Magnetic Stripe Equipment
Magnetic stripe equipment has many shapes, sizes, and methods
of mechanical operation. The two fundamental requirements are
that the magnetic "head" must remain in contact with
the magnetic stripe and must remain in motion with respect to
the stripe during reading or encoding. Constant speed is not
required, but zero speed is not allowed. This relative head/stripe
motion may be provided manually (as with a "swipe"
or "dip" reader), or by a motor (as with ATM or transit
ticket transports). The conditions of a given application, including
relevant human factor, determine which approach is preferable.
In addition to the mechanical card carrier and the magnetic
head "transducer", magnetic stripe equipment must
also contain certain control electronics. An encoder must provide
for the proper placement of the digital signals which represent
the string of "zero" and "one" data bits
encoded on the stripe. A reader must provide for transformation
of these digital signals back to the string of data bits. If
the data communications interface of a reader or encoder consists
of such bit strings, it is called a "Bit & Strobe"
unit, and with strobe referring to a clocking pulse used to
clock each bit in or out. These are the minimum capabilities
which a magnetic stripe reader or encoder must have. A "complete"
reader or encoder also provides the additional electronics and
software required to manipulate the various encoding data formats
(analogous to symbologies in bar code), perform error checking,
and communicate in ASCII characters.
Data storage and retrieval
Digitized data is stored by altering the polarity of tiny particles
embedded in a resin. The card data is encoded in a binary format,
with the polarity of the particles determining the 0-bits and
1-bits. A reader detects and decodes the polarity changes, called
"flux reversals," and translates the binary code to
alphanumeric for processing by a computer.
The technology involves a special digital recording (called
"encoding") of data on a magnetic layer (called a
"stripe") similar to that on audio and video tape,
which can then be repeatedly played back (called "reading").
A principal feature of magnetic stripe is that it can be re-encoded
and used over again. This feature is crucial in many applications.
Magnetic stripe media
The diversity of cards, badges and tickets which contain the
magnetic stripe are called "media." They must be made
of virtually any non-magnetic material which will maintain the
structural integrity of the stripe. The most widely used materials
are paper, coated or plasticized paper, PVC plastic, and PET
plastic, in order of increasing durability. The most widely
used size is that of the standard credit card. The magnetic
stripe may be bonded to the material in various ways, but must
be on the surface so that nothing separates it from intimate
contact with the magnetic head. One edge of the media must be
straight and parallel to the direction of encoding on the stripe,
to serve as the locating reference for the read and encode heads.
Data robustness
Data robustness is an issue with magnetic stripe technology,
because the encoded data is susceptible to accidental damage
by magnetic fields. Coercivity is the term used to designate
how strong a magnetic field must be to affect data encoded on
the stripe, and, therefore, how immune the data is to damage.
Measured in Oersteds (Oe), the coercivity of a common credit
card is about 300 Oe, considered low coercivity (nicknamed "LoCo").
Consequently, magnetic money clips, refrigerator magnets, etc.,
can damage the data on your credit card's stripe. High coercivity
(HiCo) magnetic stripe technology relies on particles - generally
barium ferrite (low coercivity uses iron oxide) - with coercivity
values ranging from 2500 to 4000 Oe. The encoding technique
is the same as for LoCo technology, except that it requires
a stronger electrical current in the write head. Virtually immune
to domestic-type magnets, HiCo substantially decreases the chances
of accidental data erasure. Despite this superiority, HiCo hasn't
yet replaced LoCo technology, due to the widely established
base of LoCo encoders and the increased cost of HiCo encoders.
Standard magnetic stripe readers, however, can read either HiCo
or LoCo stripes. High-coercivity cards are currently used in
applications where the need for performance, for example in
critical test equipment, outweighs price.
Magnetic stripe tracks
A single magnetic stripe can hold several tracks of recorded
data, which can be rewritten and updated. The ISO/IEC 7810,
11, 12, and 13 series of standards specify a three track format,
encoding scheme, and bit density for all financial card applications.
The narrow band on the magnetic stripe running parallel to this
reference edge and on which data is encoded is called a "track."
It is typically about one-tenth of an inch wide and may be located
at any distance from the reference edge. The possible number
of such tracks is thus determined entirely by the width of the
stripe.
Standards exist for many track locations, the best known being
ISO Tracks #1, #2 and #3 on credit cards. The widest range of
equipment is available for these tracks. The ISO credit card
data densities and formats are also the most widely used, yielding
42 Binary Coded Decimals or 30 ALPHA characters per inch at
210 BPI, and 15 BCD characters per inch at 75 BPI. It is important
to note that the magnetic stripe is not limited to these credit
card track locations or data densities and many others are in
common use.
Reprinted with permission from AIM, Inc.
www.aimglobal.org
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