System Requirements

• Microsoft Windows 95/98/ME/NT/2000/XP/Vista
  (see below for information about Mplus on Mac OS X)
• At least 8 MB of RAM
• At least 20 MB of hard disk space

Mplus Version 5 is available for 32-bit and 64-bit operating systems.

Memory requirements for Mplus (both RAM and virtual memory) depend on the type of analysis and the amount of data. For example, analyses using numerical integration with large samples can be computationally heavy and may require a large amount of memory.

Mplus 32-bit on 32-bit Windows: The Windows 32-bit operating system limits all applications to a maximum of 2GB of total memory (RAM and virtual memory).

Starting with Mplus Version 4.21, Mplus is capable of using an additional 1 GB of total memory, for a maximum of 3 GB, on some Windows 32-bit operating systems. For Mplus to use the additional memory, the /3GB switch must be specified in Boot.ini. This switch allows applications like Mplus, that are "large address aware", to use 1 GB of additional total memory above 2 GB.

Note that changes to the Boot.ini may have undesirable effects. Caution should be taken when making any changes. Muthen & Muthen is not responsible for any problems that may arise if such changes are attempted and does not provide support for any problems related to these changes.

Mplus 32-bit on 64-bit Windows: The Windows 64-bit operating system limits all 32-bit applications to a maximum of 2GB (or 4GB for applications like Mplus that are "large address aware") of total memory (RAM and virtual memory). Note that the /3GB switch is not applicable to Windows 64-bit operating systems.

Mplus 64-bit on 64-bit Windows: The Windows 64-bit operating system limits all 64-bit applications to a maximum of 8 terabytes (8000GB) of total memory (RAM and virtual memory).

Mplus on Mac OS X: While Mplus is intended for Microsoft Windows, some users have reported success installing Mplus on Intel-powered Mac using either Parallels Desktop or VMware Fusion software. Mplus support will not be provided for the installation and use of these software or the installation of Mplus using these software.

The PATH Environment Variable

The Run Mplus option in the Mplus Editor requires that the Mplus installation directory be listed in the PATH environment variable. The PATH environment variable must also be set at the system level for Mplus to work properly in a multiple user environment. The Mplus installation process will try to set the PATH environment variable at the system level.

If this attempt fails, problems may arise when using the Run Mplus option in the Mplus Editor or when trying to update Mplus. Users will be alerted that Mplus is unable to start when running Mplus or Mplus is not found when updating Mplus.

To fix this problem, the PATH environment variable can be set manually. The instructions given below are for Windows 95/98/ME/NT/2000/XP operating systems. Similar instructions can be used on Windows Vista.

1. Log on with an administrator account.
2. Right-click on My Computer and select Properties.
3. Go to the Advanced tab and click on the Environment Variables button.
4. The system level variables are located in the bottom section. Locate the Path variable and click on Edit.
5. Add the Mplus installation directory (default is C:\Program Files\Mplus) to the end of the Value field, separated from the other directories by a semicolon.
6. Click OK to exit.

Mplus Temporary Files

Mplus uses intermediate files for controlling outputs. These files are created in the working directory. The working directory is usually the directory with the input file. There is one instance when it is not and that is when Mplus is first opened and the recent file list is used to open a previous input file. To ensure that the working directory is always the directory with the input file, always use the File -> Open/Save options for opening/saving an input file.

There is one other temporary file that is created by Mplus but not stored in the working directory. This file does not contain any specific results from the current run. The only information written to the file is the name of the output file. Mplus stores this file in the directory specified by the TEMP environment variable -- a setting on most computers with the Windows operating system. There is no specific setting in Mplus to change the location of this directory. To change the location where Mplus stores this file, the TEMP environment variable must be changed. This will affect other programs that use the TEMP environment variable.