IBM's new system uses IBM's specialty Linux processor and runs either Novell SUSE or Red Hat systems. They are not using mainframe operating system z/OS but includes mainframe management software as well as IBM's z/Virtual Machine system on that machine. So IBM Machines are going to rock with Linux...
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http://www.computerworld.com/s/article/9142007/IBM_s_newest_mainframe_is_all_Linux_