The IBM PC/XT? It runs Unix.
The IBM PC/XT was an upgraded version of the original IBM PC, adding a 10 MB hard drive - which, for 1983, was a pretty good amount of storage. Originally, it shipped with PC-DOS, but soon after release a couple of Unix variants became available.
The first variant was PC/IX, which came on 19 floppy disks and was accompanied by an 1,800-page manual. Due to hardware constraints, various features are missing from this system - there's no FORTRAN compiler or TAR, no BSD tools such as vi (the INed editor takes its place) or the C Shell. Despite achieving reasonably good performance, it was not a commercial success.
Released in 1983 by SCO, Xenix was Microsoft's own variant of System 7 Unix. It ran on a variety of 16-bit micro- and minicomputers and it featured Microsoft's own improvements to the base OS. Microsoft licensed the OS package to various corporations, who were then expected to port it to their own architectures themselves. SCO developed the IBM PC port, adding in various improvements from BSD 4.2. Unlike PC/IX, Xenix featured vi, as well as termcap and curses, and it also supported rudimentary networking through serial ports. It was also the first multi-user, multitasking OS on the platform.
Minix was developed from the ground-up as a fully-compatible Unix variant by Andrew S. Tanenbaum, who used it to teach concepts on operating system design. Coming in at 12,000 lines of code, it was fully compatible with Seventh Edition Unix system calls. The concepts behind Minix were explained in the accompanying textbook, Operating Systems: Design and Implementation. Minix is also historically significant as the OS Linus Torvalds was using when he started work on his own Unix-like kernel, Linux.
PC/IX was quietly discontinued and replaced with 386/ix, or Interactive Unix in 1985. Xenix survived until 1989, when it was replaced by SCO Unix (now SCO OpenServer). Minix is still being actively developed, and it went open-source in 2000.
