如果您正在尋找調整Windows系統以節省磁碟空間的方法，則可以選擇NTFS壓縮。但是如果你選擇這個選項，那麼解壓過程是如何工作的呢？今天的超級使用者問答帖子回答了一位好奇的讀者的問題。

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，是一個由社群驅動的問答網站分組。

問題

引發UnderflowSeveryWhere的超級使用者讀取器想知道NTFS壓縮檔案是否解壓縮到磁碟或記憶體：

How does NTFS decompression work in Windows? According to Microsoft, NTFS decompression is done by expanding the file, then using it. That sounds right, but my question is how does this process occur technically?

Does Windows load the compressed file into memory, expand it in memory, then read it from memory? Or does it load the compressed file into memory, expand it to disk or memory, write it to disk, then read it?

I am trying to figure out if I can improve my computer’s performance by using NTFS compression. That way, a slow hard drive or SSD that is unable to handle that many write operati*** will always have less data to write and read, and the powerful processor that is idling most of the time can decompress the files and improve my computer’s storage speed and health.

NTFS壓縮檔案是否解壓縮到磁碟或記憶體？

答案

超級使用者貢獻者Ben N為我們提供了答案：

Windows decompresses files into memory. Doing it to disk would completely obliterate any speed improvements and would cause a lot of unnecessary disk writing. See the end of this Microsoft blog article on NTFS sparse files and compression.

Of course, if you are low on memory, the memory used by the decompression process could cause other memory be paged out and written to disk in the page file. Fortunately, only the chunks containing secti*** that your programs actually read will be decompressed. NTFS does not have to decompress the whole thing if you only need a few bytes.

If your SSD is fast, you are probably not going to get any speed improvements from NTFS compression. It is conceivable that the time your processor spends decompressing data plus the time your disk spends reading the compressed data could add up to be more than the time your SSD takes to read the uncompressed data.

It also depends on the size of the files you work with. The minimum size of a compressible file ranges from 8 – 64 KB, depending on your cluster size. Any files less than that in size will not be compressed at all, but a tiny amount of bookkeeping would be added. If you do a lot of writing to compressed files, you could see a lot of variance in speed due to the compression algorithm used (LZ).

Further Reading

How Does NTFS Compression Affect Performance?

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圖片來源：Jannis Andrija Schnitzer（Flickr）