About two hundred years before, the word "computer" started
to appear in the dictionary. Some people even didn't know what is
a computer. However, most of the people today not just knowing
what is a computer, but understand how to use a computer.
Therefore, computer become more and more popular and
important to our society. We can use computer everywhere and
they are very useful and helpful to our life. The speed and
accuracy of computer made people felt confident and reliable.
Therefore, many important information or data are saved in the
computer. Such as your diary, the financial situation of a oil
company or some secret intelligence of the military department. A
lot of important information can be found in the memory of
computer. So, people may ask a question: Can we make sure that
the information in the computer is safe and nobody can steal it
from the memory of the computer?
Physical hazard is one of the causes of destroying the data
in the computer. For example, send a flood of coffee toward a
personal computer. The hard disk of the computer could be
endangered by the flood of coffee. Besides, human caretaker of
computer system can cause as much as harm as any physical hazard.
For example, a cashier in a bank can transfer some money from one
of his customer's account to his own account. Nonetheless, the
most dangerous thief are not those who work with computer every
day, but youthful amateurs who experiment at night --- the
The term "hacker "may have originated at M.I.T. as students'
jargon for classmates who labored nights in the computer lab. In
the beginning, hackers are not so dangerous at all. They just
stole computer time from the university. However, in the early
1980s, hackers became a group of criminals who steal information
from other peoples' computer.
For preventing the hackers and other criminals, people need
to set up a good security system to protect the data in the
computer. The most important thing is that we cannot allow those
hackers and criminals entering our computers. It means that we
need to design a lock to lock up all our data or using
identification to verify the identity of someone seeking access
to our computers.
The most common method to lock up the data is using a
password system. Passwords are a multi-user computer system's
usual first line of defense against hackers. We can use a
combination of alphabetic and number characters to form our own
password. The longer the password, the more possibilities a
hacker's password-guessing program must work through. However it
is difficult to remember a very long passwords. So people will
try to write the password down and it may immediately make it a
security risk. Furthermore, a high speed password-guessing
program can find out a password easily. Therefore, it is not
enough for a computer that just have a password system to protect
its data and memory.
Besides password system, a computer company may consider
about the security of its information centre. In the past, people
used locks and keys to limit access to secure areas. However,
keys can be stolen or copied easily. Therefore, card-key are
designed to prevent the situation above. Three types of card-keys
are commonly used by banks, computer centers and government
departments. Each of this card-keys can employ an identifying
number or password that is encoded in the card itself, and all
are produced by techniques beyond the reach of the average
computer criminals. One of the three card-key is called watermark
magnetic. It was inspired by the watermarks on paper currency.
The card's magnetic strip have a 12-digit number code and it
cannot be copied. It can store about two thousand bits in the
magnetic strip. The other two cards have the capability of
storing thousands of times of data in the magnetic strip. They
are optical memory cards (OMCs) and Smart cards. Both of them are
always used in the security system of computers.
However, it is not enough for just using password system and
card-keys to protect the memory in the computer. A computer
system also need to have a restricting program to verify the
identity of the users. Generally, identity can be established by
something a person knows, such as a password or