Guest Paul Randall Posted July 29, 2007 Posted July 29, 2007 Re: Does Windows XP Pro have a 3GB limit on RAM ? "ship" <shiphen@gmail.com> wrote in message news:1185467208.883054.107940@g4g2000hsf.googlegroups.com... > Hi > > Is it true that WindowsXP Pro has a 3GB limit on addressable RAM > space? > > We have a user who regularly uses spreadsheets of 1.5 to 2+GB in size > (on the hard disk). > - How much RAM should we give her? > - i.e. Is there any point in giving her over 3GB ? > > > Ship > > Shiperton Henethe2 If you have access to WXP 32-bit systems with various amounts of RAM, try this: Open device manager and in the View menu, choose 'View Resources by Type' on each of them. I think you will find that PCI memory starts at the end of physical RAM on systems with less than 3GB, and starts somewhere around 3GB with systems with greater than 3GB of physical RAMs, and that the end of the memory map is never greater than 4 GB (hex FFFFFFFF). On my 1GB system, here is my memory map: Memory Usage Summary: [000A0000 - 000BFFFF] PCI bus [000A0000 - 000BFFFF] VIA CPU to AGP Controller [000A0000 - 000BFFFF] NVIDIA RIVA TNT2 Model 64/Model 64 Pro (Microsoft Corporation) [000C0000 - 000DFFFF] PCI bus [40000000 - FFDFFFFF] PCI bus [D9C00000 - DDCFFFFF] VIA CPU to AGP Controller [DA000000 - DBFFFFFF] NVIDIA RIVA TNT2 Model 64/Model 64 Pro (Microsoft Corporation) [DDE00000 - DFEFFFFF] VIA CPU to AGP Controller [DE000000 - DEFFFFFF] NVIDIA RIVA TNT2 Model 64/Model 64 Pro (Microsoft Corporation) [DFFFF500 - DFFFF5FF] VIA Compatable Fast Ethernet Adapter [DFFFF600 - DFFFF6FF] Standard Enhanced PCI to USB Host Controller [DFFFF700 - DFFFF7FF] NETGEAR FA310TX Fast Ethernet Adapter (NGRPCI) [DFFFF800 - DFFFFFFF] VIA OHCI Compliant IEEE 1394 Host Controller [E0000000 - E3FFFFFF] VIA CPU to AGP Controller [FEE01000 - FFDFFFFF] PCI bus -Paul Randall
Guest Tim Slattery Posted July 30, 2007 Posted July 30, 2007 Re: Does Windows XP Pro have a 3GB limit on RAM ? "HEMI-Powered" <none@none.en> wrote: >Thank you. AFAIK, my ATI Radeon does not use main RAM. I don't >remember the fine details, but I think it is maxed out at 256MB. 256MB of the 4GB address space must be used to access the RAM on your video card. That 256MB of address space then cannot be used to access your main system RAM. So, installing that card means that you can't use any more than about 3.75GB RAM. Address space must also be used for the BIOS, and possible other things on PCI and PCIx cards, further reducing the amount of RAM you can actually access. -- Tim Slattery MS MVP(DTS) Slattery_T@bls.gov http://members.cox.net/slatteryt
Guest Dave Hahn Posted August 8, 2007 Posted August 8, 2007 RE: Does Windows XP Pro have a 3GB limit on RAM ? It's not necessarily a limit in the OS, its more about the limits of 32-bit computing. The total address space of any 32-bit processor is 4GB (addresses 0 to FFFFFFFF). What people get confused with is thinking that means that you can fill each of those address spaces with RAM. You can't. The reason? Memory mapped devices. Meaning that to talk to certain devices (DMA controllers, I/O controllers, really anything connected to the CPU), the CPU has to know what address the device is at. These devices consume address space just like RAM does. So, when you throw a couple dozen devices in the design, along with a video card that has a lot of on board memory (that typically has to be mapped into the CPU's address space), you start to lose the address space you'd like to put RAM into. As far as the virtual address space, Russinovich explains this in detail in Windows Internals. 2GB user space, 2GB OS space per process. If you are booted with the /3GB switch, then it's 3GB user, 1GB OS. David. "ship" wrote: > Hi > > Is it true that WindowsXP Pro has a 3GB limit on addressable RAM > space? > > We have a user who regularly uses spreadsheets of 1.5 to 2+GB in size > (on the hard disk). > - How much RAM should we give her? > - i.e. Is there any point in giving her over 3GB ? > > > Ship > > Shiperton Henethe2 > >
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