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Ubuntu 10.4 64 bit OS - 8GB RAM is shown as 7.8GB - why? where is the rest gone? or is it just my math?

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I cannot believe it took 2 years for somebody to point out the fact there is a difference between GB and GiB – Ramhound Oct 18 '12 at 11:16

migrated from stackoverflow.com Jun 19 '10 at 9:33

3 Answers

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You might find the .2gb is being eaten by intergrated graphic or similar.

To find out where it's going run:

free -m
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hi thomas... free -m gives similar numbers (img248.imageshack.us/img248/4156/screenshot1dx.png) and the machine has a nVidia graphic card with dedicated memory. so, i'm kind of puzzled with the missing RAM. – user40460 Jun 19 '10 at 10:48
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the operating system and its data structures have to live somewhere: cat /proc/meminfo Don't worry, all your memory is there. Also there is the perennial confusion between GibiBytes and GigaBytes (for which I always have to puzzle out whether the SI or IEC prefixes are really meant). en.wikipedia.org/wiki/Gibibyte – msw Jun 19 '10 at 13:11
up vote 3 down vote

http://en.wikipedia.org/wiki/Gigabyte

gigabyte (GB) 10^9 2^30 gibibyte (GiB) 2^30

The manufacturer has supplied 8 * 10^9 Bytes of storage and marketed it as 8 GB.

8 GB * 1000 = 8000 8000 / 1024 (actual base two representation) = 7.8125 GB

Whats worse is if they actually did this the whole way:
8 * 1000 * 1000 * 1000 / 1024 / 1024 / 1024 = 7.45 GB

Its the same way with Harddrive manufacturers.

And ISPs: a 20 meg connection is 20 million bits not bytes. In reality since 1 byte = 8 bits, its only a 2.5 MB connection rate at maximum.

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This is the only correct answer. – Ramhound Oct 18 '12 at 11:17
up vote -3 down vote

It's due to the 3GB limit, PCI, AGP and PCIe and the hard drives, USB controller and any other PCI device you can think of.

This actually eats 0.5GB+ of RAM space but it's remapped higher in RAM space, above 8GB because Ubuntu supports 64GB (maybe only 16GB, but it's remapped). I'm guessing 1.2GB of RAM is eaten by PCI devices and 1GB is remapped.

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This is entirely incorrect from my knowledge.. – Simon Sheehan Oct 2 '11 at 5:54

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