Linux on the Mainframe

Around 1960, there were many computer systems in the marketplace, each developed for a specific purpose. Some were optimized, for example, to do accounting, others to solve engineering problems or to help scientists with complex calculations. At the time, about 80% of the total customer cost of the IT environment was spent on hardware. Therefore, fully exploiting the capabilities of a piece of hardware was crucial for an efficient IT operation.

To efficiently use IT resources, it was sometimes desirable to move a program between computers. This was not easy. Figure 2-2 illustrates the relationship between the hardware, or electronic layer, and the program, application, or user layer at that time. To move between different computers, it was necessary to rewrite programs, because the interface to the programs was different for each machine.

In response this problem, Gene Amdahl, Fred Brooks, and Gerry Blaauw envisioned and implemented the IBM System/360 (S/360)^[3] architecture. The five-member S/360 family of computers was announced in 1964.

^[3] The "360" in the name stands for the 360 degrees of a full circle (not for the 1960s when it was invented).

The basis for S/360 was the idea that computing could be abstracted so that a very broad range of problems could be solved within the confines of a single computer architecture. In fact, we can say that all computing can be reduced to the following operations:

1. Get some data.

2. Perform some computation (or manipulation) on that data.

3. Save the data that resulted from the computation.

The IBM team distinguished between architecture, which is the theoretical behavior of the system, and design, which is an implementation of the architecture. They designed machines that implemented the general architecture in a way that allowed subsets of the problem space to be solved better (faster or more cost-effectively) on one model compared to another model. For example, some models of the S/360 family, such as the model 95, were considered to be supercomputers. The model 65 was the workhorse, top-of-the-line business computer, and the model 25 was for small businesses. All three used the same architecture across a wide range of applications.