UNIT 1 - Computer Science

What is the difference between a kibibyte and a kilobyte

A kilobyte is 1000bytes and a kibibyte is 1024 bytes

State what is meant by Binary

A base 2 number system based on the values of 0 and 1 only

State what is meant by a bit

A binary digit

State what is meant by one’s compliment

every binary digit in a number is reversed to allow both negative and positive numbers to be representedS

State what is meant by hexadecimal

A number system based on the value 16 (Uses denary digits 0-9 then the letters A-F)

State what is meant by a memory dump

Contents of a computer memory output to a screen or printer

State what is meant by BCD

(Binary-coded decimal) is a number system that uses 4 bits to represent each denary digit

State what is meant by ASCII code

A coding system for all the characters on a keyboard and control codes

State what is meant by a character set

A list of characters where each character represents a unique binary value

State what is meant by UNICODE

A coding system which represents all the languages of the world (First 128 characters are the same as ASCII)

What is a binary digit known as

A bit

What base number system is binary

Base 2 number systemW

What base is hexadecimal

It is made up of 16 digitsW

What base is denary

Base 10 number system

What does a “1” in the first position of an 8-bit binary number respresent with two’s compliment

-128

In steps how do you do binary subtraction

Convert the negative number to it’s two’s compliment equivalent then add and ignore the ninth bit

What is the smallest unit of memory in a computer

A byte (8bits)

NOTE

IEC system uses x1024 (Kibi) and normally we use SI Base units system of x1000 (Kilo)

In IEC to move to next unit we multiply by x1024
In SI Base unites to move to the next unit we multiply by x1000

What memory storage system should RAM be measured in

IEC

For me how do you convert from hexadecimal to binary and to denary?

Never convert directly either convert from hexadecimal to binary then denary never direct contact between denary and hexadecimal it becomes too complicated

State one use of hexadecimal

Memory dumps are written in hexadecimal so errors can more easily be located

It is easier to find an error in hexadeciaml than in a sea of 0’s and 1’s

How does BCD work?

each nibble (4 bits) represents a digit

So a single byte can be used to represent two digits

State one common use of BCD

To display digits on a clock or calculator

When is hexadecimal often preffered?

When representing large values hexadecimal is often preffered as it takes fewer digits to represent a certain value than in binary

Why is it beneficial to use hexadeciamal over binary

The more bits there are in a number the harder it is for a human to read
Numbers with more bits are more prone to errors when being copied

Give me 3 other uses of hexadecimal

MAC Adresses

Color Codes

URLs

How many hexadeciaml digits does a MAC address typically consist of?

12

How many hexadecimal digits is typically a color code?

6 hexadecimal digits

How many binary digits are there in 1 hexadecimal digit

4

So 8 hexadecimal digits is 32 binary digits

State what is meant by bit overflow

When the sum of two binary numbers exceeds the given number of bits

In order state the binary prefixes and what they represent

Kilo - x10 to the power of 3

Mega - x10 to the power of 6

Gega - x10 to the power of 9

Tera - x10 to the power of 12

Peta - x10 to the power of 16

How many bits does standard ASCII character set use and how many characters can it represent

7 bits - 128 unique characters

Give one limitation of standard ASCII

It can only represent the English language and no special characters

State how many bits Extended ASCII uses and how many characters it can represent

8 Bits - 256 characters includes non-English characters

State what is UNICODE

A character set used to represent all the major languages and uses 16 bits per character / can represent 65,536 unique characters

Why was UNICODE created

To act as a universal standard

State one major drawback of UNICODE

It uses 16 bits to store each character so it takes up a lot more storage space than ASCII

State what is meant by a Bit-map image

A system that uses pixels to make up an image

State what is meant by a pixel

The smallest picture element that make up an image

State what is meant by color depth

The number of bits used to represent the colors in a pixel

e.g if each pixel uses 10 bits than it can represent 2 to the power of 10 / 1024 different colors

State what is meant by Bit Depth

The number of bits used to represent the smallest unit of a file

State what is meant by image resolution

The amount of pixels that make up an image

State what is meant by screen resolution

The number of horizontal and vertical pixels that make up a screen display

Can you display an image with an image resolution of 1000×1000 pixels on a screen with a screen resolution of 500×500 pixels

No either the image will simply not be displayed as it cannot be shown on the screen or the image become of lower quality

What is the difference between image resolution and screen resolutions

Image resolution - number of pixels that make up an image

Screen resolution - number of horizontal and vertical pixels that make up a screen display

State what is simply meant by resolution

The number of pixels per column and per row on a TV screen

State what is meant by pixel density

The number of pixels per square centimeter

State what is meant by vector graphics

Images that use 2D points to describe lines and curves and their properties that are grouped to form geometric shapes

How are images stored as bit-map images

As pixels stored in a 2D matrix of pixelsIs

Is there one define and set shape for pixels?

