Research finds that running 10-50 apps on a mainframe costs less than on one Linux or Solaris server.
I was lucky enough to work on IBM AS/400 system for some time. We used to run AIX, RedHat Debian Linux natively on an iSeries Logical Partition (LPAR).
Research house Illuminata's report, 'IBM System z TCO: Man Bites Dog' shows that running 10-50 applications on a mainframe costs less than running the same workload on a one server/one application basis where the servers run Linux or Solaris.
Reasons for low cost / TCO
=> Mainframe has better cooling technology - A mainframe typically requires less electricity and air conditioning than many 1U servers running the same workload.
=> Cost of people - When running multiple applications the mainframe's people costs are much less than those needed to run the same workload on distributed systems.
=> Mainframe memory prices have fallen significantly in recent years.
This is an interesting study :)