I recently purchased a Colt AR-15 SP1.  From the serial number list in this forum and serial number on my AR-15, I can tell that I have a pre-ban AR-15.

Earlier this morning, I was browsing around in the books & Manuals section.  There is a book titiled "AR-15, M16 Assault Rifle Handbook."  The description says, "This book covers the early AR-15, M16, and M16A1 rifles. It is mostly a reprint of the military TM, but in addition includes some history and a few additional tidbits (including some nice illustrations). Recommended if you own one of the earlier AR-15's (M16, M16A1 style) as it contains all the basics."

Here's my question. What constitutes early AR-15, M16 or M16A1?  How do I know which one I have?

I would think that this is important for me to know, especially to make sure that I am using manuals and books that applies to my AR-15.

I would appreciate it very much you could help me sort this out.

Thank you very much in advance.

Post your serial number MINUS THE LAST THREE NUMBERS.

Example SN#1234XXX

Well you don't have an M-16, unless you whent through a tremendous amount of paperwork and mailed a check to the Federal Government.

So its most likely an AR, of one sort or another.

If you have a raised area, or "fence" surrounding your magazine release button then you have an A2, or later model, A3(A2 from factory w/Flattop, but I dont think Colt shipped sp-1's w/A3 config's, not sure though)  AR.  If not, then you have what some call a "slab side" or an "older model" AR  A1 configuration.  
If you have a Slab side, you may still have an upper receiver, that is in the A2 configuration.  IE. round handguards, and most importantly the rear sight. The A2 sight will be marked to 800 meters, and will have 2 adjustment dials, one horizontally, your elevation, the other vertically, your windage.

Some on this board know the differences between Colt's models, when they were released, and the nuances of Colt's models, ie. trigger pin size differences, take down pin size differnces, sear blocks, Blue label, Green label etc. etc.
(Not a "flame", just too much info for my head)
 
But, based on your post it sounds like you need to know if you have an A1 or A2.  The above helps I hope.
Once you've narrowed down A1 or A2 post more info and the guys on this site will get you all the info. you need, and/or some good suggastions on how to get your questions answered.  GDLk, and enjoy that AR, SUL2