Fix Windows Not Using All RAM

If Windows is showing less usable RAM than you have installed—for example, 8 GB installed but only 5.9 GB usable—the fix usually involves checking for a hardware reservation, disabling the memory limit in System Configuration, or updating the BIOS. Start with the steps below in order; most cases are resolved by the first or second fix.

Why Windows Reports Less RAM Than Installed

Windows reports the total physical memory installed, but the “usable” amount can be lower for several reasons. The most common is a hardware reservation: integrated graphics chips (iGPUs) reserve a chunk of system RAM for video memory, which is normal and not a fault. Other causes include a 32-bit version of Windows (which caps usable RAM at about 4 GB), a physical RAM module not seated properly, or a BIOS setting that limits memory. In some cases, the System Configuration tool (msconfig) has a “Maximum memory” checkbox enabled, which artificially caps the amount Windows can use.

Before making any changes, open Task Manager (Ctrl+Shift+Esc) and go to the Performance tab, then select Memory. Look at the top-right: it shows “X GB” used and “Y GB” available. Below that, you’ll see a breakdown including “Hardware reserved.” If that number is large (e.g., 2 GB or more), it’s likely the integrated GPU or a BIOS reservation. If the hardware reserved number is small (under 100 MB) but the usable amount is still far below installed, the issue is likely software or a hardware fault.

Check the System Configuration Memory Limit

The most common software cause is a leftover setting in System Configuration. This happens when someone (or a guide) unchecked “Maximum memory” and then rebooted, or when Windows Setup leaves a value that no longer matches the installed RAM.

Press Win + R, type msconfig, and press Enter.
Go to the Boot tab and click Advanced options.
Uncheck the box next to Maximum memory (if it’s checked).
Also uncheck Number of processors if it’s checked—it can cause similar issues.
Click OK, then Restart when prompted.

After rebooting, check Task Manager again. If the usable amount jumps to near the installed amount, that was the fix. If not, continue to the next step.

Update BIOS and Check Memory Mapping

An outdated BIOS can misreport RAM or fail to enable memory remapping, which is needed for systems with more than 4 GB of RAM. Every motherboard has a BIOS/UEFI setting called Memory Remapping or Memory Hole Remapping. When disabled, Windows may only see the first 4 GB.

To update your BIOS, visit your motherboard manufacturer’s website and look for the support/download section for your exact model. Download the latest BIOS file and follow the manufacturer’s instructions—usually via a USB drive and the BIOS’s own update tool (often called EZ Flash, Q-Flash, or M-Flash). Do not interrupt the process; a failed BIOS update can brick the motherboard.

After updating, enter the BIOS (usually by pressing Del or F2 during boot) and look for a setting like Memory Remap, Above 4G Decoding, or Memory Hole. Enable it if it’s off, save, and reboot. This is particularly relevant for older motherboards or when using more than 4 GB of RAM.

Reseat RAM and Test Each Stick

If the software settings are fine, the problem may be physical. A RAM stick that isn’t fully seated, or a faulty slot, can cause Windows to see less memory than installed. This is more common after building a PC, moving a desktop, or cleaning inside the case.

Shut down the PC, unplug it, and open the case.
Remove all RAM sticks, then reinsert them firmly until the clips click. Make sure they’re in the correct slots per your motherboard manual (usually slots 2 and 4 for dual-channel, but verify).
If you have multiple sticks, test them one at a time. Boot with a single stick and check Task Manager. Repeat for each stick and each slot.

If a particular stick or slot shows less memory or fails to boot, that stick or slot may be faulty. If all sticks work individually but the total is still low when combined, check the motherboard manual for maximum supported RAM and slot configuration. Some boards only support up to 16 GB, or require specific slot ordering.

Check Windows Version and Hardware Reserved

Windows 10 and 11 are available in 32-bit and 64-bit versions. The 32-bit version has a hard limit of about 4 GB of usable RAM, regardless of how much is installed. If you have a 32-bit Windows, the only fix is to install the 64-bit version, which requires a clean install and a 64-bit processor (most CPUs from the last 15 years are 64-bit).

To check your version: go to Settings > System > About. Look at “System type.” If it says “x86-based PC” or “32-bit operating system,” that’s the issue. If it says “64-bit operating system,” then the limit is elsewhere.

Hardware reserved memory is shown in Task Manager’s Memory tab. On a typical desktop with a discrete GPU, hardware reserved is usually under 100 MB. On a laptop with integrated graphics, it can be 512 MB to 2 GB or more, depending on the BIOS setting. This is normal and not a problem. Some BIOSes allow you to adjust the amount of memory reserved for the iGPU (often called “UMA Frame Buffer Size” or “DVMT Pre-Allocated”). Reducing it frees up RAM for Windows, but may reduce graphics performance. Only change this if you understand the trade-off.

Run Windows Memory Diagnostic

If you suspect faulty RAM, Windows has a built-in tool. Press Win + R, type mdsched.exe, and press Enter. Choose “Restart now and check for problems.” The PC will reboot and run a memory test. The test takes 10-20 minutes. After it finishes, Windows boots and shows the results in a notification. If errors are found, replace the faulty stick.

This tool is basic; if it reports no errors but problems persist, you can use a third-party tool like MemTest86 (free, bootable) for a more thorough test. But for the “not using all RAM” issue, the diagnostic is a good second step after checking msconfig and BIOS.

Frequently Asked Questions

Why does Windows show “8 GB installed (5.9 GB usable)”?

That message appears in the System window when the usable memory is significantly lower than installed. It’s often due to hardware reserved memory (integrated graphics) or a software limit like the msconfig maximum memory checkbox. Check Task Manager’s Memory tab to see the “Hardware reserved” number. If it’s high, that’s the cause. If it’s low, check msconfig.

Can I disable hardware reserved RAM?

Not directly—hardware reserved memory is allocated by the BIOS and drivers for system devices. On systems with integrated graphics, you can reduce the reserved amount in BIOS (look for “UMA Frame Buffer Size” or “DVMT Pre-Allocated”), but you can’t eliminate it entirely. On desktops with a discrete GPU, hardware reserved should be minimal; if it’s large, update the BIOS or check for driver issues.

Is it safe to use msconfig to set the maximum memory?

No. The “Maximum memory” checkbox in msconfig is meant for debugging and should not be used as a permanent setting. If you check it and set a value, Windows will only use that much memory. Always leave it unchecked. If it’s already checked, uncheck it and reboot.

My PC has 16 GB but only 8 GB usable after adding new RAM. What’s wrong?

First, ensure the new RAM is compatible with your motherboard (check the manual for supported speeds and capacities). Then reseat both sticks, and test each stick individually. Also check if the motherboard supports dual-channel mode—sometimes using the wrong slots (e.g., 1 and 2 instead of 2 and 4) can cause the system to only see one stick. Update the BIOS if needed.

Does Windows 10 Home support more than 128 GB of RAM?

Windows 10 Home supports up to 128 GB on 64-bit versions. Windows 10 Pro supports up to 2 TB. If you have more than 128 GB and are on Home, you’d need Pro to use it all, but that’s an extreme edge case. For most users, the limit is hardware, not the OS edition.

Will adding more RAM always make my PC faster?

Not necessarily. If you already have enough RAM for your workload, adding more won’t speed things up. But if you’re running out of memory (Task Manager shows high usage and the system is slow), adding RAM can help. The “not using all RAM” issue is different—it’s about the OS not seeing installed RAM, not about performance.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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