Memory, RAM, and Address Space

LTspice was the first PC-based SPICE program to implement its own 64bit address on the hard disk to allow one to view waveform data files of essentially unlimited file size. LTspice can address data files containing many Gigabytes of data and page in up to four Gigabytes at a time for plotting in the waveform viewer.

However, most editions Microsoft Windows allow a maximum of 2GB of address space for application software despite the fact that 32 bits can address 4GB uniquely. If, as is common, you have 4GB of physical RAM, you can configure Windows to override this default. Under Windows XP and variations, you can edit the boot.ini file to add the "/3GB" option to the operating system line. From http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx:

Typical boot.ini file:

[boot loader]

timeout=30

default=multi(0)disk(0)rdisk(0)partition(2)\WINNT

[operating systems]

multi(0)disk(0)rdisk(0)partition(2)\WINNT="????" /3GB

Where "????" would be the programmatic name for one of the following:

Windows XP Professional

Windows Server 2003

Windows Server 2003, Enterprise Edition

Windows Server 2003, Datacenter Edition

Windows 2000 Advanced Server

Windows 2000 Datacenter Server

Windows NT Server 4.0, Enterprise Edition

Microsoft Vista is different and you should use the utility bcdedit.exe, e.g.:

C:\Windows\System32>bcdedit.exe /set IncreaseUserVa 3072

The change doesn't take place until the system reboots.