used

27
Q

What is Crosstalk?

A

-May occur when a signal on one line creates a disturbance in another line
-This may a cause a bit to be reveresed in a parallel line
-longer cable= more chnce of crosstalk happening

28
Q

What is Skew?

A

-Each wire in a parallel cable has slightly different properties, signals arrive at a different time
-The receiver must wait until all lines are received until the next set of bits may be sent
-Transmission needs to be over very short distances to reduce the problem

29
Q

What are the USB features?

A

USB= Universal Serial Bus, is a serial cable that is commonly used to connect external devices to computers,laptops,table and smartphones
-The cable may be pluggled in or removed whilst the device is turned on

30
Q

Basics about compression:

A

1 MP3 = 4 floppy disks
data compression = trasmission
lossy -> lossees info. + smaller storage
lossless -> 2 main methods: RLE (most known), Hifman encoding (text)

31
Q

What is Simplex Transmission?

A

-Data travels in one direction only
-This would be used to send data from a keyboard to a computer

32
Q

What is Half-Duplex Transmission?

A

-Data is able to travel in both directions along a single connection, but can’t travel at the same time
-The full bandwidth is available to both the sender and receiver, can’t send at the same time

33
Q

What is Full-Duplex Transmission?

A

-Data is able to move in both directions simultaneously using 2 cables
-Ethernet network cables make use of 2 twister pairs of cable-one for sending and one for receiving
-Fibre optic cables use 2 fibres-one for transmitting and one for receiving

34
Q

What can cause a Transmission Errors?

A

-Electrical interface
-Power surges
-Synchronisation issues
-Wear and tear on the cable or connectors

35
Q

What can Transmission Errors cause?

A

-Data to be lost
-Data to be gained
-Data to be changed

36
Q

What is Error Checking?

A

-Computers need methods to check for data transmission errors caused by interference
-These methods include the use of:
-Parity bits
-Check digits
-Echo checks
-Automatic Repeat Requests (ARQ)

37
Q

What are Parity Bits?

A

-When sending a byte of data, one bit is used as a parity bit
-Used to check if there is an error in transmission
-Even parity-> total number of 1s transmitted are an even number

38
Q

How do you use Parity for Error Detection?

A

-When data is transmitted, the parity bit is set at the transmitting end and parity is checked at the receiving head
-Wrong number of bits found (doesn’t know which bit was incorrectly transmitted) = error has ocurred
-If a transmission error is found, the receiving device notifies the transmitting end and the data is resent

39
Q

How do you Check the Data Entries?

A

-Barcodes and other numbers have check digits which are used to make sure a number has been entered correctly
-A barcode scanner may misread the number and request it to be scanned again
-A checkout assitant or customer may mistype the number if they have to enter it manually

40
Q

What is a Check Digit?

A

last digit in barcode

41
Q

What is Encryption?

A

-the process of changing data into another form or code so that only people with access to a secret key or password can read it
-may not be written in readable form

42
Q

What is the Ceaser Cypher?

A

-A basic encryption algorithm where the alphabets are displaced by a known amount
eg: Caesar code wherein the letters are displaced by 5 places

43
Q

How does the Caesar Cipher work?

A

-The original message is called plaintext. The encrypt text is called ciphertext
-Only the sender and the receiver know the encryption key. Based on the encryption key, the scrambled message received is decrypted

44
Q

What is Decryption?

A

the process of converting the encrypted message to plaintext

45
Q

What are some disadvantages of CC?

A

-Can be easily cracked by unintended users
-Cannot be used for highly confidential info.

46
Q

What is the Reverse Cipher?

A

A message is encrypted in reverse cipher by reversing the message

47
Q

What is the Substitution Cipher?

A

Denotes encryption algorithms wherein each charcater is replaced by another character

48
Q

What is the Pigpen Cipher?

A

Alphabets are placed in grids and the characters are encrypted using the shape of the section of grid it represents

49
Q

What is Modulo 2 Encoding?

A

XOR operation: output is 1 only when both the inputs are different.

50
Q

What are Transposition Ciphers?

A

The plaintext is rearranged in a new order to form cipher text. Two method:
-Rail fence method
-Route method

Year 10 (2022-23) (24 decks)

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