https://www.amazon.com/Dissecting-DOS-Code-Level-Operating-S...
The original companion floppy for that is available on archive.org:
https://archive.org/details/dissecting-dos-companion-floppy-...
Understanding Microprocessors is a small book, and currently unavailable anywhere I've seen except for eBay, but it's also normally quite inexpensive.
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https://www.amazon.com/Dissecting-DOS-Code-Level-Operating-S...
The original companion floppy for that is available on archive.org:
https://archive.org/details/dissecting-dos-companion-floppy-...
Understanding Microprocessors is a small book, and currently unavailable anywhere I've seen except for eBay, but it's also normally quite inexpensive.