/ad_da              Some AD and DA convertors (covox and stuff).
/bios               BIOS related info, including some common passwords.
/hd-info            Harddisk info, FAQ's and apps.
/help               Some nice (but old) help apps. Contains much info about
                    interrupts and ports).
/memory             Info about SIMMS and stuff.
/modem              Modem related files.

24lines   .zip      How to make 24 I/O lines for your PC using a 8255 (PDF format).
386bugs   .zip      Test app with source for the old 386 bug (oops, mine had one!).
3dgfxfaq  .zip      PC 3D Graphics Accelerators FAQ.
586bug    .zip      Pentium-bug tester (incl. source).
ddkit     .zip      PC Device Driver kit (incl. some device driver template sources).
ethernet  .zip      Ethernet FAQ.
fast550   .zip      Fast serial ports & 16550 uarts.
ic8259A   .zip      8259A Interrupt Controller on the PC (FAQ).
mc146818  .zip      Real Time Clock (RTC) MC 146818.
overfaq   .htm "Overclocking" FAQ version 0.5.2.
overfaq   .zip      Zipped overfaq.htm.
pc_reset  .zip      News article about resetting the PC.
sb_vol    .zip      Speaker to Sound Blaster Amplifier Converter.
stdlib    .zip      The UCR Standard Library for Assembly Language Programmers.
svga-faq  .zip      PC-hardware-faq/supervga-programming.
vid_grab  .zip      Schematic and source for bad video grabber.

Also see the /ports/pc directory for info about many PC ports !!
Also the /misc/text_cir/f_asci3.htm page.
Looking for pinouts? Or maybe the Hardware Book is better.