Extending Memory Address Space (Enabling the \3GB Switch)
Inventor has a feature in R6 SP2 and later, that will enable the user
to access a larger virtual memory space than normal. Typically,
Microsoft Windows reserves the upper half of the 4 GB virtual address
space of any process for the operating system, and leaves the remaining
2 GB for the application process, including the space for the code
pages, the stack, and all dynamically allocated memory. The 3GB feature
divides the memory space differently, providing 3 GB for the
application and 1 GB for the operating system. This option was provided
in response to requests from customers who commonly work on extremely
large assemblies that consume the full 2 GB of virtual memory space and
still need more memory. The feature has been tested using some of those
very large models.
In order to enable the feature, you must change your boot.ini file
(which is typically located at C:\boot.ini) to have the /3GB option, as
shown below. We recommend that you copy the original line, modify the
copied line to add the option and the identifying string. This will
enable you to choose at boot time whether to use the option or not.
(The default will be to use whichever line is first). The copied line
is highlighted below in blue, with the modified portions of the line
shown in red.
***WARNING***
Problems caused by improperly editing the BOOT.INI may prevent your
system from booting correctly and could render your computer operating
system unusable. Microsoft has provided a wealth of critical
information you need to know about the BOOT.INI file in the Microsoft
Knowledge Base at
http://support.Microsoft.com/support.
Edit the BOOT.INI file only at your own risk and only after backing up
the original.
Example BOOT.INI file:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP
Professional" /fastdetect
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft
Windows XP Professional 3GB"
color="#ff6600">/3GB /fastdetect
You should ensure that you have a total of at least 3GB set
aside for the Paging File Size to fully utilize the available address
space. Also note that every concurrently running application is sharing
the available paging file size, so setting to something more than 3 GB
(such as 4 GB) is recommended. In order to check the amount of memory
you currently have allocated follow these steps:
1) Press the Windows+Pause|Break keys simultaneously to gain access to
the System Properties
2) Click the Advanced tab, then, Settings button in the Performance
group.
3) In the Performance Options dialog box click the Advanced tab and
look at the section titled Virtual Memory. The total amount of memory
currently allocated will be displayed here in megabytes
To ensure that Inventor is actually allocating memory in the 3 GB
range, start Inventor and then choose Help>About Autodesk Inventor.
The first line of text under the splash screen image should say:
Autodesk Inventor %release% - 3GB. If the - 3GB is shown, Inventor is
successfully using the feature; otherwise, it is not. (Releases prior
to Inventor 6 SP2 have not been enabled. Of course, the release number
may vary.)
Limitations:
Executable files must be specially built to enable the larger address
space. The only Autodesk executable file shipped in the Autodesk
Inventor Series to be enabled to leverage the 3GB switch is
Inventor.exe. Other executables shipped with Autodesk Inventor have not
been enabled. Most likely, the applications provided by other software
vendors have also not been enabled to use this feature.
The feature only works on Windows XP. Furthermore, the Windows XP SP1
service pack had disabled it. To re-enable it for Windows XP SP1, there
is a hotfix from Microsoft that must be applied.
(q328269_WXP_SP2_x86_ENU.exe). This seem to be fine in SP2.
It is not possible to enable the feature on Windows NT, Windows
2000, or Windows 9x.
Be aware that the OS now has less memory space. It is not completely
clear what implications that may have on Windows XP, but it would be
wise to be somewhat cautious with regard to the total application load
placed on Windows while running in this mode. If you don’t specifically
need the larger address space, it is recommended that you do not enable
this option.
Only marginal performance improvement could occur on systems using swap
space on the systems hard disk to increase the available virtual memory
rather than using physical memory (1 gigabyte of physical memory and a
3 gigabytes swap file). A significant amount of time reading and
writing occurs when the system hard disk is used reducing the benefit
of this feature.
(Thanks to Richard for this well written summary!)
-Kevin
![Autodesk Design & Make Report](https://forums.autodesk.com/t5/image/serverpage/image-id/1350519iCB55845EBFC43016/image-size/large?v=v2&px=999" "Autodesk Design & Make Report")