Java Reference
In-Depth Information
Medium
1996
1997
2000
2004
2006
2008
2011
RAM
$45.00
7.00
1.500
0.3500
0.1500
0.0339
0.0138
Disk
0.25
0.10
0.010
0.0010
0.0005
0.0001
0.0001
USB drive
-
-
-
0.1000
0.0900
0.0029
0.0018
Floppy
0.50
0.36
0.250
0.2500
-
-
-
Tape
0.03
0.01
0.001
0.0003
-
-
-
Solid State
-
-
-
-
-
-
0.0021
Figure8.1
Price comparison table for some writable electronic data storage
media in common use. Prices are in US Dollars/MB.
Access Memory (RAM), while secondary storage refers to devices such as hard
disk drives, solid state drives, removable “USB” drives, CDs, and DVDs. Primary
memory also includes registers, cache, and video memories, but we will ignore
them for this discussion because their existence does not affect the principal differ-
ences between primary and secondary memory.
Along with a faster CPU, every new model of computer seems to come with
more main memory. As memory size continues to increase, is it possible that rel-
atively slow disk storage will be unnecessary? Probably not, because the desire to
store and process larger files grows at least as fast as main memory size. Prices
for both main memory and peripheral storage devices have dropped dramatically
in recent years, as demonstrated by Figure 8.1. However, the cost per unit of disk
drive storage is about two orders of magnitude less than RAM and has been for
many years.
There is now a wide range of removable media available for transferring data
or storing data offline in relative safety. These include floppy disks (now largely
obsolete), writable CDs and DVDs, “flash” drives, and magnetic tape. Optical stor-
age such as CDs and DVDs costs roughly half the price of hard disk drive space
per megabyte, and have become practical for use as backup storage within the past
few years. Tape used to be much cheaper than other media, and was the preferred
means of backup, but are not so popular now as other media have decreased in
price. “Flash” drives cost the most per megabyte, but due to their storage capac-
ity and flexibility, quickly replaced floppy disks as the primary storage device for
transferring data between computer when direct network transfer is not available.
Secondary storage devices have at least two other advantages over RAM mem-
ory. Perhaps most importantly, disk, “flash,” and optical media are persistent,
meaning that they are not erased from the media when the power is turned off. In
contrast, RAM used for main memory is usually volatile — all information is lost
with the power. A second advantage is that CDs and “USB” drives can easily be
transferred between computers. This provides a convenient way to take information
from one computer to another.
