The System Management Controller (SMC) is an internal subsystem introduced by Apple Inc. with the introduction of their new Intel processor based machines in 2006. It takes over the functions of the SMU

System management unit

The System Management Unit is an advanced internal subsystem introduced in late 2004 with the iMac G5 and Power Mac G5 series computers. It manages the functions previously governed by the PMU as well as additional cooling functions.-Overview:The SMU manages thermal and power conditions to...

. Apple has released updates for this system in order to address power or sleep issues in several recent models .

Overview

The SMC controls power flow and fan speed, like the SMU before it. The main objective is to keep the machine running normally with a minimum of noise.
The SMC should not normally need to be reset at all. Doing so however can be useful in troubleshooting

Troubleshooting

Troubleshooting is a form of problem solving, often applied to repair failed products or processes. It is a logical, systematic search for the source of a problem so that it can be solved, and so the product or process can be made operational again. Troubleshooting is needed to develop and...

 certain issues.

• Failure to turn on
• Failure to recognize internal AirPort
  AirPort
  AirPort and AirPort Extreme are local area wireless networking products from Apple Inc. based on the IEEE 802.11 standard ....
  
   Extreme card
• Failure to recognize internal Bluetooth Module
• Failure to recognize attached devices (Firewire, USB, etc.)
• Unexpected power off (i.e., sudden unexpected loss of power, not system shutdown)
• Failure to wake from sleep or unexpected sleep (note this can also be caused by operating system
  Operating system
  An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
  
   corruption)
• Failure to recognize keyboard and trackpad

This is due to the fact the SMC may become corrupted over time and not respond properly to certain requests. This sort of corruption can be triggered by a power surge.

Current SMC Updates

	Shipping Version	Updated Version
iMac IMac The iMac is a range of all-in-one Macintosh desktop computers built by Apple. It has been the primary part of Apple's consumer desktop offerings since its introduction in 1998, and has evolved through five distinct forms....  Early 2006	?	1.1f5
Mac Mini Mac Mini The Mac Mini is a small form factor desktop computer manufactured by Apple Inc. Like earlier mini-ITX PC designs, it is uncommonly small for a desktop computer: 7.7 inches square and 1.4 inches tall. It weighs 2.7 pounds...  Early 2006	?	1.3f4
MacBook MacBook The MacBook was a brand of Macintosh notebook computers built by Apple Inc. First introduced in May 2006, it replaced the iBook and 12-inch PowerBook series of notebooks as a part of the Apple–Intel transition. Positioned as the low end of the MacBook family, the Apple MacBook was aimed at the...  Any	?	1.4f12
MacBook Pro 15-inch	?	1.2f10
MacBook Pro 17-inch	?	1.5f10
Mac Pro Mac Pro The Mac Pro is a workstation computer manufactured by Apple Inc. The machines are based on Xeon microprocessors, but are similar to the Power Mac G5 they replaced in terms of outward appearance and expansion capabilities...  2 or 4 Cores	?	1.7f10
Mac Pro Mac Pro The Mac Pro is a workstation computer manufactured by Apple Inc. The machines are based on Xeon microprocessors, but are similar to the Power Mac G5 they replaced in terms of outward appearance and expansion capabilities... 8 Cores	?	1.15f3