What is IPMI?
IPMI is standard which allows remote server management, primarily developed by Intel. IPMI cards, known as Baseboard Management Cards (BMCs) are primitive computers in their own right and are operational all the time, so long as the server has a power source. The server itself does not need to be powered on, or the operating system operational for the BMC to work, it just needs a power source to be connected to the server.
The primary benefits of IPMI are:
View server chassis and motherboard sensor output remotely, such as chassis status and intrusion detection.
Ability to remotely power on, power off, reboot the server and flash the identification light.
Ability to set up a console on a serial port and have the BMC redirect that console over a network port, which in cooperation with BIOS level console redirection, gives you the ability to view the BIOS, bootloader, bootup and shutdown procedures and console output should the machine hang or lock up, just as you would if you were interacting with the machine locally. This is called Serial Over Lan (SOL) and is available in IPMI v2.0 as a standard and using non-standard proprietary methods in v1.5.
Essentially, IPMI will save you from a few hundred to over a thousand GBP instead of buying a remote power control unit and SOL will save you the same amount again over buying an IP KVM.