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
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.
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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?
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13. Next stage:
Video: How the Altair 8800 started the PC revolution (Part 2)
Outcomes:..
Operating system
Software usage
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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!
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15. Mac
Windows
Linux
Red Hat
UNIX
Sugar OS (XO computer for kids)
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17. Computers platform
= OS + microsprocessor (CPU)
Introducing the Mac
Classic Mac OS (1984–2001)
1984 –
Mac OS first commercial GUI
Mac OS X (since 2000)
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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
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23. Intermediated experience
◦ Command line vs GUI cp Disney’s approach
◦ OS, software are intermediaries
OS is a stack of metaphors and abstractions ..to covert
the information you’re 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 Disney’s approach
◦ Technological perspective:
Direct control (user) vs system control (GUI) cp Disney’s
immersive process
◦ User’s 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
