I have upgraded Windows and the RAM memory on my desktop PC. I've installed 4GB of RAM and Windows 7 Home Premium (64-bit version), which is supposed to be able to address 128GB of memory, but only 2.7GB is reported as usable. The PC has an Intel Pentium 4 3.6GHz single-core processor and a DFI LanParty 925X-T2 motherboard with an Intel 925X chipset and a GeForce 8800GT graphics card.

Answer

A 32-bit version of Windows can only use about 3.5GB of RAM memory. Only the 64-bit versions of Windows can use 4GB and more of memory. Even with a 64-bit version, for Windows 7 (or Windows Vista) to use the full 4GB of memory, the computer must meet the following requirements:

1. - A 64-bit version of Windows must be used. (Most PCs still use 32-bit versions of Windows.)

2. - The processor must support the x64 - 64-bit - instruction set. (Most processors dating from 2006 do. To find out if a particular processor does, visit the Processors section of this website.)

3. - The motherboard's chipset must support at least 8GB of address space. Intel chipsets that have this capability include 975X, P965, 955X, which are all Intel Socket LGA775 chipsets, and all chipsets for Intel Sockets 1366 and 1156. AMD chipsets that use Socket 940, 939, AM2, AM2+ and AM3 also support 8GB of address space, which means any AMD processor dating from 2005 does.

4. - The system's BIOS setup program must support memory remapping, which allows the segment of system memory previously overwritten by the PCI configuration space to be remapped above the 4GB address line. This feature must be enabled in the BIOS. It can be difficult to locate, since, for some strange reason, there is no standard terminology for memory remapping .

Only a few Intel Pentium 4 (single-core) processors support 64-bit instructions. Fortunately, yours, one of the last Pentium 4 CPUs made, using the Prescott 'F' core, does . However, memory mapping remains a problem. With modern versions of Windows such as Windows XP, Windows Vista and Windows 7, large areas of memory between 3GB and 4GB are reserved for system devices. The processor and other peripheral devices can communicate with other devices by reading and writing memory addresses into these reserved areas.

The largest slice of memory is usually reserved for the graphics card(s). The graphics card's onboard graphics RAM memory has to be mapped to the main system RAM memory, byte for byte. Therefore, if the graphics card has, say, 512MB of memory, 512MB is unusable by Windows. If you were to install two nVidia GeForce 7950 GX2 graphics cards that have 1GB of graphics memory each 2GB of RAM would not be accessible by Windows.

If your hardware and software were all 64-bit compatible, this mapping problem becomes less significant. It looks as if your motherboard's BIOS doesn't support memory mapping or the feature is disabled. If you can't find the option, look for a BIOS update on DFI's website. The current version's ID is provided on the startup screen if it is the one that provides a memory count, not the computer-manufacturer's logo. The free Belarc Advisor from http://www.belarc.com/ provides the BIOS version. If there is a higher version, you might be in luck.

Computer diagnostics: How to solve or fix common desktop and laptop PC problems

To diagnose and troubleshoot specific and general problems with Microsoft's software (Windows 95, 98, Me, XP, Vista, Internet Explorer, and Outlook Express) using the MS Knowledge Base, visit the Diagnostics page on this site.

Click a relevant link below to visit the information it describes on this website:

1. - Recovering and repairing Windows XP when a computer crashes or fails to boot

2. - Recovering and repairing Windows Vista when a computer crashes or fails to boot

3. - Windows Vista problems: How to fix problems with Windows Vista

4. - Recover, restore and repair Windows 7 (Win7) when a computer crashes or fails to boot

5. - Windows 7 problems: How to diagnose and fix problems with Windows 7

6. - Windows XP: How to troubleshoot and fix shutdown, restart (reboot), and startup problems

7. - Typical DLL (Dynamic Link Library) device driver problems

8. - Software problems: How to fix problems with Windows, programs, and utilities

Also visit the Software pages on this site for more information on specific software-related information and problems.

9. - Motherboard and power supply problems: How to fix common problems with faulty motherboards (mainboards) and power supplies (PSUs)

10. - RAM memory problems: How to fix problems with the Random Access Memory

11. - Hard disk drive problems: How to fix computer hard disk drive (HDD) problems

12. - CD/DVD drive problems: How to fix problems with CD and DVD drives and discs

13. - Processor problems: How fix common processor (CPU) problems

14. - Video/graphics card problems: How fix common computer video and graphics problems

15. - USB and FireWire problems: - How to fix common USB and FireWire problems

16. - Network problems: How to fix common wired and wireless networking and internet problems

17. - Laptop/notebook problems: How to address or fix the most common laptop/notebook problems

How to fix problems with device drivers in Windows XP and Windows Vista and Windows 7

Although the information on the following page is specific to Windows XP, much of the advice is relevant to the earlier versions of Windows. Click here! to read Troubleshoot Device Driver Problems. Click h ere! to go to Tips for fixing common driver problems in Windows Vista. Those tips should also be applicable to Windows 7.

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Visit the Build a PC page for information on how to build a desktop PC and solve self-build problems, and visit the other pages, such as the Video/Graphics, Sound, Motherboards, and Monitors pages for more problem-solving information, all of which can be accessed via the menu items and jump menu on the orange navigation bar, or via the site search engine at the top of each of the main pages.

The Tips & Tricks pages of this site contain additional useful tips, tricks, and problem-solving advice.

The safest way to upgrade RAM memory: Use the UK and US Crucial Memory Advisors

Paul Mullen, who was the highly-respected computer guru of the Helpfile at ComputerShopper.co.uk - "I have recently been buying my memory only from Crucial Technology. I would rather pay the extra cost than waste time trying to track down the obscure program faults that bad memory can cause."

The best way to choose RAM memory for a brand-name desktop or laptop computer, or memory for a particular make/model of PC motherboard is to make use of the Crucial Memory Advisors (provided under the brief guideline on the minimum memory requirements for Windws XP, Windows Vista and Windows 7). If the Crucial memory you receive does not work, you are guaranteed a refund and standard shipping is free.

The memory requirements of the versions of Windows Vista and Windows 7

Most of the versions of Windows Vista require more RAM memory to run optimally on a computer that doesn't use memory-hungry applications than Windows XP. A video-editing application is an example of memory-intensive software. Only Windows Vista Home Basic has a recommended minimum amount of memory of 512MB, which is the same amount recommended for Windows XP. Windows Vista Home Premium, the most popular version, and Windows Vista Ultimate require a recommended minimum of 1GB (1024MB) of memory, which is twice the amount of minimum memory recommended to run Windows XP. Note that if you are using a 64-bit version of Windows, up to 4.0GB, it requires twice the amount of memory as a 32-bit version, which can only use a maximum of about 3.5GB. For more information on computer memory, read the RAM pages of this site, which includes information on the lower memory requirements of Windows 7.

UK - Crucial Memory Advisor - UK

USA - Crucial Memory Advisor - USA

How to Use the Crucial Memory Advisor

For example, if your computer has an Asus motherboard, open the menu, scroll down to ASUS, and click GO. If, say, you have a Dell computer, scroll down to DELL, and do likewise. You will be taken to the relevant information on Crucial's website.

If you don't know the make and model of the motherboard installed in your computer, here is a good free utility - Belarc Advisor - that creates an analysis of the hardware and software on a personal computer. Look under FREE DOWNLOAD - http://www.belarc.com/. Another utility that also provides detailed information on the memory itself is CPU-Z.

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