Higher read/write rates with compressed NTFS!?

[Silvije]

I just discovered the strangest thing! Since I’m having troubles with frame drops I tested my HD with the EZDV Test utility. I have four different partitions on my drive. I tested each of the partitions, and then noticed that one of them had a significantly higher read/write rate. What differed was that this partition was compressed. This puzzled me, because to my knowledge compression takes time! Just to make sure, I compressed another partition, and guess what! The read/write increased by a third! Then I changed the partition back to a non-compressed partition and the rates went back to the original rates. Is this possible? What is going on?

My system:
PIII 1Ghz
HD Maxtor 52049H3 (20Gb ATA-100)
256Mb RAM
Win2k on NTFS

Before compression:
Read 27MB/s
Write 26MB/s

After compression:
Read 86MB/s
Write 37MB/s

[NenoX]

What is going on?
Memory is much quicker than hard, so data is compressed in memory and then be writen to disk.

[Nelson37]

Previous answer not entirely correct. Speed difference is because you are spending less time writing data. Fast processors can compress the data to approx 50% in less than half the time it would take to write the original file, so you get faster performance. This performance gain is highly variable depending on file type, do same test with a group of EXE files and gain will be much less.