Originally posted by: Lord Evermore
I think Intel's VIIV design has an "Instant On" part of it which claims to be putting your computer into a standby mode for quick turn on, but when people looked at it it turned out all it was doing was turning off the monitor.
Even if you don't have a VIIV machine, that may be all that you are actually doing. You will need to check your motherboard manual for the settings related to power management, and ensure that the proper suspend modes are enabled. There are various levels of "sleep" which shut down certain hardware, your system may be keeping the CPU fan or power supply fan running. There is a standby mode which doesn't shut very much off, and then "suspend to RAM" which halts all processing and turns off everything except the memory modules, and when you start the computer it just loads back up as if it was never shut down. The manual should tell you how to make sure that "S3" mode is enabled, or "STR", suspend to RAM.
Does the system actually keep working the hard drive or is it just the fans that you're hearing? Can you tell if the hard drive is still spinning? (You can open the case and just feel the drive while it's on, and then compare to what it feels like in suspend.)
Hibernation mode is the best mode for conserving power and reducing heat output. This actually shuts down the entire computer. When you hibernate, the OS stores a copy of the RAM on the hard drive and then turns off the computer. When you boot, the OS always looks to see whether it was put into hibernate mode; if it was hibernated, it reads the hibernation file, if you just did a shutdown, it just boots normally.
Here is a description of the various modes. It sounds like your system may be only going into S1 mode.