Why does Linux 4g memory only recognize 3.0?

Linux 4g memory only recognizes 3g. The reasons are: 1. Memory addressing space limitations. 32-bit operating systems, such as early versions of Linux, have a 4GB memory addressing space limit, part of which is the memory address space. Reserved for other hardware devices; 2. Memory mapped IO area. Some hardware devices need to use a part of the memory address space for memory mapped I/O operations. These areas are reserved and allocated to these devices.

The operating system of this tutorial: Linux5.18.14 system, Dell G3 computer.

In a Linux system, if your computer has 4GB of memory, but only 3.0GB is shown as available, this may be due to the following reasons:

1. Memory Addressing space limit:

32-bit operating systems (such as early versions of Linux) have a 4GB memory addressing space limit. Among them, part of the memory address space is reserved for other hardware devices, such as graphics cards, sound cards, etc. Therefore, the operating system can only use the remaining address space to address memory, which may result in some memory not being fully recognized and used.

2. Memory mapped IO (MMIO) area:

Some hardware devices (such as graphics cards) need to use a part of the memory address space for memory mapped I/O operations. These areas are reserved and allocated to these devices, so this part of memory cannot be used by the operating system for system memory.

The above situation causes a part of the memory to be unused by the system, resulting in the actual available memory being less than the total memory capacity. This may have an impact on system performance, for example it may cause the system to run slower or be unable to run large applications simultaneously.

To solve this problem, you can try the following methods:

• Upgrade to a 64-bit operating system: If your computer hardware supports a 64-bit operating system, consider upgrading to 64-bit Linux distributions. The 64-bit operating system can better utilize large-capacity memory and fully recognize and use more than 4GB of memory.

• Kernel parameter settings: You can try to solve the memory limit problem by modifying the Linux kernel parameters. For example, add or modify the mem or memmap parameters in GRUB or sysctl settings at startup so that the system can correctly identify and use more memory. The specific setting method depends on the Linux version and kernel you are using. It is recommended to consult relevant documents or forums for more accurate guidance.

• Check hardware and BIOS settings: Make sure your computer hardware and BIOS settings do not have any restrictions or memory-preserving settings. Some computers may have specific BIOS options that configure the memory size and address space allocated to the device. Checking these options and adjusting accordingly can help the system better recognize and utilize memory.

Please note that before making any changes, please back up important data and make sure you have sufficient understanding of the system settings and configuration. If you are not sure how to operate, it is recommended to consult a professional or refer to relevant documentation.

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