Topic 2

Question 1

2.1.2 Two’s complement

Answer 1

• -> The MSB is a minus number as well as a sign bit.
• -> always remember to write the + sign

negative numbers:

1) convert to the unsigned equivalent 8 bit binary
2) flip the bit
3) add 1 arithmetically

Question 2

2.1.3 denary to binary

Question 3

2.1.5 overflow error

Answer 3

Overflow error means that the result of the calculation is too large for the space allocated.

The way a computer handles this will depend on how its set up:
It could crash and report an overflow error.
It could truncate the answer.
It could wrap the number around back to 0.

Question 4

2.1.6 hexadecimal to binary

convert C3 to binary

Answer 4

1100 0011

1) convert each digit to denary
2) convert denary to binary
3) combine to get binary number

Question 5

2.1.6 binary to hexadecimal

convert 1011 0011 to hexadecimal

Answer 5

B3

1) split the byte into two nibbles
2) convert each to denary
3) add these together to get hexadecimal

Question 6

2.2.1 ASCII

Answer 6

ASCII (American Standard Code for Information Interchange)

ASCII enables computing devices to communicate with another and to translate their communication into identical information.

Limitations:

• ascii is only 7 bits, so can only store up to 128 unique characters.
• other languages have characters that can be represented with only 7 bits.
• more bits are needed to represent some alphabets.

Question 7

2. 2.2 - define:
   a) pixel
   b) resolution
   c) colour depth

Answer 7

a) pixel
- a picture element, a tiny square of colour

b) resolution
- describes how tightly packed the pixels are
- describes the number of pixels per inch.
- if you enlarge an image it becomes more pixelated and has a lower resolution.

c) colour depth
- the number of bits used to encode the colour of each pixel in a bitmap image.
the more bits used to encode the colour, the greater the number of actual colours that can be represented in the image so that is is more detailed.

2ⁿ

Question 8

2.3.1 units

Answer 8

Kiss My Gross Toes

Kibibyte
Mebibyte
gibibyte
tebibyte

Question 9

2.3.2 lossy compression

Answer 9

+ bigger reduction in file size
+ data removal is not noticeable human eye or ears

• removes actual data
• original cant be reconstructed

uses: image size and digital sound recording
examples: MP3 audio files and JPG image files

Question 10

2.3.2 lossless compression

Answer 10

+ encodes data, rather than removes it
+ original can be reconstructed exactly

• not as much reduction as lossy compression

uses: text files and graphic files with a low colour depth
examples: compressed text files, GIF and PNG image files and FLAC and ALAC audio files.

Question 11

2. 3.2 compression
   a) reasons for compressing files
   b) advantages of file compression

Answer 11

a)

1) reduce storage requirements
2) reduce network transmission time

b)

• less internet bandwidth is used when files are downloaded
• transfer time is faster
• less storage space is needed
• smaller files reduce congestion on the internet
• audio and video files can be streamed