Not intending to bash hal further, but I was just checking out Intel's LessWatts.org site (http://www.lesswatts.org
) and they refer to hal...
hal cdrom polling
One component of the hal daemon (hal is a core component of the various desktop environments and deals with all sorts of hardware interaction) is the part where it polls the cdrom drive regularly (as often as once every 2 seconds!) to see if the user has inserted a CD. This is used, for example, to automatically open a new window with a file browser for the CD.
Such regular polling will keep the hardware awake somewhat; the amount of power consumed depends on the exact type of CDROM drive. It also depends on the presence of the ALPM feature.
If you rarely or never insert CDs (for example because the machine in question is a server 3000 miles away), you can save some power by stopping this polling.
Current versions of hal have a special command for this:
hal-disable-polling --device /dev/scd0
Note that this obviously means that you will not get a popup window if you insert a CD after all. To enable this polling again, you can use the following command:
hal-disable-polling --device /dev/scd0 --enable-polling
Newer SATA based CDROM drives have the capability to notify the machine when a CD gets inserted, making polling not needed. Both the kernel and hal are currently undergoing development to detect and support this capability, so that no polling is needed at any time for these devices.
That last bit is very interesting to me, I will be looking into it and, if possible, add support for that in vl-hot.