Linux on the IBM S/390

About System 390

The System 390, or S/390, comprises a broad family of mainframe computer models based on the 32-bit IBM 390 processor architecture formally defined in the 390 Principles of Operation manual (POP for short).

The 390 architecture is the lineal descendant of the 1960s IBM 360 and the 1970s IBM 370 processors. IBM 390 CPUs commonly run at 750 MHz. Forthcoming are both much faster CPUs and a 64-bit architecture.

A copiously illustrated view of the state of S/390 silicon is the recent IBM Research Journal issue "IBM S/390 Server G5/G6".

Multiprocessor machines commonly range from two to twelve CPUs. Processor and other S/390 hardware resources can be virtualized and partitioned between multiple operating system images in the "hypervisor", which runs at either the microcode level (Logical Partition or "LPAR") or at the operating system level (VM/ESA) [See sidebar, "About VM".]

Mainframes are much more than their central processing unit, being specialized for high rates of I/O transfer. Channel architecture offloads I/O operations onto discrete channel controllers which execute programs written into shared memory from the CPU, making byte data transfers inefficient but block transfers, especially large block transfers, more efficient than with the sorts of I/O architectures common in the PC and Unix world.

Mainframes are also valued for their reliability, as Byte pointed out in a 1998 article, "Why Mainframes Rarely Crash."

S/390 mainframes run a variety of operating systems either natively, in an LPAR, or under VM. These operating systems include VM/ESA, OS/390, DOS/VSE, TPF, and now Linux.

Qualified application developers (see the S/390 PartnerWorld for Developers web page) can obtain S/390 hardware at a discount, and the VM operating system without monthly licensing. IBM sales philosophy being very much based on one-on-one relationships with individual customers and developers, general price information is as hard to come by as free advice from a lawyer; however, it appears that the entrée for an up-to-date developer model is around $15,000, substantially more than a Unix workstation but also substantially less than $500,000 to $2,000,000 a commercial user might easily spend for a production S/390 model.

Alternatives to owning your own IBM S/390 include the following:

• Emulation on Intel, available from Fundamental Software Inc.,
• A local university, many of which can provide accounts on an S/390,
• Contract programming at IBM, which will often bring the contractor into formal or informal contact with the S/390