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AS & A Level Computer Science 9608 REVISION NOTES
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AS & A Level Computer Science 9608 REVISION NOTES
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AS & A Level Computer Science 9608REVISION NOTES
1.1 Number Representation
What are binaries? - correct answer-o Values stored as a series of ones and zeroes
o A single 0 or 1 is called a binary digit or bit.
o Any group of 0s & 1s can represent a character
128 64 32 16 8 4 2 1
00000000
o E.g. 65 in binary is 1000001
1.1 Number Representation
What are BCD Representation? - correct answer-o Each digit in the number is written
separately in a
series of 4 bits
o E.g. 398 in BCD
o 3 = 0011 9 = 1001 8 = 1000
o 398 = 0011 1001 1000
o Use of BCD: used in business applications (arithmetic)
where every digit has to be retained in a result
1.1 Number Representation
What are Hexadecimal Number? - correct answer-o The base-16 number system (counting
in 16)
o After 9, numbers represented by letters from A to F
256 16 1
000
-(HEXADECIMAL TO DENARY)
o E.g. A5 in Denary = (16×10) + (1×5) = 165
-(DENARY TO HEXADECIMAL)
o E.g. 65 in Hexadecimal = 65 ÷ 16 = 4 𝑅𝑒𝑚𝑎𝑖𝑛𝑑𝑒𝑟 1
∴ = 41 H
-(HEXADECIMAL TO BINARY)
o Quick way of translating hexadecimal to binary is by converting the hexadecimal to BCD
o E.g.
A5 in Binary:
A = 1010, 5 = 0101
A5 = 10100101
1.1 Number Representation
What are 2's Complement? - correct answer-o We can represent a negative number in
binary by making the most significant bit (MSB) a sign bit, which will tell us whether the
number is positive or negative
,-128 64 32 16 8 4 2 1
MSB 0 0 0 0 0 0 LSB
1.1.2 Images
How data for a bit-mapped image is encoded? - correct answer-A bitmapped image is
encoded by assigning a solid color to each pixel.
1.1.2 Images
What are Pixels? - correct answer-Pixels are small blocks of addressable areas and the
color they have is represented by binary and stored as bits.
1.1.2 Images
What are File Header? - correct answer-They are a few bytes of binary and represents basic
information about the graphic, such as image resolution, size and number of colors.
1.1.2 Images
Define Image Resolution? - correct answer-It is the amount of pixels an image contains per
inch/cm
1.1.2 Images
Define Screen Resolution? - correct answer-It is the number of pixels per row by the number
of pixels per column.
1.1.2 Images
What is color depth? - correct answer-It is the number of bits used to represent the color of a
single pixel
An image with n bits has 2^n colors per pixel.
File Size = Number of Pixels x Color Depth
1.1.2 Images
What is a vector graphic? - correct answer-They are images defined using mathematics &
geometry i.e. points, lines, curves & shapes/polygon(s)
Objects and properties are stored mathematically
1.1.2 Images
What is a drawing list? - correct answer-It is a set of commands used to define a vector
1.1.2 Images
How typical features found in bit-mapped and vector graphics software are
used in practice? - correct answer-Vectors are scalable and do not pixelate like a bitmap
image therefore are used by corporations to create logos as they can be resized without
losing quality
Bit-mapped images are used by general computer users as they are not big in file size and
can be manipulated.
1.3 Sound
, How sound is represented and encoded? - correct answer--Sound are vibrations that travel
through a medium
-Sound waves are continuous in nature, which means there is infinite amount of detail for a
sound.
• Analogue to Digital Converter (ADC): converts analogue sound into digital signals which
can be digitally stored
• Digital to Analogue Converter (DAC): converts digital signals into analogue sound that can
be output
• An analogue sound wave is picked up by a microphone
and sent to an ADC in the form of analogue electrical
signals. Once the sound wave is converted into a digital
form it can be stored and manipulated
1.3 Sound
What is Sampling Rate? - correct answer-• Sound in analogue form can be represented by
wave forms; the height of these waves can be sampled regularly with the height being
represented by a bit-code
• Sampling Rate: number of samples taken per second
1.3 Sound
What is Sampling Resolution? - correct answer-It is the No. of bits assigned to each sample
• The sampling resolution allows you to set the range of volumes storable for each sample
• The quality of a sound produced using a sound sampler depends on the sampling rate and
sampling resolution
1.3 Sound
how file sizes depend on sampling rate and sampling resolution? - correct answer-• Higher
sampling rate/resolution means larger file size
1.3 Sound
What is bit Rate? - correct answer-It is the number of bits required to store 1 sec of sound
𝐵𝑖𝑡 𝑅𝑎𝑡𝑒 = 𝑆𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑅𝑎𝑡𝑒×𝑆𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
𝐹𝑖𝑙𝑒 𝑆𝑖𝑧𝑒 = 𝐵𝑖𝑡 𝑅𝑎𝑡𝑒×𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑆𝑜𝑢𝑛𝑑
1.4 Video
What is meant by Frame Rate? - correct answer-It is the Number of still Pictures per unit of
time of video.
-Higher frame rate, better quality video = greater size
1.4 Video
What is meant by Interlaced encoding? (e.g. 1080i): - correct answer-o Old Technology (70
years ago)
o Each field of a video image displays every other
horizontal line of a complete image ∴ doubles FPS
o Horizontal lines often visible to eye due to distortion
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