Changes

*[https://bitsavers.org/pdf/ibm/pc/GG24-3057-00_IBM_PC_Internals_Fundamentals_Course_Notes_198603.pdf IBM PC Internals Fundamentals Course]

*[https://bitsavers.org/pdf/ibm/pc/pc/6025008_PC_Technical_Reference_Aug81.pdf IBM PC] [http://bitsavers.org/pdf/ibm/pc/pc_jr/PCjr_Technical_Reference_Nov83.pdf IBM PCjr] [http://www.retroarchive.org/dos/docs/ibm5160techref.pdf IBM PC XT] [https://bitsavers.org/pdf/ibm/pc/at/1502494_PC_AT_Technical_Reference_Mar84.pdf IBM PC AT] Hardware Technical Reference

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