I want to add a bigger SECOND HD but im a little unsure about compatibility.
example-
Ultra ATA 133 / ATA 100
EIDE/IDE
2MB/8MB/16MB
 5400/7200/7200.10

What do I need?
I currently have an OEM 40gig and an old 13gig for a slave.Any EIDE/IDE should work, but you should be aware of Hard Disk Size Barriers.  You may encounter this: The ATA Interface Limit (128 GiB / 137 GB) BarrierMy motherboard is not very old and my bios is the latest release so size is not a FACTOR, I just want to spend under 100bucks.
Im looking at these two pages
Serial ATA
http://www.tigerdirect.ca/applications/category/category_slc.asp?CatId=139

Internal IDE PATA
http://www.tigerdirect.ca/applications/category/category_slc.asp?CatId=134

Internal SCSI- this stuff is just too expensive
http://www.tigerdirect.ca/applications/category/category_slc.asp?CatId=135&


My motherboard model is in my sig - http://www.asrock.com/product/P4VM800.htm
Heres the highlights-
Socket 478 for Intel P4 processor
VIA P4M800 chipset
Supports FSB800MHz processor, Prescott
Ready and H-T Technology
2 DDR DIMM slots, Supports DDR400/333/266
Hybrid Booster - ASRock safe overclocking Technology
SerialATA 1.5Gb/s, SATA HDD_Hotplug, RAID 0,1,JBOD
AGP8X, 5.1channel Audio, 10/100 Ethernet LAN
ASRock I/O Plus: 6 ready-to-use USB2.0 portsSATA has faster transfer speeds than IDE...but can be a chore to SETUP sometimes.

All IDE manufacturers make decent drives so don't get caught up in the WD vs. Maxtor vs. Seagate arguments ...they are a waste of time.

Seagate just acquired Maxtor but are also the only manufacturer offering 5 year warranties if that's important...

Basically when i buy HDD's i just try to get the most bang for my buck.

patio.   8-)

p.s. and always remember GX1_Man's maxim....all HDD's fail eventually. DEVISE a regular backup strategy.OK then, thank you