Happy to Verify Compatibility
If you like, you can tell us the brand and full model number of the computer -or- motherboard you need memory for and we will be happy to double-check compatibility for you.

Happy to Direct to Compatible Memory
If you like, you can tell us the brand and full model number of the computer -or- motherboard you need memory for and we will be happy to direct you to the correct memory for your system.

Locate HP Model Number
You should see a label with the HP logo on it on the underside of the computer. You may need to remove the battery to find it. The number near "service tag" would be your full model number. If this is not present, we are able to cross-reference the product number (p/n), which usually ends in "#ABA", from this same label.

Locate Toshiba Model Number
You can find the full model number on a label on the underside of the computer, directly under the Toshiba name at the upper left of the label.

Apple Model Identifier
You can usually find the Model Identifier of your system by clicking on the Apple, then selecting "About This Mac", clicking on "More Info", then clicking on "Hardware" in the left pane. The Model Identifier should be listed under "Hardware Overview" in the right pane.

Manufacturer installed higher speed memory
Computer manufacturers such as Dell typically only carry the fastest speed of memory available in any generation (such as DDR, DDR2, or DDR3), knowing that it will step down to slower speeds as needed for the sake of compatibility. This helps them simplify their parts inventory. This is why your system has PC2-6400 DDR2 800MHz memory installed instead of the specified PC2-5300 DDR2 667MHz memory.

32-bit versus 64-bit Memory Capability
Of course, be aware that 32-bit versions of Windows cannot access more than 4GB of memory, regardless of the hardware's memory capacity. You would need a 64-bit version of Windows to access memory beyond 4GB.

4GB limit regardless of 64-bit version of Windows
This is a hardware limitation and would not be affected by the use of a 64-bit version of Windows.

Mac Pro ECC Registered Memory
Please be aware that the memory in this listing is ECC Registered, whereas the factory memory in your system is ECC Unbuffered. Your system can use either type, but not both at the same time. You would need to remove the factory memory before installing this memory. We recommend ECC Registered memory in the 8GB module size and higher for increased stability.

Quad-Ranked vs Dual-Ranked Explanation
As a means of explanation, quad-ranked 4GB modules are comprised of four 1GB chipsets, while dual-ranked 4GB modules are comprised of two 2GB chipsets.

Less than 4GB reported in 32-bit Windows
All versions of Windows reserve a varying amount of memory off-of-the-top for internal functions such as video memory and other internal motherboard functions. Most of the time, the user does not know this because Windows simply reports the actual memory capacity of the system, with a varying amount of memory still being reserved in the background. However, when using a 32-bit version of Windows with a system that has 4GB of memory installed, Windows will actually report less than the 4GB of memory as usable, with the remainder under this reservation. Please rest assured that this is completely normal and expected.

If you access your system’s BIOS, it should report all 4GB as installed.