No they can take multiple shapes, like squares circles and rectangles

What 2 things happen when the bit depth of a pixel increase

The number of possible colors the pixel can represent increases

The file size of the image increases

What happens to the quality of an image as it’s resolution increases

The quality and file size of the image increase with it

In an image what is each pixel stored as

Binary code

What is created when a bitmap image is saved

A file header

What does a file header contain

General information regarding the image such as:

• File type

• File size

• Image resolution

• Color depth

  • Any type of compression if used

Is there any way to maintain the quality of an image while reducing it’s file size

Comrpession

How is a vector graphic created

Using mathematical equations and points

What are typical examples of when vector graphics are used

Clipart or logos

State one advantage of vector images

They are infinitely scalable, meaning you increase the size of the image as much as you want without loss of quality

What does every vector graphic contain

A drawing list

Where is the drawing list of a vector graphic found

In the file header

What are the 3 things which a typical drawing list will contain

• Commands used to create each object in the image

• Attributes that define the properties of each object

  • Relative position of each opbject
    
    CAR
    COMMANDS used to create
    ATTRIBUTES that define properties
    RELATIVE POSITION

In a drawing list are the dimensions of an object defined?

They are not meaning that scaling up does not result in a loss of quality

Compare between bit-map images and vector images

What 3 things need to be considered when choosing between bitmap and vector images

Does the image need to be resized?

Does the image need to be drawn to scale?

Does the image need to look real?

State one more time what are VECTOR GRAPHIC IMAGES

Images that use 2D points to describe lines and curves and their properties so that when they are grouped the form geometric shapes

What device is used to record sound

A microphone

To be able to playback and record a sound what needs to be done

It needs to be sampled and stored

Sound waves naturally are what type?

Analogue

How is sound recorded and converted into a digital signal

Multiple times each second the amplitude of a sound wave is recorded and stored as a binary value at a point in time, this is called sampling

The higher the amplitude the higher the…….?

Sound

State what is meant by the sampling rate

The amount of samples taken per second. This is represented in hertz

State what is meant by the sampling resolution

The number of bits used to represent each sound sample

Why does increasing the bit depth / sample resolution increase the accuracy of the sound file

As more bits means that the amplitude can be more accurately sampled

What is the effect of increasing the sample rate or sample resolution of a sound file

Better sound quality in both and in both a larger file size

HOWEVER
INCREASING Sample rate —- more detail

INCREASING Sampling resolution ——- Bigger range

State the difference between a kibibyte and a kilobyte

• Kibibyte is 1024 bytes and kilobyte is 1000 bytes

• Kibibyte is binary prefix and kilobyte is denary prefix

State the difference between a kibibyte and a megabyte

• kibibyte = 1,024 bytes // 2¹⁰ bytes and megabyte = 1000 kilobytes // 1 000 000 bytes // 10³ kilobytes //

• kibi is binary prefix and mega is denary prefix

State the difference between a kibibyte and a kilobyte

• Kibibyte is 1024 bytes and kilobyte is 1000 bytes • Kibibyte is binary prefix and kilobyte is denary prefix

State the difference between a kibibyte and a megabyte

• kibibyte = 1,024 bytes // 2¹⁰ bytes and megabyte = 1000 kilobytes // 1 000 000 bytes // 10³ kilobytes // 10⁶ bytes • kibi is binary prefix and mega is denary prefix

State the difference between a tebibyte and a gigabyte

• A tebibyte = 1024 gibibytes / 1 048 576 kibibytes / 2⁴⁰ bytes whereas a gigabyte = 1000 megabytes / 1 000 000 kilobytes / 10⁹ bytes • Tebi is binary prefix, giga is denary prefix

Identify two differences between binary prefixes and decimal prefixes

• Binary is in powers of 2 whilst decimal is in powers of 10 • Any example of values, e.g. kibibyte is 1024 bytes whilst kilobyte is 1000 bytes

Completed statement (fill-in-the-blank version)

A kibibyte has a BINARY prefix. Three kibibytes is the same as 3072 bytes. A megabyte has a DECIMAL/DENARY prefix. Two terabytes is the same as 2000 gigabytes.

