By Timothy Prickett Morgan
IBM Corp is reportedly telling its low-end mainframe customers that are members of the World Alliance of VM and VSE (WAVV) user group that it plans to offer support for Linux on the S/390 hardware by the middle of next year. It says it will wrap the VM operating system around it, allowing Linux to run as a guest operating system on the hardware. This is the same approach IBM originally used to support its first Unix variant, AIX/370, on mainframes back in the 1980s. Since that time, IBM has launched a true Unix server line running AIX, the RS/6000s, and added Unix APIs to its OS/390 operating system to the extent that OS/390 qualifies as a variant of Unix.
Odds are, IBM is trying to take the cheap way out by using VM to host Linux rather than porting Linux straight to its S/390 Multiprise 3000 and 9672 mainframes. Whether or not it goes all the way and offers Linux natively on S/390 iron or adds Linux APIs and ABIs to OS/390 so it is effectively offering full Linux support remains to be seen.
From a practical standpoint, running Linux as a guest under VM is the cheapest and easiest way to get Linux working on IBM’s mainframe hardware. VM partitions have been used to support VSE, MVS, AIX and other obscure operating systems for years and IBM is well acquainted with how to make it work well. Many of the big banks and financial institutions in the world still run VM rather then MVS or OS/390 because VM predates both of these – it was developed in a skunkworks behind MIT by IBM in the 1960s and remains IBM’s smartest piece of work – and is still better suited for their giant batch applications because it is a more streamlined operating system than either MVS or OS/390.
The fact that IBM is porting Linux to VM does not mean that it will not do the same for OS/390. OS/390 can also have logical partitions that could support Linux provided that mainframe channel drivers could be interfaced with the Linux kernel. In either case, by putting Linux in a VM or OS/390 partition IBM would allow its mainframe customers to run Apache, Sendmail and other popular internet applications without having to actually port the applications to the VM and OS/390 compilers. A full native port of Linux is possible of course, given the fact that the S/390 iron is effectively 32-bit system, just like Linux is. With all this excess Y2K capacity sitting around (and causing S/390 sales to implode), Linux within VM and OS/390 partitions will at least give mainframe shops something to do with all those extra MIPS. As VM and OS/390 get converted to 64-bit operating systems over the next two years to run on the 64-bit Freeway S/390 mainframes due in 2000, a 32-bit operating system like Linux will still be able to run on the iron.
