Magnets used to store data

?

Magnet with unknown state

Current

N

S

Current

S

N

‘0’

‘1’

Binary Representation of Data

one bit “ 1” or “0” only 2 choices

two bits 00, 01, 10, 11 4 choices

three bits 000, 001, 010, 011,100, 101, 110, 111

8 choices

n bits has 2n choices

For example, 5 bits has 25 = 32 choices...more than enough to represent all the letters of the alphabet

Character "SS"codea 00001b 00010c 00011d 00100e 00101f 00110g 00111h 01000i 01001j 01010k 01011l 01100m 01101n 01110o 01111p 10000q 10001r 10010s 10011t 10100u 10101v 10110w 10111x 11000y 11001z 11010

Binary representationof lower case letters

5-bit Science Saturday code:

ex: k = 01011

0 1 0 1 1

Magnetic Data StorageA computer hard drive stores your data magnetically

Disk

N S

direction of disk motion

“ Write”Head

0 0 1 0 1 0 0 1 1 0 _ _

“ Bits” ofinformation

NS

“ Read”Head

Signal

Scaling Down to the Nanoscale

Increases the amount of data stored on a fixed amount of “real estate” !

Now ~ 50 billion bits/in2, future target more than 1 trillion bits/in2

25 DVDs on a disk the size of a quarter, orall Library of Congress books on a 1 sq ft tile!

NEW! Multi State Representation of Data

Disk

“ Write”Head

“ Read”Head

= =0 1

direction of disk motion

1 0 3 2

0

12

3

"CLUSTERS"

Character "SS"codea 001b 002c 003d 010e 011f 012g 013h 020i 021j 022k 023l 030m 031n 032o 033p 100q 101r 102s 103t 110u 111v 112w 113x 120y 121z 122

Multi state representationof lower case letters

……………