infact to quote : "Windows NT-based operating systems are working in so-called protected mode, meaning that the operating system is running at the highest �current privilege level� (CPL=0) whereas user applications are running at a low privilege level (CPL=3) that will not grant direct access to either memory space used by the kernel or else I/O ports to applications. The easiest way of protecting the memory space allocated to the operating system from unauthorized access by any user application is to split the 32-bit memory space into two separate, arbitrarily defined 31-bit memory spaces ranging from �2^31 to +2^31. In this case, all memory addresses allocated to the operating system will be lower than 0 whereas all user applications will only have access to the positive memory range. Attempts by applications to access the negative virtual address space will result in a fault handler execution that can create for example an error message saying �Insufficient Memory� or �Out of Memory� depending on the personal taste of the programmer. As a consequence, all user applications together can only access a total of 2 GB of combined physical and virtual memory (with virtual memory in this case referring to HDD space allocated to the page-file). These limitations apply to WindowsNT, WindowsXP and Windows Server2003 (Windows.net). One exception is Windows 2000 Server Enterprise Edition along with some configurations of Microsoft Exchange Server 2000 and Microsoft Windows 2000 Advanced Server that allow the so-called 3GB switch to enable 3 GB of usable memory for applications. Bottom line is that WindowsXP cuts the memory accessible by 32-bit applications and processors in half meaning that of the 4 GB total memory available in a 32-bit address space only 2 GB are usable by any application. If more memory is required, the user either needs to migrate to a 64-bit processor and operating system or else to the old-fashioned Windows2000 Server. The latter will work up to a total of 3 GB of memory needs for applications. If more memory is required, the only way out is a 64-bit edition of WindowsXP or 2003 Server along with the necessary hardware to support it." I would guess it comes down to this : "Attempts by applications to access the negative virtual address space will result in a fault handler execution that can create for example an error message saying �Insufficient Memory� or �Out of Memory� depending on the personal taste of the programmer." - and it's fouling the scene. thing is, it is only in the last YEAR that systems at home have been getting to this limit. remember when Poser 4 / Propack had to be updated to handle 1gb + ram? and the recommendation was to cap your virtual at 2gb?