Increased Number of DSTs

Introduction

DSTs are Data Segments used in MPE/iX for supporting Compatibility Mode (CM) operation. With the increase in capabilities of HP 3000 systems and MPE/iX OS over the years, it became necessary to increase the total number of DSTs supported in MPE/iX. This article gives a technical overview of the changes done in MPE/iX Release 6.5 to increase the number of available DSTs from 16383 to 65535. It also describes the benefits that this change can bring to HP 3000 customers.

Technical Overview

Earlier versions of MPE/iX supported a total of 16383 DSTs. This limit of 16383 DSTs was mainly due to limitations in some internal data structures of the OS that were used to handle DST numbers. These limitations have been adequately addressed in MPE/iX 6.5 to allow handling of larger DST numbers. This has helped in increasing the total number of DSTs from 16383 to 65535.

Prior to MPE/iX 6.5, we had a total of 16383 DSTs which were shared by both OS as well as user applications. With the 6.5 release, we distinguish between DSTs used by the OS and DSTs allocated by user application programs. We now have about 16383 DSTs exclusively available for user applications. The OS has a separate pool of 49152 DSTs for its own internal usage. These two together make a total of 65535 DSTs available in the system.The increase allows more DSTs to be available to satisfy the requirements of the OS as well as user applications.

Benefits to Customers

The increase in number of DSTs brings many advantages for MPE/iX customers. Since DSTs are mainly used inside the OS to manage jobs and sessions, an increase in the number of DSTs available implies that the system can now run more jobs and sessions compared to earlier releases. The increase in number of jobs/sessions can, in turn, help in increasing the number of simultaneous users supported on the system.

With 16383 DSTs now exclusively available for user applications, users can run more CM applications that make use of DSTs at application level.

Since MPE/iX Networking modules are also major consumers of DSTs, the increase in DSTs facilitates capacity improvement in Networking modules. For example, the DST increase has contributed largely to the increased number of Virtual Terminal (VT) connections available from MPE/iX 6.5 onwards.

Conclusion

In summary, the increase in number of DSTs on MPE/iX 6.5 brings many advantages to HP 3000 customers and paves the way for future capacity expansions in many more areas of MPE/iX. The increase to 65535 DSTs is expected to meet the requirements for years to come and carry MPE/iX forward through its future enhancements.