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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 have 512MB.(The correct size)

OS: Ubuntu 12.04 Precise Pangolin

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

2 Answers 2

up vote 7 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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en.wikipedia.org/wiki/Mebibyte –  Merlin Jan 26 '13 at 14:32
    
@stonedsquirrel Thanks! –  Sebastian Jan 26 '13 at 14:38
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

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.

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

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