Back when I first started listening to music - in the days before there were CDs - if you were cool you bought your music on records, and then taped them onto 90-minute cassettes. You did this because it was hard to flip a record while you were driving, records wore out, and pre-recorded cassettes sounded a bit like a 48kbs MP3 stream, when they worked. Sometimes they didn't, and you had a $8 cassette afro.
Oh, and you had to worry about azimuth (an adjustment that, when wrong, could kill all your high end), Dolby B, and, if you were really cool, Dolby C (twice the Dolby!).
And you listened to what was called "album rock" in my area, otherwise known as "progressive rock". Those who wish to debate the differences between those two labels are welcome.
Then, I went off to college, and CDs were released, but the cost $900, so nobody had one (actually one guy in my dorm had one, connected to his $10K high-end system). So, we kept buying albums.
Then prices came down, we got jobs, and we bought CDs of the groups we had listened to, and reveled in the CD experience. The sound was so much clearer than cassettes, that we didn't realize that a lot of the early transfers were awful.
Over time, many of our albums got remastered - first by Mobile Fidelity Sound Lab (who had made some pretty killer vinyl recordings), and then by the labels as they realized there was some money in it.
By this point, you're wondering if there is a point, or if it's just an onion belt.
Anyway, I have a fair number of CDs that are early transfers, and I'd like to replace them, but it can be a bit of a pain to find out what specific albums have been remastered, when they came out, etc.
Enter Progrography, which has a bunch of information about progressive rock, including re-releases. So, if I want to know what remaster to get for Who's Next, there's a page that gives me all the info. Well, some of the info - some of the pages are a bit out of date - but what's there seems to be pretty good.
And if not, I can remember listening to AC/DC, which was the style at the time...