Probably Peter Norton's Assembly Language Book for the IBMPC. Ray Duncan's Advanced MSDOS was another essential. If you want a bit more esoteric, The Undocumented PC by Frank Van Gilluwe.

I could name a few more but I probably shouldn't be admitting that I'm pulling these off my shelves :-)

Ah thank you! I currently have the MS-DOS Encyclopedia (not the first first edition https://blogs.msdn.microsoft.com/larryosterman/2004/06/14/do... which was apparently a little _too_ detailed) which is pretty informative. I'll track down your recommendations though.

Oh. Another one is Norton's Programmer's Guide to the IBMPC. Finally, one other book is Brown & Kyle's PC Interrupts.

I sold a shareware DOS file management program written in assembler (the file was about 30kb) for a number of years which is why I have all this obscure stuff :-)