This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.
You really should be upgrading. Even if you can find what you need (usually it's TCP/IP that folks are looking for), it's going to be very expensive- if you find it at all..
These folks MAY be able to help you: Blue Chip Computer Systems: https://www.bccs.com 310-410-0126.
Try Ebay also, though I haven't seen much there recently.
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