www.nikonimgsupport.com/Understanding RAW Files
Type of NEF(RAW) available...
Lossless Compressed
This method uses a compression algorithm that is reversible...
Compressed
This method also compresses the data to reduce its size on the card but this method uses a non-reversible algorithm. Therefore data that has been removed from the image cannot be restored later.
Compressed is most useful where available space is an issue on cards but the NEF format is still required.
HE/HE* (High Efficiency) compressed
This method uses the latest, high efficiency codec to compress the data to reduce its size on the card. Although this method uses a non-reversible algorithm similar to compressed mode, the result is a smaller file size while maintaining the same quality, effectively making this more ideal solution.
HE modes are most useful where a large numberof images are expected in a continuous burst sequence, allowing a high-mega-pixels camera such as the Nikon Z 9 to capture extensively and at a higher speed without overflowing the buffer.
The file size that is recorded in the camera is dependent on the type of RAW compression used. The chart below shows the percentage of reduction in file size depending on which method of storing the file is used...
Loseless Compressed - 20 - 40%
Compressed - 35 - 55%
HE/HE* - 50% to 70%