MS-DOS was written for only one processor. UNIX kernels could run on a variety of processors, including ARM; UNIX was a relative latecomer to x86. As for Wind

MS-DOS was written for only one processor. UNIX kernels could run on a variety of processors, including ARM; UNIX was a relative latecomer to x86. As for Windows kernels, both then and now, UNIX kernels are open source and do not deliberately obscure system calls. It's not unreasonable for someone to argue the benefits in writing programs for UNIX. "View this page as what it is..." It's one of the few pages written about UNIX assembly. That's how I view it. Years later it was put into The FreeBSD Handbook.