System virtual memory is used to satisfy additional memory requirements.21.2. How the Program Uses Work Space
To understand how the program uses its work space (the shaded portion in Figure 21.1: Comparing
Available Memory (p. 327)), you need to understand its two components:database space and scratch
space, as shown in Figure 21.2:Work Space (p. 328). Database space is used to work with the program
database (model geometry, material properties, loads, etc.). Scrat ch space is where all internal calculations
are done - element matrix formulation, equation solution, Boolean calculations, and so on. (Note that
part of the scrat ch space stores binary file buffers; see the description of NUM_BUFR later in this chapter.)
The default work space for 64-bit machines is 1 GB (1024 MB), of which 512 MB are assigned to database
space, and 512 MB are assigned to scrat ch space. For 32-bit machines, the default work space is 512
MB, of which 256 MB are assigned to database space, and 256 MB are assigned to scrat ch space. These
sizes represent the amount of memory that is allocated upon program startup for the database and
scratch spaces.
Figure 21.2: Work Space
If your model database is too big to fit in the initial database space, the program will, by default, attempt
to allocate additional memory to hold it (64-bit systems only). If it cannot, the program uses ANSYS vir-
tual memory, which is a file written by the program that is used for data overflow. The main difference
between system virtual memory and ANSYS virtual memory is that the former uses system functions to
swap data between memory and disk, whereas the latter uses Mechanical APDL programming instructions.
The file used for ANSYS virtual memory is called the page file and has the name Jobname.PAGE. Its
size depends entirely on the size of the database. When the page file is first written, the program issues
a message to that effect. Use of the page file is not desirable because it is a less efficient way of pro-
cessing data. You may be able to prevent it by allocating more database space (discussed in How and
When to Perform Memory Management (p. 329)).
If internal calculations can't fit in the initial scrat ch space, the program will, by default, attempt to allocate
additional memory to meet these requirements. If this occurs, you will see an alert message informing
you that the problem has grown beyond the specified initial memory allocation and that the program
has allocated additional memory.
In general, you should have enough physical memory to comfortably run an analysis job. If you are
using virtual memory only temporarily or using a relatively small amount of virtual memory, the per-
formance impact will typically be small. However, using a significant amount of virtual memory, partic-
ularly during solution, can degrade performance as much as a factor of ten.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationMemory Management and Configuration