> The single-ended drives (50 pin)

"Single-ended" and "50 pin" have nothing to do with each other. It's like
saying "blue (size 10) dress"; both attributes may appear on a particular
item, but they can also both be combined with alternate values of the other
attribute.

> The first digit is the height (1= half-height, 3= Low
> Profile).  The next 2 (or 3 digits)  refers to the
>  capacity (43 =4.3GB, 45=4.5GB,  91=9.1GB, 182=18.2GB, etc. ).

Actually, for Seagate model numbers all digits after the first (at least
until you run into some letters or punctuation) are the capacity. And the
first digit is a form factor, not just height, identifier:
  1 - 3.5in half height (1.625in)
  2 - 5.25in half height
  3 - 3.5in low profile (usually 1 inch high)
  4 - 5.25in full height
  9 - 2.5in portable-computer drives, mostly in the 17mm height

There are various others, mostly obsolete; see
  http://www.seagate.com/support/kb/disc/discmodelinter.html
for a full explanation of Seagate and Connor model numbers.


Steve