Editing IBM RT PC (section)

==Software==
One of the novel aspects of the RT design was the use of a [[microkernel]]. The keyboard, mouse, display, disk drives and network were all controlled by a microkernel, called Virtual Resource Manager (VRM), which allowed multiple operating systems to be booted and run at the same time. One could "hotkey" from one operating system to the next using the Alt-Tab key combination. Each OS in turn would get possession of the keyboard, mouse and display. Both AIX version 2 and the Pick operating system were ported to this microkernel. Pick was unique in being a unified operating system and database, and ran various accounting applications. It was popular with retail merchants, and accounted for about 4,000 units of sales.

The primary operating system for the RT was AIX version 2. Much of the AIX v2 kernel was written in a variant of the [[PL/I]] programming language, which proved troublesome during the migration to AIX v3. AIX v2 included full [[TCP/IP]] networking support, as well as [[Systems Network Architecture|SNA]], and two networking file systems: [[Network File System (protocol)|NFS]], licensed from [[Sun Microsystems]], and IBM [[Distributed Services]] (DS). DS had the distinction of being built on top of SNA, and thereby being fully compatible with DS on the IBM midrange [[AS/400]] and mainframe systems. For the graphical user interfaces, AIX v2 came with the X10R3 and later the X10R4 and X11 releases of the [[X Window System]] from [[MIT]], together with the [[Xaw|Athena widget set]]. [[Compiler]]s for [[C programming language|C]] and [[Fortran]] [[programming language]]s were available.

Some RT PCs were also shipped with the Academic Operating System (AOS), an IBM port of [[Berkeley Software Distribution|4.3BSD]] Unix to the RT PC. It was offered as an alternative to [[IBM AIX|AIX]], the usual RT PC [[operating system]], to US universities eligible for an IBM educational discount. AOS added a few extra features to 4.3BSD, notably [[Network File System (protocol)|NFS]], and an almost [[ANSI C]]-compliant [[C (programming language)|C]] [[compiler]]. A later version of AOS existed that was derived from 4.3BSD-Reno, but it was not widely distributed.

The RT forced an important stepping-stone in the development of the X Window System, when a group at [[Brown University]] ported X version 9 to the system.  Problems with reading unaligned data on the RT forced an incompatible protocol change, leading to version 10 in late 1985.