Magnify Your Image

By Neil Armstrong, Senior Programmer, Robelle

With the release of MPE/iX 6.5 Express 2, a new version of Image is available with new expanded capacities. Back on December 8th, in the 1st part of this article, we reported that this new version of Image now supports, 1200 Items, 240 datasets and 64 paths for a Master.

A second and more significant change to Image is also included in the C.09.02 release and that is a change from entryname format to entrynumber format. Sounds obscure and uninteresting, but is actually quite exciting.

Previously, Image internal record numbers consisted of 32-bits containing a block number and a record number within that block. The first 24 bits would contain the block number and the last eight bits would contain the position of the record within that block.

Because the maximum size of a block was limited to 5120 bytes and the total number of blocks was limited to what would fit in 24 bits (2**24-1), this meant that the total number of bytes was approxiametely 80Gb. Or to be precise, the total bytes that can be stored per dataset is:

Result=85899340800.0  Computed using Qedit's calculator

Now with this new version of Image available in MPE/iX 6.5 Express 2, the pointers are in entrynumber format, which is no longer block based, but rather the record number of the entry.

This means that the limiting size of the dataset is no longer based on block numbers and total space, but rather is limited to the total record numbers which can be tracked in the 32-bits (less the sign bit): 2**31-1, which totals just over 2 billion records:


With the new limit being 2 billion records and the entry size maximum being 2378 halfwords or 4756 bytes the new limit is now, well really, really big, in fact over 10 Terrabytes.

Considering that the largest dataset I've seen is 72 Gb, I think this will meet the needs of most HP 3000 installations for quite some time to come.

This new version of Image is supported in the Suprtool pre-release 4.3.03 which is due to be available on December 28, 2000. HowMessy currently will print an error message when trying to report on databases with the entrynumber format as many of the block based calculation will not make sense for these types of databases.
December 28, 2000