Why is Linux only showing 251GB Total Memory?

[Fritz]

BIOS and Superdoctor are showing 256GB which is correct.

 

[zac1]

System reserved/graphics?

Why does Ubuntu show slightly less RAM than my computer has built in?

My machine's RAM is 8 GB. I have recently installed Ubuntu 17.04. Why does Ubuntu show me that it has only 7.7 GB and not the full 8 GB?

askubuntu.com

 

[Fritz]

Thanks. Video card is an add in, GeForce GTX 750 Ti. Onboard video is disabled.
I'm assuming that since both the BIOS and Superdoctor are reporting the correct memory the issue is with Linux.

EDIT: Also, I'm assuming that "TOTAL Memory" does indeed mean Total Memory but I could be wrong.

 

[zac1]

The linux kernel reserves memory at boot. Some is never available to be used except by the kernel, so "total" memory reported by free et al will never correspond 1:1 with physically installed.

free derives its data from /proc/meminfo. This page has a nice breakdown of the metrics: https://www.baeldung.com/linux/proc-meminfo

 

[Fritz]

Ah, now I understand. Total does not mean total in Linux. Thank you sir.

 

[zac1]

Ah, now I understand. Total does not mean total in Linux. Thank you sir.

It totally depends on context. The kernel requires a minimum amount of memory to remain useful. In the context of a running Linux system, it makes sense that "total" only includes usable memory. No point in counting the memory the kernel is never going to let go of.

dmidecode can be used to query the size of the physically installed DIMMs.

https://www.baeldung.com/linux/total-physical-memory#2-using-dmidecode

 

[Fritz]

It totally depends on context. The kernel requires a minimum amount of memory to remain useful. In the context of a running Linux system, it makes sense that "total" only includes usable memory. No point in counting the memory the kernel is never going to let go of.

dmidecode can be used to query the size of the physically installed DIMMs.

https://www.baeldung.com/linux/total-physical-memory#2-using-dmidecode

Yes sir, I have adjusted my understanding of "Total" in regards to Linux.