Accepted working for hexadecimal → denary

A04: (10 × 16²) + 4 // (10 × 256) + 4 // 1010 0000 0100 → Answer 2564 C0F: 1100 0000 1111 // 2048 + 1024 + 8 + 4 + 2 + 1 // (12 × 16²) + 15 // 3072 + 15 → Answer 3087 1FAB → 8107

Verified conversion answers from the papers

denary 241 → F1 = 110001100111 → C67 101100111010 → B3A = 1110001100111011 → E33B denary 558 → 0010 0010 1110 and 22E number of unique values in 16 bits = 2¹⁶ // 65536

Minimum number of bits needed to store each item

the hexadecimal value F139 — 16 bits 16 000 000 unique amplitude values — 24 bits an IPv4 address — 32 bits 256 unique colours — 8 bits an IPv6 address — 128 bits the denary value 65 000 — 16 bits

Explain how to convert a two's complement integer into denary

• Flip each bit then add 1 … … then convert the new binary number into denary • OR: the most significant 1 bit is treated as the corresponding negative denary value … … add the other positive corresponding denary values

Ranges you are expected to know

Smallest 8-bit two's complement: 1000 0000 Largest: 0111 1111 Largest unsigned integer in 8 bits: 255 Smallest 12-bit two's complement: 1000 0000 0000 Smallest 16-bit two's complement: 1000000000000000

One's complement

Give the 8-bit one's complement of −120: Working +120 = 0111 1000 → Answer 1000 0111

Worked two's complement → denary answers

11100010 → −30 = 100110010111 → −1641 111110111100 → −68 (working: flip bits + add 1, OR −2048+1024+512+256+128+32+16+8+4) 01101011 → 107 = 011010110001 → 1713

How a binary addition is marked

• Working — carried values clearly indicated • Correct answer • Overflow clearly indicated as overflow

How a binary subtraction is marked — two accepted methods

• Two's complement method — change the number being subtracted to its two's complement and add. … Needs to show the conversion AND the addition. • Direct subtraction method — subtract the second number from the first. … Needs to show the carries/borrows for the working mark.

State what is meant by an overflow

• The answer is too long to be represented in the same number of bits as the binary numbers being added • The answer cannot be represented in the number of bits available • The answer is larger than the maximum positive number that can be stored in the register • The answer is smaller than the most negative number that can be stored in the register

Describe the difference between a right logical and a right arithmetic shift

• A logical shift moves all bits to the right and inserts zeros in the appropriate leftmost bits • An arithmetic shift moves all bits to the right but copies the sign bit into the Most Significant Bit (MSB)

Verified shift answers from the papers

3-place right logical shift on 11001100 → 00011001 2-place left logical shift on 01001111 → 0011 1100 logical left shift of 2 on 11001010 → 0010 1000 arithmetic right shift of 3 on 10011110 → 1111 0011 arithmetic right shift of 3 on 10010011 → 1111 0010 logical right shift of 2 on 01100010 → denary 24 cyclic left shift of 4 on 10010101 → 0101 1001

Identify one application of BCD and justify why BCD is used

• An application that performs financial / banking calculations … because financial transactions use only two decimal places and must be accurate, no accumulating / rounding errors, and it is difficult to represent decimal values exactly in normal binary • Electronic displays, e.g. calculators, digital clocks … because visual displays only need to show individual digits … because conversion between denary and BCD is straightforward • The storage of the date and time in the BIOS of a PC … because conversion between denary and BCD is more straightforward • Barcode systems … because conversion between denary and BCD can be accurately completed

Verified BCD conversions

denary 964 → 1001 0110 0100 = denary 108 → 0001 0000 1000 BCD 100001100101 → 865 = BCD 010101110011 → 573 ASCII 'h' (denary 104) → BCD 0001 0000 0100 denary 160 → BCD 0001 0110 0000 = denary 2486 → binary 1001 1011 0110