Will a csv file load faster in excel when its not ntfs compressed?

Yes, a CSV file will almost always load faster in Excel if it is not NTFS compressed.

Here’s a breakdown of why this is the case:

How NTFS Compression Works

NTFS compression is a feature of the Windows file system. When you compress a file or folder, the operating system saves it in a smaller format on the disk. This is done to save storage space. To do this, the system's processor must perform a real-time operation: it decompresses the data from the disk every time it is read and compresses it again every time it is written.


The Impact on Excel

When Excel loads a compressed CSV file, the process is not as simple as just reading the data off the disk. The sequence of events is as follows:

Read Request: Excel requests the file data from the operating system.


CPU Decompression: The NTFS file system intercepts this request and tells the CPU to decompress the data as it's being read from the disk. This adds a processing step that wouldn't exist for an uncompressed file.


Data Transfer: The decompressed data is then transferred to Excel.

Even though modern CPUs are very fast, this decompression step adds a measurable amount of overhead to the loading process. For very large CSV files, this extra work can make a noticeable difference in load time.

In contrast, when you load an uncompressed CSV file, Excel can read the data directly from the disk without any intermediate CPU-intensive step. This makes the data transfer process more efficient and quicker.


When to Use Compression

The trade-off is between storage space and performance. If you have a file that you need to store but don't access frequently, NTFS compression can be a great way to save disk space. However, if you're working with a file, like a CSV that you open often, it's best to leave it uncompressed for faster access.

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