Yeah, IRQ7 was also pretty common for sound cards as long as you didn’t need to print at the same time. For DOS games, that wasn’t a big deal but if you were running Windows and multitasking with something that played sound (I was an early adopter of MP3s), you couldn’t use both at the same time.

My first Pentium PC was all kinds of awful because it used that IBM Mwave combo sound card /modem. You couldn’t use the modem and play sound at the same time or it would lock the PC up. It was also configured by default to use IRQ7, so if you were online, you couldn’t print either. At least I was able to work around the latter by setting it to IRQ5.

Because I could play the same copies of the same games on my Tandy 1000, the IBM PCs at school, and my friend’s Packard Bell. Standardized architecture was, and still is, a huge draw.

How did PCs beat out the Amiga, Mac and ST with nonsense like that?

I think you can ultimately blame Compaq. It was the first “pc clone” that showed the market that a PC not from expensive IBM was viable. After that even if you weren’t buying a Compaq your own generic clone was “good enough”. So You could access hardware and software built for a $4000 8088 IBM PC with your $1200 clone.

Amiga never was commodity hardware. It was always expensive. It didn’t get cheap enough fast enough. Amiga 500 came too late.

Open and documented APIs.