1. What is a computer? A computer is a device that:
Accepts input
Processes data
Stores data
Produces output
Let’s examine components in more detail…

2. What is a computer? A computer is a device that:
Accepts input: Input devices
Name as many as you can:

3. What is a computer? A computer is a device that:
Accepts input: Input devices
Name as many as you can:
Keyboard, mouse, scanner, bar code reader, light pen, infrared sensor, video camera and many more…

4. What is a computer? A computer is a device that:
Processes data: Processors
Name as many as you can:

5. What is a computer? A computer is a device that:
Processes data: Processors
Name as many as you can:
CPU, graphics processor, video controller, modem, and many more…

6. What is a computer? A computer is a device that:
Stores data: Storage devices
Name as many as you can:

7. What is a computer? A computer is a device that:
Stores data: Storage devices
Name as many as you can:
Main memory, hard drive, CD-ROM, DVD-ROM, memory card, tape drive, ZIP disk, floppy disk,

8. What is a computer? A computer is a device that:
Produces output: Output devices
Name as many as you can:

9. What is a computer? A computer is a device that:
Produces output: Output devices
Name as many as you can:
Monitor, printer, speaker, indicator light, and many more…

10. Data Representation A computer is a device that: Accepts input
Processes data
Stores data
Produces output
Input data transformed into output.
Data can be stored for repeated output.

11. Data Representation Spreadsheet data  graphs 3D models  animation
Vocals and MIDI  Song
Bar code  Price of item
Card and Pin #  Money from ATM

12. Data Representation
How can we represent information in a way that can be stored and manipulated by a computer?

13. Data Representation and Storage
External representation: computers use decimal digits (base ten), 26-character alphabet for easier human interaction via keyboard, terminal, printer
Internal representation: computers use binary system for numbers, letters, graphics, etc.

14. Data Representation
Internally, computers represent information as patterns of bits
A bit (binary digit) is either 0 or 1; these are symbols and have no numeric meaning
Storing a bit requires that a device can be in one (and only one) of just two states; analogous to true and false

15. Bit Storage
Why only two states? Why not use ten states to correspond with the base ten numbering system?

16. Data Representation Binary Numbers!!!
Sound  pitch  number  binary number
Letter  number  binary number
Image  color at each pixel  number  binary number

18. Decimal Number Systems
Base 10
Digits - 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
e.g =
= 3 x x x100
= 3 x x x 1 =

19. Binary Number System Base 2 Digits 0, 1 e.g. 1102 =
= 1 x x x 20
= 1 x x x 1 =
= 6

20. Counting in Binary Decimal Binary 0 0 1 1 2 10 3 11 4 100 5 101
Decimal Binary

22. Place and value
In a decimal number, each place value is 10 times greater than the place to its right.
In a binary number, each place value is 2 times greater than the place to its right.
For convenience, we group every four binary bits into a hexdecimal digit (1-9, A,B,C,D,E,F)
In a hexdecimal number, each place value is 16 times greater than the place to its right.

23. Binary Numerals 01101101 Bits are numbered from the right
b7 b6b5b4b3b2b1b0
Subscripts represent the place value
bi has place value 2i
Convert to decimal
b7 * 27+b6*26 + b5*25 +b4*24 +b3*23 +b2*22 +b1*21 + b0*20

24. Data Representation
100 = 1 * * = 1 *

25. Data Representation
Binary to Decimal = 1 * * * * * 20

26. Data Representation
Binary to Decimal = 1 * * * * * 20 = = 19

27. Excercise
1011b = ?d

28. Addition =? =

29. 4 bits and Hex ;0 ;1 ;2 ;3 ;4 ;5 ;6 ;7 ;8 ;9
;10 (Ah)
;11 (Bh)
;12 (Ch)
;13 (Dh)
;14 (Eh)
;15 (Fh)

30. Converting Binary to Decimal
Another method: repeatedly multiply by 2 and add next bit
e.g
0 x 2 = = 1
1 x 2 = = 3
3 x 2 = = 6
6 x 2 = = 13
13 x 2 = = 26
26 x 2 = = 53

31. Converting Decimal to Binary
Repeatedly divide by 2, recording remainders in reverse order
e.g. 53 / 2 = 26 R 1
26 / 2 = 13 R 0
13 / 2 = 6 R 1
6 / 2 = 3 R 0
3 / 2 = 1 R 1
1 / 2 = 0 R 1
giving

32. Data Representation use a fixed number of digits.
But how many bits do we need?
1 binary digit  0 or 1  2 possible chars
2 binary digits  00, 01, 10, 11  4 chars
3 binary digits  000, 001, 010, 011, 100, 101, 110, 111  8 chars

33. Data Representation Solution: use a fixed number of digits.
But how many bits do we need?
1 binary digit  0 or 1  2 possible chars
2 binary digits  00, 01, 10, 11  4 chars
3 binary digits  000, 001, 010, 011, 100, 101, 110, 111  8 chars
Notice a pattern? 12, 24, 38, …
the total number of character that can be represented by n bits is 2n

34. Number of bits
How many states can be represented with 1 bits, 2 bits, 3 bits, 8 bits ….
To represent N states, how many bits are needed.

35. Data Representation log2n
But how many bits are needed to store n symbols?
Or, how many bits are needed to represent n numbers?
log2n

36. Character Representation
1 byte = 8 bits = 1 character?
256 possible codes with 8 bits
Assign a character to each code
Common assignment
ASCII - American Standard Code for Information Interchange – defines first 128

37. ASCII Code Code Value Letter 0 Null character
Special Control Characters
10 \n = New line
32 Space
33-47, 58-64, Punctuation
A - Z
a - z

38. Interesting ASCII Choice?
Digits 0 through 9 seem strange?
Digit Dec Hex
… … …

39. Data Representation
American Standard Code for Information Interchange (ASCII ) defines 256 symbols that can be stored in a byte. Each symbol corresponds to a number from
Symbol
Decimal
Binary @ 64 A 65 B 66 C 67 D 68 E 69 F 70 G 71 H 72

40. Unicode International language coding standard Superset of ASCII
Various codes defined to use upper 128 bits for symbols and other languages

41. Memory Sizes Byte = 8 bits Kilobyte (K) = 210 = 1,024 bytes
Megabyte (Mb) = 220 = 1,048,576 bytes
Gigabyte (Gb) = 230 = 1,073,741,824 bytes

42. 16-bit Memory Word To store number 6, use 0000000000000110
Value 0 is
Largest value is = 65,535 = 216 − 1
32-bit word gives largest value > 4 billion