Comment by userbinator
6 days ago
Remarkably, sending this entire mixed-data byte directly to system port 61h, which historically manages various low-level motherboard controls, does not disrupt the system. In standard DOS environments and modern emulators, pushing these extra bits to the port is effectively harmless.
If anyone is curious what the other bits do and how the PC speaker really works:
https://fd.lod.bz/rbil/ports/keyboard/p0060006f.html#table-P...
https://forum.vcfed.org/index.php?threads/pc-speak-technical...
...and I wouldn't be surprised if some chipset put more hazardous functionality in those reserved bits.
I tested this on a real FreeDos based notebook and it survived ;) But seriously, on more modern systems it doesnt do anything harmful anymore, while i have read that on older systems, you could provoke a system crash this way. Which then would create the interesting task of designing the CA in a way that it "avoids" the hazardous values. For now it seems that "anything goes", at least on all my semi-old and newer systems. DosBox Emulators literally dont care ;)