To help us out, where did you find such "literature"?
The "literature I refer to are a variety of sites I was directed to by Google when I performed a search for "IBM T40 HDD Upgrade." As I recall most it was "historical" stuff; recaps of the T40's history. But, in several articles of that type they all made mention of how IBM only offered up to 80GB on their HDDs for the T-40. Being completely in the dark about most stuff "cyber," I figured there must be some limitation for T40's with respect to their HDDs. Perhaps the processor can't handle anything more than an 80GB HDD? Again, you're talking to someone who needs the 1st grade version of any explanation.
Ultimately, what I'd like to do is upgrade to a 250GB HDD that runs at 7500 (or faster) RPM and uses SATA technolgy instead of ASA (which I have now with my current 40GB HDD). Yet, again, I have no clue as to whether or not I can upgrade to a drive that runs faster or one that supports SATA. Will the other components of my system accept those differences?