Magnetic Data Storage
A computer hard drive stores your data magnetically
“Read” “Write”
Head Head
Signal
S N
Disk
N S
0 0 1 0 1 0 0 1 1 0 _ _
“Bits” of
direction of disk motion information
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, or
all Library of Congress books on a 1 sq ft tile!
Binary Representation of Data
one bit “1” or “0” only 2 choices
two bits 00, 01, 10, 11 4 choices
000, 001, 010, 011,
three bits 8 choices
100, 101, 110, 111
n bits has 2n choices
For example, 5 bits has 52 = 32 choices...
more than enough to represent all the letters of the alphabet
Character ASCII code "SS" code
Binary representation a 1100001 00001
of lower case letters
b 1100010 00010
c 1100011 00011
d 1100100 00100
e 1100101 00101
f 1100110 00110
g 1100111 00111
h 1101000 01000
i 1101001 01001
5-bit Science Saturday code:
j 1101010 01010
k 1101011 01011
l 1101100 01100
ex: k = 01011 m
n
1101101
1101110
01101
01110
o 1101111 01111
p 1110000 10000
q 1110001 10001
r 1110010 10010
s 1110011 10011
t 1110100 10100
u 1110101 10101
v 1110110 10110
w 1110111 10111
x 1111000 11000
y 1111001 11001
z 1111010 11010
ASCII = American Standard Code for Information Exchange
"SS" = Science Saturday