Why is Access Control necessary?
Access control is really what the name suggests, a control over who and what is permitted access to a building or venue. It is generally applicable where technology [provides the means of control, as opposed to man power, but even security guards or bouncers outside a club can be counted as a primitive kind of access control.
Early forms of access control in a business may just be staff ID cards. These can then be shown to a person at reception who either accepts them or declines them. You can get more advanced identity cards, with barcodes or magnetic stripes so that there can be information flagged up on screen whenever someone swipes their card. These could also be used in automatic door locking/unlocking mechanisms. Or, more advanced still, you could have a microchipped card, which will hold much more information.
MiFare cards and other proximity cards are by far the easiest and most secure method of access control. They store information, and only need to be held close to the reader to almost instantly permit or deny access. This is fully automated, and so there will be no room for human error in the process.
