NASTRAN-95 vs MYSTRAN

[borges]

You buy a 4g ram PC, you can load some models. When you want to load bigger model, maybe you need to open the PC to expand the ram to 8g. 
It is the same as the OCMEM. You need to edit the program to increase it. 

It doesn't matter how many RAM your PC has. Mine has about 16 GB.

However, none of that matters: OCMEM is an environment variable that you pass to the NASTRAN-95 executable to tell it how many (four-byte) words it should attempt to allocate for its open core. You can set it to any positive integer value equal to or less than 14000000, representing 56 MB of open core. Setting it to any value outside of that set (e.g. "14000001", "-5", "2.71828", "donuts"), regardless of file validity or model scale, will cause a fatal message to be issued:

Code:

  LARGEST VALUE FOR OPEN CORE ALLOWED IS:    14000000
  ERRTRC CALLED
  NAME=WRTMSG 
  IVAL=         100




                                        * * * END OF JOB * * *
1
JOB TITLE =                                                                     
DATE:  0/ 0/ 0
END TIME: 21:35:48
TOTAL WALL CLOCK TIME      0 SEC.

That's the entirety of an .f06 file I just produced by calling NASTRAN-95 with a good model while having set OCMEM=14000001.

No matter how much memory your PC has, NASTRAN-95 will never allocate more than 56 MB for its open core, thus creating an upper bound on loadable model size.

Furthermore, even if you changed the code to let NASTRAN-95 use all of its open core address space (like IBM did), you'd still be limited by the fact it most likely uses 32-bit integers to address the open core, so even then you'd be limited to around 2 (or 4 if unsigned) GB, which is nice, but way below large production-scale models in use with modern NASTRANs such as Simcenter's.