1. Storage in Computers I/O
Magnetic disks:
A magnetic disk consists of one or more aluminum platters with a magnetizable coating.
1. Originally, as much as 50 cm in diameter.
Now, 3 – 12 cm. In notebook pc’s or
cameras, they can be as small as1-2cm in
diameter.

2. Magnetic Disks ---Cont…
2. Capacity 5-20MB only a dozen years
ago. Now, they can be as large as 100GB.
*** Compare: An ordinary computer science textbook contains about 1 million bytes. 100GB can store 100,000 such books, basically, a whole library can be put into one disk.
3. Fast and reliable ,000turns/s
7,200turns/s is typical.

3. Physical HD . Track 5-10microns Sector A Head Head movement
A piece of enlarged track

4. Physical HD---cont….
Collective movement .

5. Floppy and Tape Drives
They are shrink their roles in PC and soon will be totally disappear.
Currently, 3 ½ “ floppy still a convenient tool for personal use, especially for students.
Tape drive can hold more information. However, the speed has been a major issue.

6. CD – ROM, DVD-ROM, DVD-RAM
Because of the capacity, reliability and durability, they have become more and more popular.
Which includes CD-R and CD-RW

7. The NEW technologies are coming
There are a lot of research going on in information storage technologies.
1. Optical 3-D storage
2. Use spin-up and spin-down of atoms.
3. Magnetic RAM (IBM)

8. Homework
1. How many books a 4.7GB DVD-ROM can store? (Assuming that each book has an average of 1 million characters)
2. Compare between HD and CD-RW, can we replace HD with CD-RW?
3. If you have the choice of the future storage devices and storage media, what kind of properties you like them to have?