Chapter 1 - Information representation and multimedia (AS + A2)

Question 1

test your knowledge from IGCSE CompSci with this question:

what are the column weightings for an 8-bit binary number system?

(hint: think powers of 2)

Answer 1

(from heaviest to lightest) 128, 64, 32, 16, 8, 4, 2, 1

Question 2

attempt converting this binary number into denary:

11010010

(hint: add up the weightings of the 1-columns from left to right)

Answer 2

210

(from the sum of 128, 64, 16, and 2 - they were the turned-on bits here)

Question 3

attempt converting this denary number into binary:

239

(hint: try denary-subtracting 128 from this number first)

Answer 3

111001111

(from the difference of 239-128-64-32-8-4-2-1)

Question 4

use two’s-complement on this binary number:

01010111

(hint: first invert the number and then add a 1 to the rightmost bit)

Answer 4

10101000 -> 10101001

(the leftmost bit = -128 so the denary equivalent of this number = -87)

Question 5

add these two binary numbers without converting them into denary:

01011111
00010000

(hint: two’s complement is used here so the leftmost bit = -128)

Answer 5

01101111

(there’s a 1+1 in the bit equivalent to 32 so a carry should occur)

Question 6

subtract these two binary numbers without converting them into denary:

01100001
00010001

(hint: two’s complement is used here so invert the second number first)

Answer 6

01010000

(NB: any additional bits from a binary subtraction should be ignored)

Question 7

list the first 3 memory superunit names with their sizes under this:

the SI system

(hint: think powers of 10)

Answer 7

KB (one thousand), MB (one million), GB (one billion), etc.

(NB: the SI system’s suitable for some storage devices but is less accurate - more on the next system after this card)

Question 8

list the first 3 memory superunit names with their sizes under this:

the IEC system

(hint: think powers of 2)

Answer 8

KiB (2 to the power of 10), MiB (2 to the power of 20), GiB (2 to the power of 30), etc.

(NB: the IEC system’s accuracy makes it best for measuring RAM sizes!)

Question 9

try this question out:

what are the column weightings for a 16-bit hexadecimal system?

(hint: think powers of 16)

Answer 9

(from heaviest to lightest) 4096, 256, 16, 1

Question 10

try this question out:

what are the six hexadecimal letters used to represent digits larger than 9?

Answer 10

(from smallest to largest) A, B, C, D, E, F

Question 11

convert this binary number into hexadecimal:

101101010001

(hint: try splitting the number into 4-bit nibbles first)

Answer 11

B51

(1011 = 11/B, 0101 = 5, 0001 = 1)

Question 12

convert this hexadecimal number into denary:

B1A4

(hint: convert each individual digit into binary nibbles first)

Answer 12

45476

(Bx16(3)=45056, 1x16(2)=256, Ax16(1)=160, 4x16(0)=4)

(NB: two’s complement isn’t used here so the MSB’s a positive number)

Question 13

make a list of three things that the following can be used in:

hexadecimal numbers

Answer 13

1. memory dumps
2. HTML color codes
3. error messages

Question 14

try this question out:

what are the 4-bit codes used as digit representatives in BCDs (binary-coded decimals)?

(hint: use 4-bit binary register tables to help with your answer)

Answer 14

1. 0000 (0)
2. 0001 (1)
3. 0010 (2)
4. 0011 (3)
5. 0100 (4)
6. 0101 (5)
7. 0110 (6)
8. 0111 (7)
9. 1000 (8)
10. 1001 (9)

Question 15

add these two fixed-point BCDs up:

0000.0101 1001
0000.0100 0110

(hint: add 0110 if you spot a result that doesn’t look like a BCD digit)

Answer 15

0001.0000 0101

(1111 doesn’t fit into a BCD and adding 0110 to it should carry bits)

Question 16

state the operation that should be done on an ASCII code for this:

switching between uppercase and lowercase letters

(hint: standard ASCII uses 7-bit codes whereas extended uses 8-bit ones)

Answer 16

toggling the sixth bit to the left on/off

Question 17

list the advantages of the following over ASCII tables:

the Unicode standard

(hint: Unicode uses 16/32-bit codes)

Answer 17

1. unambiguous standardization
2. more efficient to code in
3. permits for private-use code assignments

Question 18

try this question out:

how many bits/pixel are needed for a raster image to be:
1. a monochrome image?
2. a 256-color image?
3. a true-color image?

