Laptop hard disk drives
Fucking laptop drives make SCSI look simple. At least with SCSI each flavor *does* achieve backward compatibility and the nomenclature can easily be reduced to the bus speed.
But this IDE crap and son of a bad idea known as SATA ? Well, they're cheap, I'll give them that much.
Laptop drives are either SATA (most now) which are all compatible with the I, II and II flavors of SATA.
Then we have "other". Which really means "IDE". Which is really the command set for the Seagate ST506 5" full height disk drive, a wretched beast at best.
But it also gets called PATA, EIDE, ULTRA, ULTRA DMA, ULTRA 100/DMA, ULTRA 66/DMA, IDE, ATA and Christ knows how other many flavors and names they've cobbled up for these drives.
Wikipedia actually has the best treatment of the subject and a nice table that explains ATA-1 through ATA-5 and ATA-6, the latter being the latest and contemporary standard at time of writing. ATA-5 drives are still around, SATA picks up where PATA gets stuck so really the emphasis these days is on SATA and PATA drives are becoming more scarce as less are made each year.
But, to somebody with a laptop that needs PATA, not SATA drives, this doesn't matter.
While on first inspection $33 for a 160GB laptop drive seems appealing, this being the most gigs for the least dollars on pricewatch.com, you have to also look at rotational speed of the drive, these can come in 4200, 5400 and 7200 rpm models, and if your machine happened to have come with a 7200 rpm drive, like mine seems to have, you're not going to be happy with the performance of anything else. Of course 4200 rpm drives are the cheapest, 5400 rpm drives the most common and 7200 rpm drives nearly 3X the price of equivalent slower dives in some cases.
As of the time of writing (and this may change by next week of course) SSD - Solid State Drives - bunches of memory chips that replace the spinning platter in a hard disk, are not cost effective. For $10 more than the most economical SSD drive you get 10X the storage with a hard drive. While this is true, there are still some marginal cases, for example a hihg speed 7200 rpm drive in the 30GB range is about $90 and a 32GB SSD drive can be had for $150. The gap is narrowing and will continue to do so in a very predictable manner.