What does 'calculate image checksum crc-32 and md-5 mean?

Discussion in 'Mac Basics and Help' started by sophie8, Sep 2, 2009.

  1. sophie8 macrumors newbie

    Jul 31, 2009

    Whenever I open disk utility, I need to choose between 'calculate image checksum (CRC-32)' and ' calculate image checksum (MD-5)' before I can open disk utility. I always click on either one of them because otherwise disk utility won't open. I am wondering what it means. I called the Apple support about it, but the girl on the phone didn't see it on her computer and couldn't find any info about it. Maybe one of you could help me out? Thanks!
  2. savar macrumors 68000


    Jun 6, 2003
    District of Columbia
    I'm not familiar with that screen, but checksums are a way of summarizing a large amount of data in small amount of space. This is used for making sure that large files have not been modified while being copied or transmitted. If you download an entire CD or DVD from a website, for example, they usually include the MD5 checksum.

    When you get the download completed, you calculate the checksum on your end and match it against the one the download site provided. If the file differs from the original by even a single bit, then the checksum will be noticeably different.

    It's just a short way to check that two copies of something are identical.
  3. sophie8 thread starter macrumors newbie

    Jul 31, 2009
    Thanks for your answer! I am transferring lots of music files at the moment (160 GB) from my pc to two external hard drives. So from one pc to an external hdd and from that external hdd to another external hdd. Is is possible to apply checksum to my pc and the two hard drives?

    What is the difference between crc-32 and md-5?

    So you don't see that screen either. Maybe there should be a way to disable it.

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