Before you buy a hard drive, make sure that you know what sort of interface you have in your computer.  If you have an older computer like I do, chances are that you still have your hard drive connected via an EIDE interface.  If this is the case and you buy a hard drive with a SATA interface, be aware that it will not work without either some extra adapters or cables.

Case in point: I have a 4+ year old Dell Dimension 8300.  My existing 40 gig hard drive is connected to an EIDE interface.  I just bought a 250 gig Maxtor SATA drive and expected to be able to add that to my computer (not replace the existing drive.)  I went out and read up on it, and the drive manual's illustrations showed an interface that looked like what I had in my computer, EIDE.  When I got the drive, though, the interface was not the same as the illustrations - it was SATA.  It did have both the old style 4 pin power connector and the new style SATA power connector, but the data connection was SATA only.

My next step was to  research what kind of cable or adapter I might need, and then go to the Dell Website and download the manual for my 8300.  The manual told me a couple of things: the motherboard has two SATA ports (great!) but "Do not run EIDE and SATA together" (not good!)

Next I went and ordered a SATA cable, and I then got some disk imaging software, thinking I'd have to move the operating system to the new drive (since I wasn't supposed to run the two types of drives together.)  I wanted to image the 40 gig drive to my Ipod's 40 gig of drive space that was free, but I couldn't get the disk imaging software to recognize any drives on the USB bus.  At this point I put the imaging idea on the back burner, and decided to try hooking up the new drive to the SATA interface and see what happened.

I plugged the drive in to one of my motherboard's SATA ports, enable the port I thought it was in bios, and got a "SATA Drive 0 cannot be found" message when booting up.  Plan B - enabled the other port in bios, got the same error message.  Frustrated at this point, I was almost ready to give up.  A little later that same night, though, I decided to go back to Maxtor's Website and read up on SATA installation and VOILA!  There was a jumper installed in the drive that needed to be removed for SATA operation.  I removed it and then it was back to plugging the drive in and enabling the port.  At first attempt, I enabled the wrong port (50/50 chance - you know how that goes.)  Second attempt, bios showed SATA Hard Drive on the secondary SATA port - SUCCESS!

Next, I booted up into Windows XP to see if the two drive types would coincide.  Contrary to what Dell's manual said, they are coinciding very well.  I didn't even need to do a disk image to transfer the operating system and everything to the new drive.  I formatted the 250 gig, my system still boots from the original 40 gig, and life is good!

Tips for others:

1) If your motherboard does NOT have any SATA ports, there are adapters that you can buy.  Just search eBay or Google with "SATA to EIDE adapter" (or similar) as your search terms.  I can't vouch for how well they work because I didn't need one, but they're out there.

2) On the Dell Dimension 8300, as you look at the motherboard with the front of the computer to your left (where the drive bays are), the SATA port on the LEFT is the secondary one.  I think I lucked out having hooked up to that port.  I'm guessing that if I had hooked up to the primary SATA port, the computer may have tried to boot off the new drive, which would not have worked without having the operating system on it.  In any event, EIDE as primary drive, and SATA hooked up in secondary port as secondary drive works on a Dell Dimension 8300.  And by the way, for drive installation, this particular Dell model has green rails sitting in the empty drive bay that you pull out, screw to the new drive, and then snap the new drive right into the bay - very quick, easy and slick!

3) When I refer to "bios" above, I am referring to your computer's computer-level setup utility, usually accessible by hitting the F2 of F1 key right at the beginning when booting your computer up.  Every computer should have a section in there for configuring the hard drives.

4) Always try it to see if something might work first, before taking extra time and expense to alleviate a problem you think or assume might happen.  In my case, I went out and got disk imaging software that I didn't need.  Luckily I hadn't already burned up a bunch of CD's to make the disk image.

I hope that reading about my personal experience with this will save you some time and headaches!  Good luck!