How does IPMI work?

I am looking into a new supermicro server and deciding whether IPMI is needed or not. If it does what I think it will be very useful, but I can't find a lot of details on it. Can anyone answer a few questions?

- Does it require software on the server or does it operate below/beside the OS? I will be running VMware ESXi on the machine, so installing other services is a problem.

- If the OS on the host is hosed (blue screen) can IPMI be used to reset the machine?

- What app do you use to manage the machines via IPMI?

the IPMI card is an addon card that allows independant control of the machine at hardware level. I have an AOC-SIMLP-3+ on my X7DBE+. You use software that comes with the card to view the status of the server. It shows voltages, temps, fan rpm, KVM-over-LAN, and virtual media (you can load a virtual cd). The card has its own cpu and memory that run independant of the server. This card can turn on, off, or reset a server. Even if the OS is locked up on the server. Only stipulation is that there must be power to the server, obviously. Its been very handy. The kvm shows you everything that would be displayed on the console if you had a monitor attached, and your keyboard and mouse function the same way. Really handy for changing BIOS settings and configuring hardware raid controllers remotely. Definetly a worthwhile investment. I use my server as an ESX host, so this has definetly been handy for remote upgrades.