|
|
|
Door Entry Panel Mounted Reader
|
Click here to download the PDF file of this document Magnetic
Stripe Cards (All
you ever wanted to know and some you didn't) written
and compiled by John KayApril 1995 (updated April 2000)
There
is frequently confusion, doubt and even misinformation surrounding the humble
magnetic stripe card. The following
is a comprehensive guide to technical aspects of magnetic stripe cards, it is my
attempt to divulge all the facts (as far as I know them and can uncover them, so
please use this information with care). Background Magnetic
stripe cards are without the most widely used cards in the world, both in access
control and banking and have been around since the 1960's.
While other card technologies are forging ahead and gaining wide
acceptance the magnetic stripe card, due to the shear number of bank cards,
credit cards, loyalty cards and the like is still by far the most widely used
card world-wide. Standard
magnetic tape is available from many sources and is similar to audio or
videotape. High Coercivity is
generally agreed to be of a value of 4000 Oersted.
The 3M company is the major supplier of 4000 Oersted tape.
Other manufacturers produce tape of 3500, 3000 and even 2750 Oersted that
are all considered High Coercivity (Hi-Co).
For access control applications 4000 Oersted tape is generally the best. The coercivity is the value of coercive force for a substance that has been initially magnetized to saturation or more simply put its a measure of the magnetic force required to change the state (orientation) of the magnetic material. Hi-Co cards require up to 13 times the force of standard cards and as a result, they are immune to stray magnetic fields and are unlikely to be accidentally erased or corrupted. A
magnetic stripe card that conforms to the ISO standard can be either a standard
300 Oersted stripe or a high coercivity 4000 Oersted stripe.
Bankcards currently use 300 Oersted tape to form the magnetic stripe.
How
is the data physically encoded on to the magnetic stripe? The
magnetic tape used on a standard magnetic stripe card is similar to the tape
used in audio and video cassette tapes. A
magnetic oxide is dispersed on to a thin plastic PVC card and bonded to its
surface.
On
track 2, each data bit is 75ths of an inch in length. A data 0 bit has the magnetic field aliened in one direction
(the direction is not important) for a length of 75ths of an inch.
A data 1 bit has a reversal of the magnetic field in the middle of the
bit. There is also a reversal in
the magnetic field at the edge of each bit. (See figure above). The
stripe or tape is divided in to three tracks according to ISO 7816 as follows: Track
1 Track
1 was specified by IATA, is a read only track and is seldom used.
Some banks use this track and encode the card details and the cardholders
name. Track
1 is encoded at 210 bits per inch and 7 bits per character (including parity),
giving 79 alphanumeric
characters. This track is read
only. The
six data bits allow characters 0 - 9, A - Z and a few others characters such as
@ = * % ( ) - / .
The seventh bit is odd parity.
(a) These
characters are available for hardware control purposes only. (b) These
characters are reserved for additional national characters. (c) Reserved
for additional graphic symbols. (d1) Start Sentinel (d2) End Sentinel (d3) Separator
Track 2 Track 2 was originally specified by the American Banking Association (ABA) and is without doubt the most widely used track. Most access control systems that handle magnetic stripe cards use this track. Same companies use as a selling point the fact that any card encoded to ISO format can be enrolled into their system. i.e. They can use bank cards or credit cards. Track 2 is encoded at 75 bits per inch and 5 bits per
character including parity, giving 40 numeric characters.
Track 2 is a read only track. Each character consists of 4 data bits plus a parity
bit. The order of the digits is
normally: Start
Sentinel 1 Character
Card
Data up
to 37 numeric characters Stop
Sentinel 1 Character
LRC
1 Character Longitudinal Redundancy Check (LRC) is an even parity
check on all characters, so that all characters including the LRC
bit have an even parity. Data Characters include parity and are: Parity
Data Character 1
0000
0 0
0001
1 0
0010
2 1
0011
3 0
0100
4 1
0101
5 1
0110
6 0
0111
7 0
1000
8 1
1001
9 1
1010
Reserved 0
1011
Start
Sentinel 0
1100
Reserved 0
1101
Separator
0
1110
Reserved 1
1111
Stop Sentinel
The reserved characters are not used in credit cards,
but might be used in Access Control cards. For example an ISO card number of 8902042311 is encoded on
Track 2 in binary would be as follows: 01011 01000 11001 10000 00010 10000 00100 00010 10011 00001 00001 11111 1 Track 3 Track 3 was originally specified by Thrift Industries
and Mints, the intended use was for cashless vending.
The track is a read/write track and as far as I am aware it is used by a
number cashless vending companies and by some Banks’ ATM's to write
information about the last transaction, such as the amount of money withdrawn
from the account on that day. Track 3 is encoded at 210 bits per inch and 5 bits
per character including parity, giving 107 numeric characters. These are the same as track 2 except that this track is used for read and
write. SCALESTo
give some idea of the physical properties of the standard low coercivity tape we
present the following information. It
is intended to be indicative only and therefore the actual sizes may be different
in reality. The particles are
aliened length wise along the length of the track. Approximate size of a single Fe2O3 Particle
compared to the wavelength of yellow light Approximately 40 times the width of an A4 page |
