http://margo.student.utwente.nl/el/
pc

/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      Comp.sys.ibm.pc.hardware.chips "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.