|Wikipedia's article on binary numbers
Wikipedia's article on the history of computers
Wikipedia's article on computer data storage
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|Bits and bytes
All modern computers are digital, which means that all of the
information going in or coming out of them, whether it's text, images,
program instructions or whatever, is converted to and dealt with as
numbers. Further, because of the way computers work, the numbers
are binary, rather than the customary decimal numbers. Probably
because humans have ten fingers, we seem to have always preferred the
decimal system, with ten symbols representing quantities from 0 to 9,
and with each place value worth ten times the preceding place value, as
in ones, tens, hundreds, thousands, etc. Because computers are
based on two-state switches that are either on or off, much like the
familiar light switch, the binary, or 'base 2' system works best.
When current is flowing through a switch, it represents the number 1,
and when current is not flowing, it represents the number 0.
Zeroes and ones are all there are, but in order to deal with larger
numbers and more than yes-or-no and other two-state situations, the
switches are arranged in groups of eight (called 'bytes') where each
switch signifies the place value of a single binary digit, or
'bit.' Binary place values are worth two times the preceding
place value, as in ones, twos, fours, eights, sixteens, thirty-twos,
sixty-fours and one hundred twenty-eights (to complete the byte.)
Each byte represents a number in the range of 0 to 255, or 00000000 to
11111111 as they would be written in binary numerals. With
numbers representing everything, there's a lot of converting and
translating going on. For example, the system used to represent
the letters of the alphabet and all of the characters found in a
typical keyboard is called the ASCII code. The letter A is the
number 65 (decimal) and written in binary notation as 01000001 (or
0-128s, 1-64, 0-32s, 0-16s, 0-8s, 0-4s, 0-2s, and 1 one.
Chips and bits and bytes
The first electromechanical digital computers were developed in the
late 1930s. The switches used in them were typically relays,
similar to the familiar solenoids used to remotely unlock outer doors
in apartment buildings. In a relay, a current is applied to an
electromagnet, which operates a switching mechanism mechanically.
Switch on = 1 and switch off = 0. By the early 1940s, the
clickety-click relays were replaced with significantly faster devices
called vacuum tubes, which are electronic valves that moderate the flow
of current through them. Current high = 1 and current low =
0. By the 1950s, vacuum tubes were replaced by solid state
electronic valves called transistors that used a type of metal that
only conducts current in one direction, called a semiconductor, instead
of a vacuum. These switches were smaller, faster, more reliable
and they used less current and generated less heat than vacuum
tubes. By the 1960s, scientists had figured out how to print
microscopic transistors on silicon or some other semiconductor, and
were able to group thousands and eventually millions of transistors
into a very small package called an integrated circuit chip.
These devices were about the size of a match head and featured switches
that were faster, smaller, more reliable and used even less current
than the original transistors. Now, each year brings advances in
miniaturization. The switches get smaller and closer
together. Current has less distance to travel and so arrives more
quickly, and the power of the computers based on them grows.
The math of storage
Modern computers use special integrated circuits, called memory
modules, to temporarily store programs and data, but they also
incorporate internal and external devices that allow for more permanent
retention. The first storage devices used cards with holes in
them to represent the binary digits. The holes were read by wires
passed over the cards that either made contact behind the card if there
happened to be a hole, or no contact if not. Hole = 1, and no
hole = 0. The cards were replaced by magnetic tape that stored
the digits as tiny magnets. The magnets were formed in a magnetic
kind of rust that was bonded to thin plastic called mylar. All
magnets are polarized, that is, they possess direction, and in this
system a magnet polarized in one direction = 1, and one polarized in
the other direction = 0. Tape is wound past the electromagnetic
tape head either forward or backward but can only be recorded or read
in one direction and as a single stream on the tape. Thus the
tape system has linear access to the data in that the tape must be
advanced or rewound to the specific spot where the required data sits,
or to a suitable spot to begin recording. Magnetic tape was
replaced with spinning disks of the same material in a system that uses
a read/record head mounted on an arm that can span the distance from
the inner edge of the disk to the outer. This system has random,
near-instant access to the data and is still in use today in hard
disks, though the removable kind, like floppy disks, are not used much
any more. A problem with the magnetic system is corruptibility of
the data due to magnetic influence, which can come from a variety of
sources, like magnets for example.
An optical system using compact discs replaced magnetic storage.
A laser is used to burn microscopic pits into the shiny surface of the
disc, and another laser is used to read the pits. A pit = 1, and
still shiny = 0. The advantages of this system include
efficiency, speed, and reliability, sort of. The jury is still
out on that last one, and no one really knows how long a CD-ROM or
DVD-ROM will last before errors develop. Pits happen!
The eight-bit byte is the unit of storage, but storage capacity values,
whether in memory, on a hard disk, or some peripheral device, are
always given as some multiple of bytes, like kilobytes, megabytes,
gigabytes or terabytes. Now, kilo-, mega-, giga- and tera- are
prefixes of Greek origin that ordinarily denote quantities in the
thousands, millions, billions and trillions. These are all
decimal or base 10 values, equal to 103 (also known as 10 to the third power, or 10 X 10 X 10), 106,
109 and 1012, respectively. But a kilobyte is a binary value
equal to 210, or 1024 in base 10, and only roughly equal to 1000.
The similarly roughly equal values megabyte (220), gigabyte (230) and
terabyte (240) are 1,024,576; 1,073,741,824; and 1,099,511,627,776;
respectively, as decimal values.
If you've followed along all the way to this point, embrace your inner
nerd, understand that this article only scratches the surface, and do
some extracurricular reading:
Tracy Kidder's The Soul of a New Machine (Little, Brown & Company,
1981) is a Pulitzer Prize-winning, nonfiction account of the design of
a new generation of computer in the 1970s. It's riveting,
perfectly understandable to the uninitiated, and a great way to learn
about computer processors, which haven't really changed all that much.
Wikipedia has fine, long and short articles on the topics discussed here. Try some of the links at the left.
October 26, 2012