Why does Windows show less RAM than installed?

You may have noticed that your Windows OS may show that the usable memory may be less than the installed memory (RAM). For instance, your Windows OS 32-bit, may report that there is only 3.5 GB of usable system memory when 4 GB of memory has been installed. Or, a Windows OS 64-bit computer may show only 7.1 GB of usable system memory when 8 GB of memory may be installed.

Installed RAM vs Usable RAM

The indicative Usable Memory is a calculated amount of the total physical memory minus “hardware reserved” memory.

To view the installed memory and the usable memory in Windows 7:

• Click Start, right-click Computer, and then click Properties.

• View the Installed memory (RAM) value under System. For example, if it displays 4.00 GB (3.5 GB usable), this means that you have 3.5 GB of usable memory out of 4 GB of installed memory.

Windows shows less RAM than installed

The reduction in available system memory depends on the configuration of the following:

1. The devices that are installed in the computer and the memory that is reserved by those devices
2. The ability of the motherboard to handle memory
3. The System BIOS version and settings
4. The version of Windows OS that is installed
5. Other system settings.

Read: Find out Computer RAM, Graphics Card/Video memory of your Windows PC.

If, say, a computer has 4 GB of RAM installed, the system memory that is reported in the System Information dialog box in Windows is less. For example, the System Information dialog box may report 3,120 MB of system memory on a computer that has 4 GB of memory installed (4,096 MB). If a computer has many installed devices, the available memory may be reduced to 3 GB or less.

However, the maximum memory available in 32-bit versions of, say, Windows 7, is typically 3.12 GB. This behavior is the expected result of certain hardware and software factors. For Windows to use all 4 GB of memory on a computer that has 4 GB of memory installed, the computer must meet the following requirements:

• The chipset must support at least 8 GB of address space.
• The CPU must support the x64 instruction set. The AMD64 CPU and the Intel EM64T CPU support this instruction set.

The BIOS must support the memory remapping feature. The memory remapping feature allows for the segment of system memory that was previously overwritten by the Peripheral Component Interconnect (PCI) configuration space to be remapped above the 4 GB address line. This feature must be enabled in the BIOS configuration utility on the computer. View your computer product documentation for instructions that explain how to enable this feature.

Many consumer-oriented computers may not support the memory remapping feature. No standard terminology is used in documentation or in BIOS configuration utilities for this feature. Therefore, you may have to read the descriptions of the various BIOS configuration settings that are available to determine whether any of the settings enable the memory remapping feature.

There are several additional situations that could cause the usable RAM to be less than expected.

RAM supported by your Windows OS

How much RAM does each edition of Windows support? Windows 11/10 comes in different flavors—Home, Education, Pro, and Enterprise, and so the RAM supported varies.

Windows Server may support up to 24Tb.

How to increase the usable RAM on a PC

You may try the following suggestions to increase the usable RAM on your computer:

• Open the Boot Advanced Options in MSCONFIG and uncheck the Maximum Memory checkbox.
• Update the system BIOS and see
• Check BIOS settings
  • Enable the memory remapping feature
  • Change the AGP video aperture size in the BIOS settings
• Check the RAM for physical defects
  • Check whether you have bad memory modules
  • Make sure that the memory arrangement is correct
  • Check whether memory standoff cards are used.

Also read:

1. Physical memory allocation and memory status in Windows
2. Physical Memory Limits for Windows
3. Maximum memory (RAM) limit for 64-bit Windows.