gtpc3m1w | Concepts and Structures |
In addition to software system features designed to achieve the performance objective, the TPF system also takes advantage of hardware facilities to meet this end. The module record cache is a hardware facility that is an integral part of a module control unit (CU) (also called a module controller). Note that not all module controllers used in a TPF system are equipped with this facility.
Based upon a user installation's requirements, the TPF system can be configured with:
Module record caching is similar to VFA caching with regard to:
However, there is an important difference: data records that reside in the module cache allow multiple CPCs in a loosely coupled complex to share a single copy of the data, whereas, data records that reside in VFA cache are usually processor (CPC) unique data records.
Records that are not defined as module record cache candidates are written directly to the module surface, and the use of the module record cache is not called. Records that are defined as module record cache candidates are first written to the cache before ultimately being written to the module surface.
There are two general categories of module record caching: fast write and retentive write. The main difference between fast write and retentive write is the point at which the TPF system is notified that the I/O command is complete.