I am using Ubuntu 18.04 and Window 10 on the same machine (dual boot) and recently I have upgraded the RAM from 4GB to 8GB. After that window-10 still used 4GB instead of 8GB. I had performed the "factory reset and reinstall window-10" to make Window 10 to use 8GB RAM. But now I am confused about is Ubuntu 18.04 using 8GB or 4GB of Ram? And have I to do reinstall ubuntu just like the window 10 so that it can use 8GB in ubuntu or some other actions.

I have attached some screenshots that clears the current state of RAM.

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  • I would have guessed that you used 32-bit Operating Systems, but your images indicate otherwise. – zx485 Aug 8 '18 at 22:09
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    Ubuntu is using all the 8 GB of RAM installed (see under total in free -m). At the moment when free was run, 4.6 GB of RAM were unused (free column) -- I suspect that the system was freshly rebooted. – AlexP Aug 8 '18 at 22:11

Your system is recognizing 8 GB of RAM on the system.

From your free -m output, the first column and row of the output ("TOTAL") indicates your total RAM of 7881 MB (which is not atypical when you install 8GB of RAM).

Of that 8GB, your system is using approximately just over 2GB for buffers, cache, shared memory storage, and actually in-use resources (used + shared + buff/cache).

The "Available" column tells you how much RAM is actually available to be allocated, because the "shared" and "caches" aren't actually always "used" space. This means you have about 5573 MB (just over 5.5GB) of memory available on your system.

So your system is seeing the 8GB of RAM, but is using about 2GB of space already.

You should probably read about how Linux uses RAM and how to interpret free -m output here, on linuxatemyram.com, to better understand what's actually being used in the RAM.

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