Specifications

10
• low power requirements to prolonging battery life
• low cost (Figure 2)
Flash memory offers all but the last; but as people become more accustomed to the technology
and increasing demand allows production to increase also, costs will continue to decline as they
have for the last few years (Figure 2).
$0.00
$0.02
$0.04
$0.06
$0.08
$0.10
$0.12
$0.14
$0.16
$0.18
$0.20
2HD
floppy
disc
flash card
64 MB
flash card
128 MB
flash card
256 MB
flash card
512 MB
flash card
1GB
flash card
2GB
flash card
4GB
CD-RW
700 MB
Costs Per Megabyte
cost per megabyte
Expressing file sizes
Computers calculate in binary form; humans calculate in decimal form because of our 10 fingers. Even
though “digital” comes from the Latin word for finger, digital data are calculated as binary amounts. The
difference has led to a great deal of confusion over capacities. The numerical expressions for the large
amounts of data use prefixes from Latin and Greek decimal numbers. When applied to binary numbers,
these terms are not accurate because the binary numbers are always slightly greater than the decimal
expressions. As the numbers grow in value, the difference becomes larger. Computers express file sizes in
binary terms. Storage media such as drives, optical discs, and flash media generally use the decimal
method according to the standard recommended by IBM in the 1950s. The difference in value was of little
significance then, but as capacities have grown, the difference has also grown:
Common
Original
Literal, decimal
Suggested Change
Term
Prefix
Source
Meaning
meaning
Value in Binary Terms
Difference
For Binary Values
kilobyte
kilo
Greek
"thousand"
1,000 1,024
2%
kibibyte
megabyte
mega
Greek
"big"
1,000,000
1,048,576
5%
mebibyte
gigabyte
giga
Greek
"giant"
1,000,000,000 1,073,741,824
7%
gibibye
terabyte
tera
Greek
"monster"
1,000,000,000,000
1,099,511,627,776
10%
tebibyte
petabyte
peta
Greek
“five”
1,000,000,000,000,000 1,125,899,906,842,620
13%
pebibyte
exabyte
exa
Greek
“six”
1,000,000,000,000,000,000
1,152,921,504,606,850,000
15%
exbibyte
The difference is most obvious when one compares the stated capacity of some storage media with the
computer’s calculation of that capacity. A “10GB drive,” for example, may have 10 billion bytes of storage
capacity, but the computer will divide by 1,024 to determine the number of gigabytes rather than by 1,000; so
it will claim capacity to be 9.3 GB, not 10GB. A 4.7GB DVD holds almost 4.7 million bytes of data, but in
Figure 2