1. Dr Kathy Egea COMP1900 week 3 1

2. More on computers (cont from week 2) Digitization of data and its storage Interface as mediator COMP1900 week 3 2

3. History of computers Computer functions Bits and bytes Software application programs and system programs Storage of data hardware Input of data hardware COMP1900 week 3 3

4. bits Bits are tiny electrical components that can hold a very small positive charge (represented as 1) or negative charge (represented as 0) speed of processing data is described in bits bytes One byte is divided into 8 bits (binary digit) A byte can store a letter of alphabet or a small number, see next page storage of data (ie in computer memory) is divided into these tiny storage locations described in bytes COMP1900 week 3 4

5. Bit 0 or 1 byte = 8 bits Eg 10011101 This represents the number 157, How? Using binary notation Each position is a power of 2, with the lowest power on the left Compare with the decimal system 245 235 = 200 + 30 + 5 = 2 * 102 + 3 * 101 + 5 * 100 ( note that 100 = 1) COMP1900 week 3 5

6. 1 0 0 1 1 1 0 1 20 (=1) 21 (= 2) 22 (= 4) 23 (= 8) 24 (=16) 25 (=32) 26 (=64) 27 (=128) 10011101 = 1 * 27 + 0*26+ 0 * 25 + 1 *24 + 1 * 23 + 1 * 22+ 0 * 21 + 1 * 20 = 1 * 128 + 0*64 + 0 * 32 + 1 *16 + 1 * 8 + 1 * 4 + 0 * 2 + 1 * 1 = 128 + 0 + 0 + 16 + 8 + 4+ 0 + 1 = 157 COMP1900 week 3 6

7. Any digital data Numbers Characters images (Pixels) see image Music digitized sound wave (samples) Quality CD song is divided into 44,000 samples per second COMP1900 week 3 7

8. Hard drive disk (Magnetic storage) data stored in concentric circles called tracks; - pie shaded wedges sectors; - cluster is a group of sectors on one track - drive stores an index of all the sector (and track) numbers in a table Disk structure: (A) track (B) geometrical sector (C) track sector (D) cluster COMP1900 week 3 8

9. A cross section of the magnetic surface in action. COMP1900 week 3 9

10. Saving a file Computer looks at the table to see what clusters are free, record the file information on the available clusters ( ie writes the bits that make up the file on one or more clusters of the drive) Opening a file computer searches the table to locate marker for clusters, locates the file data and reads the file Deleting a file delete only the reference in the table COMP1900 week 3 10

11. First computers were mainframes (eg IBM 360) Computers work using programs (set of instructions) CPU or processor executes these programs Program entry via Teletype (line by line interaction with computer) Batch mode processing (series of cards with holes) Process could take all night to get output from the computer Ie big calculator. COMP1900 week 3 11

12. Invention of microprocessor 1972 Intel 8080 (1973) 8 bit processor First PC - Altair 8800 cost $395 Video How the Altair 8800 started the PC revolution (Part 1) So what does the Altair do? How? COMP1900 week 3 12

13. Next stage: Video: How the Altair 8800 started the PC revolution (Part 2) Outcomes:.. Operating system Software usage COMP1900 week 3 13

14. Jobs and Woznaik founders of Apple idea to selling formation processing machines for use in the home (1982) Video: advertising campaign for Macintosh (physical reality) Bill Gates and Paul Allen Idea to sell computer operating systems Video: foundation of Microsoft No physical reality it came in a disk! COMP1900 week 3 14

15. Mac Windows Linux Red Hat UNIX Sugar OS (XO computer for kids) COMP1900 week 3 15

16. COMP1900 week 3 16

17. Computers platform = OS + microsprocessor (CPU) Introducing the Mac Classic Mac OS (19842001) 1984 Mac OS first commercial GUI Mac OS X (since 2000) COMP1900 week 3 17

18. Windows PC (Bill Gates) 1985 Windows 1.0 The first version of Microsoft Windows included Windows Paint, a simple graphics paint program Windows Write, a simple word processor An appointment calendar A cardfiler MS notepad A clock A control panel Game called Reversi Clipboard COMP1900 week 3 18

19. MAC OS vs Windows OS not interchangeable Different processors, and software platform dependent Mac system better reliability, better documentary recovery, but more expensive that PCs Mac OS X Leopard built on UNIX OS with intel chip Now designed to share same files Today Mac and Windows very similar GUI Video: Microsoft's Vista Copies Apple OS? Jan 2007, New York Times Technology : http://www.youtube.com/watch?v=JKuYQwm1yNs&feature=related 19 COMP1900 week 3

20. Linux Linux is a free Unix-type operating system originally created by Linus Torvalds with the assistance of developers around the world. Developed under the GNU General Public License , the source code for Linux is freely available to everyone See http://www.linux.org/ COMP1900 week 3 20

21. One Laptop per child XO computer, uses Sugar OS focuses on activities rather than applications, first screen has icons representing home, friends, neighbourhood Computer has built in microphone, and webcam for mm creations Emphasis is on learning by exploring and expressing collaborate, wireless mesh network potential for every activity to be networked, browsing, extend community beyond borders Uses a journaling technique for file management records what the children have done looking like a scrap book of events http://www.olpcnews.com/ COMP1900 week 3 21

22. Neil Stephenson (1999) . In the beginning there was the command line. http://www.locusmag.com/2004/Issues/08Stephenson.html COMP1900 week 3 22

23. Intermediated experience Command line vs GUI cp Disneys approach OS, software are intermediaries OS is a stack of metaphors and abstractions ..to covert the information youre working on.. into the necklace of bytes that are the only things computers know how to work with. Stephenson (1999, p7). Structure GUI interface access to OS , hardware, software, networks, internet File system access to hard drive (HD) COMP1900 week 3 23

24. Operating system, and application software, are intermediaries "Disney does mediated experiences better than anyone. If they understood what OSes are, and why people use them, they could crush Microsoft in a year or two." from "In the beginning". COMP1900 week 3 24

25. Result of hardware + software (OS + applications) Command line vs GUI interaction cp Disneys approach Technological perspective: Direct control (user) vs system control (GUI) cp Disneys immersive process Users perspective user knowledge/preconceptions/expectation of operation; users want meaningful interaction Basic rule: User mental model to match system image (Normal 1988) COMP1900 week 3 25

26. Desktop/GUI gives access to file system, operating system, network, internet/www different layers of intermediary action network (OSI), hardware, operating system, and software file system gives access to hard-drives COMP1900 week 3 26

27. End COMP1900 week 3 27