Architecture Management for Ensuring Software Compatibility in the VAX Family of Computers

The cost of computer system software can easily exceed the cost of the hardware that executes it. For the large-system user, the software investment is often shared by multiple installations of identical hardware. Eventually, though, users tend to buy new hardware-a fact attributable to several reasons. New technology permits higher performance at lower cost. Some installations may not require the performance level of the original hardware, and others may require higher performance. Thus different hardware implementations of the same architecture will be needed. So, with varying hardware implementations in a family of computers, software compatibility becomes a major requirement. Software compatibility preserves the software investment for the computer vendor as well as the user. It allows computers with different cost, performance, and technological characteristics to be used interchangeably to run the same software.