In our Company They are planning to go for Cisco CAT 6500 Series Switches with WS-SUP-720 3B.
My ? is
what is SUP
Its the supervisor module.
why we need ??
It holds the IOS/CatOS image and controls the other cards making the switch functional. Also holds the primary memory and gives you console access to the system.
Without SUP we cant run switch or what ?
Correct, and considering the cost and functionality of the 6500 series, why would you ever want to use it as a normal switch -cisco makes plenty of normal layer 2 switches for a tiny fraction of the cost of a 6500. A 6500 can control switching, routing, IDS, and firewall in a single device depending on the modules you install.
Think of the supervisor module as the CPU of the 6500. You can plug all sorts of cards into your PC and probably get them to power up, but they aren't going to do a thing until you put the CPU in.
The other modules may have their own CPU, memory and IOS image as well, if they require it (eg: pix module, ids module)