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

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

OS: Ubuntu 12.04 Precise Pangolin

  • How are you measuring it? – psusi Jan 26 '13 at 14:44

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).

  • en.wikipedia.org/wiki/Mebibyte – Moog Jan 26 '13 at 14:32
  • 1
    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 '13 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. – André Stannek Jan 26 '13 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 '13 at 21:38
  • @psusi Good to know. My bad! Sorry for that! – André Stannek Jan 26 '13 at 22:05

a) At startup, the BIOS counts the number of working RAM-bytes, but EXCLUDES the ram-bank used for the test. That difference is fully normal. -- b) Any faulty RAM-bank is neither used nor counted. In that case, the computer can still be used for non-important jobs.

  • This is true but wrong, and doesn't apply here – Tim Aug 17 '14 at 15:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.