5/2/99

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When buying a hard drive, regardless of IDE or SCSI, you need to
look at the technical specs.  Why?  Hard drives have changed quite
a bit in the last few years.  

What changed?  The main changes are the transition from thin 
film heads to IBM's Magneto-Resistive and now Giant 
Magneto-Resistive heads and also the migration from standard 
analog head interface electronics to DSP-based interfaces.  These 
two changed are the main drivers for the disk cost and capacities 
we're seeing today.

Ok, so all 8GB IDE 5400RPM hard drives are the same right?  No!
Again.. you need to look at the technical specs of the drive and
figure out what a given disk's transfer rate is.  When you are
looking at a hard drive's specs, look for the "internal transfer
rate".  Typically this spec will be given in two different numbers.

	NOTE:  Some manufactures use Megabit/s (Mb/s) while others
		use MegaByte/s (MB/s).  Make SURE you do the 
		conversion before doing any comparisons:

		   MB = Mb / 8

	NOTE 2: The lower of the two transfer rate numbers is for 
		 the hard drive tracks closest to the spindle and 
		 the higher number is the tracks away from the 
		 spindle.

		- Why?  Think of a spinning bicycle tire.  The 
		  center hub spins slower than the outer tire.  
		  Because of this, more data can be read off 
		  the outside tracks than the inner tracks for 
		  a given amount of time.


So, with this knowledge in hand, you'll notice that some drives are
significantly SLOWER than other drives.  Beware!


Other things that differentiate hard drives:

	- Interface 			(IDE vs. SCSI)
	- RPM 				(faster is better)
	- head seek time 		(lower is better)
	- built-in cache size 	(bigger is better)

--David