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    Trim: The Basics

    Apple recently announced Trim support for all SSD-capable Macs.  What is Trim?

    The SSSI Glossary defines the Trim command as “A method by which the host operating system may inform a NAND Flash-based SSS device about which blocks of data are no longer in use and can be erased. Such blocks may then be written without having to erase them first, enhancing SSS device write performance.”

    A drive’s internal Garbage Collection performs a similar task as Trim by erasing blocks that have been previously marked for deletion.  However, because of the way that many operating systems work, there will be some blocks that can be repurposed of which only the OS is aware; Trim addresses this issue.

    For Trim to be functional, both the SSD and the OS must support it.  Most SSDs of recent vintage support Trim, but check the features list to be sure.

    In addition to the Apple OS, anyone who’s been paying attention knows that Microsoft Windows 7 supports Trim.  And an increasing number of Linux versions support Trim, plus FreeBSD and OpenSolaris.  Wikipedia has a more detailed list.

    2 responses to “Trim: The Basics”

    1. Satheesaran says:

      When TRIM is issued from OS to the SSS device, it means that OS informs SSS Device about the unused spaces (blocks or pages)in it. So this enhances performance. But I have read like the behavoir of N-Channel MOSFET is like, it should be however erased before we program. Suggest me whether i am wrong or there are some hidden facts in it

    2. Team_SSSI says:

      You are correct that a Flash cell must be erased before it is written. Trim tells the SSD which previously written locations no longer contain valid data, so that the SSD can erase those locations. Then the next write to any of those locations does not require erasure first, thus improving performance.

      Thanks for your comment.

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