In the course of upgrading my desktop system, I decided to go with a system board and processor suitable for running 64-bit Windows as well as one that could support enough memory for me to use either Microsoft Virtual PC 2004 or VMware's VMware Workstation 5.0 to run additional OSs in their own memory space. I ended up specifying an Intel 925 chipset-based motherboard with an EMT processor. This was prior to the release of the dual-core chips, or I might have gone that direction. I thought that with a fast 64-bit Pentium 4 processor, the latest PCI Express video adapter, and 4GB of RAM I'd be set for a year or so in term of technology on hand.
The system arrives, configured and burned in, but with no OS, per my specifications. I install Windows XP Professional Service Pack 2 (SP2) and the various applications I use, attach additional storage, and configure the dual-monitor setup to my liking. Most of my applications limit the amount of memory they use (e.g., Adobe Photoshop CS2 reports that 2GB of memory are available to it even when additional memory is available), but I thought with 4GB of RAM, I'd be able to run multiple memory-intensive applications simultaneously.
While getting ready to set up Virtual PC, I noticed in the Task Manager Performance tab that the OS is reporting well under 3GB of physical memory. Somewhat concerned, I reboot the system and open the BIOS configuration to check the memory configuration. The BIOS and power-on self test (POST) report that 4GB of memory is installed and functioning, but during the POST, which is usually hidden from view, I catch a message that states that system resources are using 1126MB of memory.
I didn't know which system resources on the motherboard could be using more than 1GB of memory, so I searched the Intel support site and discovered that a BIOS update for my new motherboard is available. Thinking I might have found the problem, I update the BIOS and reboot; I now have 864MB of system memory being used by system resources.
Although I've recovered 300MB of useable memory, I'm still concerned about the large amount of memory being reserved. A phone call to Intel technical support resolves the problem. What I've run into is primarily an artifact of my decision to use a high-end PCI Express video adapter. PCI Express severely cuts into the addressable memory on the motherboard. The PCI Express configuration space reserves 256MB of addressable memory, whereas another 512MB is reserved for use by the PCI Express ports and a few other video-related features. An additional 70MB or so at the top of the memory address range is reserved for the BIOS and various system devices.
So what I have, despite my investment in a computer with 4GB of physical memory, is one with a little more than 3GB and a system that is far less capable than I thought it would be for the business use I had envisioned for it. The motherboard can't accept any more memory, so even with a 64-bit OS, I would still have only 3GB available.
Although the new computer system remains more than acceptable for my daily use, I'm going to look at more capable motherboards and AMD processor-based systems to see what I can put together as the best computer for my particular needs and one that can make available the memory footprint I desire.