How internet works?

1. Digital representation (3)2. Networks fundamentals (4)3. Internet and Web (5,6)

(Digital representation) Summary Lec.3

How data is represented?

Binary system coding system (Numbers?Text (ASCII/others)? other data types?)

Binary

Computers see data in binary form

00001111

0 means false/off i.e. no electrical pulse

1 means true/on i.e. electrical pulse

A digit is a bit; highest bit is the first digit (00001111); the lowest bit is the last digit (00001111)

00001111 8 bits = byte (0000 4 bits = half a byte = Nibble)

When we say 4 bits then we can talk about 24 possible combinations since we have 2 digits that possibly fill each of the 4 places

So n bits means 2n possible combinations

Every word/picture/… are processed and stored in bits

So processor speeds: 8 , 16, 32 (standard) , 64-bit processor means it can handle 64 bits to be processed at the same time (simultaneously) i.e. the word here is 64 bits (or the processor’s speed)

Note: a character is stored in a byte !

So how many it takes to store words/ paragraphs…etc?

Q: 5 KB = ……… bytes = ……….. bits

Q: (3000 object * (500 bytes + 0.5 MB) = 3000* (0.5 KB +0.5 MB) = 1500 KB + 1500 MB = 1.5 MB+ 1500 MB = 1501.5 MB)

Bit 0 or 1Byte 8 bits (23)Kilobyte (about 1000 byte) 1024 bytes (210)Megabyte (about 1000 KB)

1024 KB (220)

Gigabyte (about 1000 MB) 1024 MB (230)Terabyte (about 1000 GB) 1024 GB (240)Petabyte 1024 TBExabyte 1024 PBZettabyte 1024 EBYottabyte (YB) 1024 ZB

Coding System

Converting a letter or info to a digit? How to code?.

info code “encoding” Code info “decoding”

Each type of data has a coding system (Text: ASCII, EBCDIC, and Unicode; Numbers: BCD; Multimedia and programs have other coding systems) ----Check abbreviations

BCD Example slide 14: (2 bytes) Ex: Slide 15: (this forms a byte and half)

Adding (dividing or subtracting) two codes give the right solution:

Note 1+1 in binary is not 2 (but 10) ; 3 is (11)

ASCII: A character is a byte (i.e. 8 bits-new- before it was 7 bits) –Most common

Printing and non printing characters are coded according to this key:

Example: Hello world:

1001000 1100101 …etc

The 8-bit ASCII is the same as old but new characters are added (using a new digit)

EBCDIC 8-bit IBM by mainframes, and Unicode32-bit for Arabic/chineese

Multimedia data and its encoding: (Audio: MP3 files are a compressed format for the bits; Video: are frames of still shoots consume much memory and need higher level of coding) + Images

Images are formed of a grid (small squares) with small digit dots called: Pixels (Pixel is the smallest unit holding a color)

Pixel (In black and white images: Monochrome) 1 bit i.e. 0 or 1Pixel in images with >2 colors depends (4 , 8, 24…)

A good image includes many pixels with many colors and so many bits! –but takes much memory! (positive correlation between size and no. of pixels)

GIF (8-bit format), JPEG (24-bit)….etc are compression types

info code “encoding” Code info “decoding”

How to decode?

Need to know what type of data is stored because the same digits combination can be decoded as text, number or image for example:

Quiz:

1. i.e. 1000 (1000 bytes =KB) = MB2. True (every file format is)3. Computers don’t use any numbering system other

than the “Binary system” -For all operations