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I have 512MB RAM in my PC. Ubuntu detects only 495 MiB. How can I fix this?

On Debian Squeeze, I was have 512MB.(The correct size)

OS: Ubuntu 12.04 Precise Pangolin

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How are you measuring it? – psusi Jan 26 at 14:44

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up vote 4 down vote accepted

Your RAM is detected correctly. MB (megabyte) and MiB (mebibyte) are two different units.

  • 1 MB is 1000 KB which is 1000 byte (decimal)
  • 1 MiB is 1024 KiB which is 1024 byte (binary)

If you check the math yourself you will see that 512 MB are 495 MiB ;-)

MB is mostly used for selling stuff because it's the higher number. In your Ubuntu system you will mostly encounter MiB (or GiB).

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@stonedsquirrel Thanks! – Sebastian Jan 26 at 14:38
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If this were the case, then 512 MB of ram would be 488 MiB, not 495. Ram modules come in powers of two, so 512 MB is 512 * 1024 * 1024 bytes, not 512 million bytes. It is just hard drive vendors that lie and use powers of 10 to make their drives look larger. – psusi Jan 26 at 14:46
@psusi Alright that's strange. I didn't do the math myself as I am used to that offset and never really think of it anymore. I have also seen it with RAM many times, not only hard drives. – stonedsquirrel Jan 26 at 14:53
@stonedsquirrel, nope.. ram modules always comes in even powers of two. Any less reported than you physically have is overhead of some kind, such as the kernel or bios reserved memory. – psusi Jan 26 at 21:38
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