Difference between system standby and hibernation

What is the difference between system standby and hibernation?

In standby/sleep, the power is kept on to the memory, the processor is bought to a stop and devices are put into low power mode. However there is still some activity as the memory still needs to be refreshed (otherwise it looses its contents) and the low power mode of devices may not be all that low. Unplugging the computer from the mains (or removing/flattening the battery) will result cause a cold reboot with possible data loss. Startup from standby is very quick as the devices need to be woken and the CPU restarted.

In hibernate, the memory is written to the hard disk (in the hiberfil.sys file), along with the state of devices and the CPU and then the power is turned 'off'. The computer is still burning a little power as things like keyboard/mouse/LAN power on features are supported. However, unlike standby, unplugging the computer from the mains doesn't result in a col boot or data loss as everything needed is stored on the hard disk. Startup is still pretty quick as the memory needs to be read from the disk, the devices reactivated and the CPU restored to the same state is was when the hibernate started.

Vista goes one step further with its 'hybrid sleep' mode which writes all the same stuff to the disk as a hibernate does, but then keeps the system in standby mode. If the power hasn't been interrupted then the restart is the same as a standby restart, or if the power has been interrupted then a warm boot from the hibernate info on the hard disk is used.

However, almost all computers are never completely turned off unless the power/battery is removed. PC power supplies have a special power lead to provide 'standby' power that is always there even if the computer is 'off'. It doesn't matter if the computer is in standby, hibernate or a full shutdown, that standby power is still there. This means the power supply is still alive and chewing power.

Most ATX power supplies have a kind of efficient 'baby' power supply built in to supply this standby power when the main power supply is off. However I had one very inefficient power supply that drew nearly 60 watts even when the computer was fully shutdown! I'd say it didn't have this baby component and used the main power supply circuit all the time. I've since 'retired' that power supply!

So to answer the original questions "is this what some people mean when they say they never really turn their computers off?"

Basically yes.

Does hibernation consume any power whatsoever?

Yes, although often (but not always) it is a relatively small amount of power (20 watts or so).

Put your hand on the case above the power supply of a computer that has been off for a while and you will often still feel warmth as the PS supplies the standby power.