Various flavors of UNIX
* AIX--major--IBM's version that runs on the RS/6000 series of RISC systems and mainframes. Over 500,000 RS/6000 systems have been sold!
* BSD--minor--This version has a lesser presence in the marketplace. Although many variants can trace their heritage to BSD, it is not that popular as a product.
* HP-UX--major--Hewlett Packard's (HP) version with a strong hardware presence in the marketplace and a strong future growth path.
* IRIX--minor--While the Silicon Graphics (SGI) machines are wonderful for graphics, they have not found wide acceptance in business environments.
* Linux--minor--Although this is a very nice and free variant, it has little commercial presence in the marketplace (probably because corporations do not want to run their mission-critical applications without a vendor they can sue when there is a problem). See the SAMS Linux Unleashed series books (Red Hat and Slackware) for detailed information.
* Solaris--major--Sun Microsystems' version with a strong hardware presence in the marketplace and a strong future growth path.
* SunOs--minor--Largely being superseded by Solaris installations. A good variant, but it is difficult for a company to support two versions of UNIX at a time.
* SVR4--major--This version has a strong presence in the marketplace. In addition, many variants can trace their heritage to System V Release 4.
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The most commonly used UNIX variants, including:
* HP-UX (Hewlett Packard)
* Solaris (SunSoft)
* SVR4 (AT&T)
* AIX (IBM)
* BSD (Berkeley Software)
* Linux
* SunOS (predecessor to Solaris)
* IRIX