IBM no longer provides Perl for its mainframe machines, see Software withdrawal: Selected IBM System z platform products (a copy is here: IBM-Withdrawal-ENUS913-252. It looks like they have not heard that Perl is the duct tape that holds the internet together. Similarly IBM withdraw PHP from their mainframe platform. So Wikipedia and Facebook will not run on big iron. Not that Wikipedia or Facebook ever wanted to, but now IBM pulled the plug.
In the same vein all IBM has to offer their customers is 32-bit COBOL on their mainframe, so customers can only use less than 2 GB, see Memory Limitations with IBM Enterprise COBOL Compiler.
In earlier times IBM tried to sell their VisualAge products, which where notoriously slow, and never really took off. Now they aggressively sell WebSphere.
Who makes these decisions? And who approves this?
In defense of IBM, there is a company called Rocket Software which provides Perl and PHP. So it’s like going to McDonald’s ordering a hamburger, but the clerk tells you that you should buy the bread separately from the nearby bakery.
Recently I learned the hard way that IBM Enterprise COBOL compiler cannot generate 8-byte long POINTER variables, but only 4-byte pointers, meaning, that you cannot use more than 2GB in COBOL on a mainframe. I.e., you cannot make use of AMODE=64 with COBOL on the mainframe. You can run in AMODE=64, but you cannot exploit it. BTW, we have the year 2013. So, no big-data on mainframe with COBOL.
IBM Assembler and C/C++ can fully exploit AMODE=64, i.e., can use 8-byte long pointers.
Mainframe rehosting is about replacing the whole mainframe with one or multiple Linux boxes, or at times, move portions of the application landscape from the mainframe to Linux. Thereby you basically keep many of the hitherto used development- and runtime-environment, like COBOL, DB2, IMS, CICS, etc. The goal in mainframe rehosting is to dramatically reduce costs. If you are dauntless you can also move to Windows.
The point is that you do not rewrite your applications but rather just move your applications, i.e., you recompile your applications on new hardware. So all accumulated experiences with the software is fully preserved.
In 2008 I started writing a paper on mainframe rehosting, see Mainframe Rehosting.
During 2008-2011 the paper has been revised somewhat. The paper is in German.