The latest market share server numbers from IDC, released Wednesday, show that users have put off purchasing new Unix systems in recent months, cutting its share of overall server spending to one of the lowest levels ever.

The IDC report, released Wednesday, shows worldwide Unix revenues of $2.3 billion, or just over 22% of total spending on servers, during the first 2010 quarter. The Unix server share of server revenue is down 10.5 percentage points from the year ago quarter.

Unix servers are mid-to-high end system traditionally used to run mission critical systems, but their use has been gradually eroding as the capabilities of x86 servers increase. The Unix servers run several Unix variants, including Solaris, AIX and HP-UX.

The shift from such Unix variants is perhaps most dramatic in the supercomputing business.

The Top500 supercomputer list offers detailed statistics on processors, architecture and operating systems deployed in these systems. Late last year, Linux was the operating system of choice for just over 78% of the Top500 supercomputers, and even a bit higher when Red Hat and Suse-specific implementations are added. The highest ranked Unix system was IBM's AIX at 4.4%.