(hint: think powers of 2)

Answer 18

1. a single bit for a monochrome image
2. 8 bits for a 256-color image (the minimum for multicolored images)
3. 24 bits/3 bytes for a true-color image w/ ~1M colors

(NB: varied intensities of red, green, and blue can create different colors in 8-bit/pixel images)

Question 19

consider a major impact of the following on raster image quality:

pixel density and resolution

(hint: try scaling a JPEG/PNG image up and down yourself)

Answer 19

blurrier results when scaling raster images up due to pixels being spread across a larger area

Question 20

consider a major impact of the following on raster image size:

resolution and bit depth

(hint: consider that image resolution and bit depth are both numbers)

Answer 20

the more you increase any/both of them the more space an image file takes up

(this can be proven by the file size = res * bit depth equation)

Question 21

calculate the file size of an image with the following properties:

• resolution: 720p x 480p
• bit depth: 24

(hint: file size = resolution * bit depth)

Answer 21

(720 x 480) x 24 = 8294400 B

(≈ 8.3 MB/7.91 MiB)

Question 22

list the advantages of the following over raster/bitmap images:

vector graphics

(hint: this sorta image uses geometrical calculations)

Answer 22

1. scalable w/o any noticeable loss in quality
2. space-savers due to their geometric nature

(all this makes vectors less realistic than bitmaps/rasters though)

Question 23

list the steps in the process of converting the following into digital:

analog sound waves

(hint: they need to go thru an ADC first)

Answer 23

1. removing frequencies outside the normal human hearing range of 20-20000 Hz
2. imprecisely sampling sound waves w/ their amplitudes at a given rate and resolution

(NB: sampling sound waves more frequently + at higher resolutions makes the resulting digital audio file larger - more on that after this flashcard)

Question 24

list all the pros and cons of doing the following with recorded sound:

more frequent sampling at higher resolutions

(hint: think back to the flashcard before this)

Answer 24

• pros: wider dynamic ranges, higher-quality sound, clearer audio output
• cons: larger file sizes, longer audio file transmission times, more processing power used up

(NB: the parts related to file sizes and transmission times may be resolved using compression - more on that later)

Question 25

(bonus) define the following:

frame rate

(hint: this has to do with videos but isn’t in the CIE syllabus at all)

Answer 25

the amount of video frames recorded within a single second

Question 26

compare the following methods of compression against each other:

lossless and lossy

(hint: the latter compresses further than the former)

Answer 26

• lossless: reversibly deconstructs extra data by indexing it for later; best suited for less-destructible applications (eg. XLS/EXE)
• lossy: irreversibly deconstructs extra data in an unnoticeable manner; best suited for more-destructible applications (eg. JPEG/MP3)

Question 27

consider how the following affects sound quality:

lossy audio file formats like MP3

(hint: the loss’s less noticeable than when reducing the sampling res)

Answer 27

1. perceptually-shaped softer sound/extrahuman range elimination (not really noticeable)
2. closer audio quality to that of a normal CD at higher bit rates

Question 28

consider how the following affects video quality:

lossy video file formats like MP4

(hint: again the loss’s less noticeable)

Answer 28

smaller video files that’re faster to transmit yet still closer to their original qualities

(this is especially important for video streaming - more on that in C2)

Question 29

consider how the following affects image quality:

lossy image file formats like JPEG

(hint: ditto)

Answer 29

smaller image files that still look closer to the originals despite being compressed by a factor of 5-15 w/ irreversible data loss

Question 30

list the processes involved in the following compression method:

RLE (run-length encoding)

(hint: think of patterns)

Answer 30

1. reversible data deletion by indexing each repeated string into two encoded values (for text)/each repeated color into an RGB code (for images)
2. flagging patterns containing more than one unit/iteration

(all this makes RLE more effective on longer runs of repeated units)

Question 31

list some other methods for compressing the following:

movies and images

Answer 31

• cropping
• decreasing resolutions/bit depths
• reducing frame rates