Linear mode
 

On installing Red Hat 7.1, there is a box:

"Use linear mode (needed for some SCSI drives)"

This is checked by default. I have a Western Digital Caviar 153BA hard disk drive. Should I leave this box checked, or uncheck it?

Assuming it is an scsi drive, then yes, you might as well. actually, it shouldn't make any difference if you include it. It can cause problems running programs like VMware i'ev found.. but that's somethign to think about later, for now, yeah leave it in

it'll just end up as a line in the /etc/lilo.conf file, which you can remove at any time.

i did a quick check up on the caviar drive... i didn't find anything indicating that it's a SCSI drive... the specs i found said it was an ATA/100... but here i have to plead utter hardware ignorance. i haven't the faintest idea of what SCSI is. it's probably safe to leave the linear option out, but i don't think will hurt anything to leave it in.

It is an IDE hard drive.

I've tried it both ways and it *works* both ways...

My question is: Which way would be more optimal?

The linear and lba32 (Logical Block Addressing) options have to do with how your system interprets a large hard disk's geometry. Newer versions of lilo (and newer BIOS's) can deal with the larger drives, so twiddling with the options isn't usually neccessary. I'd suggest that if you don't need to specify linear, leave it out.
You can read more about this in the Large Disk HOW-TO.