ISC's 1977 offering, IS/1, was a Version 6 Unix variant enhanced for office automation running on the PDP-11. IS/3 and IS/5 were enhanced versions of Unix System III and System V for PDP-11 and VAX. ISC Unix ports to the IBM PC included a variant of System III, developed under contract to IBM, known as PC/IX, with later versions branded 386/ix and finally INTERACTIVE UNIX System V/386. ISC was AT&T's "Principal Publisher" for System V.4 on the Intel platform. ISC was also involved in the development of VM/IX and enhancements to IX/370. They also developed the AIX 1.0 for the IBM RT PC, again under contract to IBM, although IBM awarded the development contract for AIX version 2 of AIX/386 and AIX/370 to the competing Locus Computing Corporation.
PC/IX
Although observers in the early 1980s expected that IBM would choose Microsoft Xenix or a version from AT&T Corporation as the Unix for its microcomputer, PC/IX was the first Unix implementation for the IBM PC XT available directly from IBM. According to Bob Blake, the PC/IX product manager for IBM, their "primary objective was to make a credible Unix system - not try to 'IBM-ize' the product. PC-IX is System III Unix." PC/IX was not however the first Unix port to the XT. Venix/86 preceded PC/IX by about a year, although it was based on the older Version 7 Unix. The main addition to PC/IX was the INed screen editor from ISC. INed offered multiple windows and context-sensitive help, paragraph justification and margin changes, although it was not a fully fledged word processor. PC/IX omitted the System III FORTRAN compiler, the tarfile archiver and did not add BSD tools like vi or the C shell. One reason for not porting these was that in PC/IX individual applications were limited to a single segment of 64 KB of RAM. To achieve good filesystem performance, PC/IX directly addressed the XT hard-drive rather than doing this through the BIOS, which gave it a significant speed advantage compared to MS-DOS. Because of the lack of true memory protection in the 8088 chips, IBM only sold single-user licenses for PC/IX. The PC/IX distribution came on 19 floppy disks and was accompanied by a 1,800-page manual. Installed, PC/IX took approximately 4.5 MB of disk space. An editorial by Bill Machrone in PC Magazine at the time of PC/IX's launch flagged the $900 price as a show stopper given its lack of compatibility with MS-DOS applications. PC/IX was not a commercial success although BYTE in August 1984 described it as "a complete, usable single-user implementation that does what can be done with the 8088", noting that PC/IX on the PC outperformed Venix on the PDP-11/23.
INTERACTIVE UNIX System
PC/IX was succeeded by 386/ix in 1985, a System VR3 derivative. Later versions were termed INTERACTIVE UNIX System V/386 and based on System V 3.2, though with elements of BSD added. Its SVR3.2 kernel meant diminished compatibility with other Unix ports in the early nineties, but the INTERACTIVE UNIX System was praised by a PC Magazine reviewer for its stability. After its acquisition of Interactive, Sun Microsystems continued to maintain INTERACTIVE UNIX System, offering it as a low-end alternative to its System V.4-based Solaris, even when the latter had been ported to x86-based desktop machines. The last version was "System V/386 Release 3.2 Version 4.1.1", released in July 1998. Official support ended on July 23, 2006, five years after Sun withdrew the product from sale. Until version ISA 3.0.1, INTERACTIVE UNIX System supported only 16 MB of RAM. In the next versions, it supported 256MB RAM and PCI bus. EISA versions always supported 256MB RAM.
