SATA-Disk Module 4

APSDMxxxxX5AN-PXXX

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© 2013 Apacer Technology Inc.

Rev. 1.3

5.6 TRIM

TRIM, though in capital letters usually, is a memory computation command rather than an abbreviation. It

is mainly a SATA command that enables the operating system to inform the SSD (Solid State Drive)

which blocks of previously stored data are no longer valid, due to erases by the host or operating system,

such as file deletions or disk formatting. Once notified, SSD will begin the discard of the invalid LBAs and

retain more space for itself, in fact, the discarded is no longer recoverable.

When an LBA is replaced by the operating system, as with overwrite of a file, the SSD is informed that the

originally occupied LBA is determined as no longer in use or invalid. The SSD will not save those blocks

in garbage collected sectors. Noticeably, a file deletion command by host or operating system never

actually erases the actual content, rather, just the file is marked as deleted. This issue is even specifically

noticeable for flash based memory devices, such as SSDs. In fact, an SSD will keep garbage collecting

the invalid, previously occupied LBAs, if it is not informed that these LBAs can be erased. Thus, the SSD

would experience a significant performance downfall.