Atm ,what Are They Doing?

I WAS JUST WONDERING ABOUT ATM MACHINES AND COULD NOT GET WHAT THEY ARE ACTUALLY DOING .
I HAVE AN ACCOUNT IN A BANK A(SAY) AND ONE IN B I GO TO AN ATM OF BANK A AND
GET 2000 INDIAN RUPEES OUT(INITIAL BALANCE WAS 20000) NOW I GET MY BIKE AND GO TO ANATHER ATM INSERT MY CARD AND WHEN I CHECK BALANCE IT WAS 18000 RS (THAT IS 20000-20000=18000).
HOW DO ATM KNOW THAT I HAVE WITHDRAWN 2000 RS 30 MINUTES AGO?
THE MOST PROBABLE ANSWER IS THEY HAVE NETWORKING OF SOME KIND BETWEEN ATM'S OF BANK A.

NOW AT THIS POINT I HAVE 18000RS IN MY ACCOUNT I GO TO BANK B WHICH IS A BANK WHO ACCEPT CARDS OF BOTH A AND B BANK'S.I AGAIN INSERT ATM CARD OF BANK A AND CHECK MY BALANCE IT IS 18000----------------

WHAT IS GOING ON HERE.
IF IT IS SOME KIND OF NETWORKING THAN IT MUST BE SOMETHING LIKE WIRELESS NETWORKING BECAUSE I CAN NOW SEE A MOBILE ATM MACHINE ON INDIAN ROAD'S.

IF ANYONE CAN GIVE ME SOME LINK ON THIS TOPIC I WILL BE THANKFUL .

ok... dude, let me help you out here... skip the caps.

yes the caps don't help.
i don't think bank would be using wireless for that sort of data. that's about as much input as i can give for now. i don't know much bout bank systems but i don't see them using wireless. network yes, but something more secure maybe.

Very simplistic but this might help: http://www.howstuffworks.com/atm.htm

BTW, posting things in caps doesn't get your post answered any faster nor does it make it stand out. I suggest you read the AO Member FAQ found here

Banks are networked, specilally atm's . atm useds to be interconnected throug x25 and then they migrated to ip... ip allowed them much more flexibility... but lacked the security (physical &soft) of x25, or frame relay.
In morocco, societe general uses wireless networking to link all traffic to their central. i will not talk about their security measures but they were very worried about data integrity...