|True, the WD green series is not as high performance as, say, a WD Black, but it is by no means slow. |
According to Western Digital, the drive has a maximum sustained read/write of 150 MB/s, although in real world benchmarks it seems to be more like 100 - 110 MB/s.
It is also true that it is usually used for secondary storage (usually of various media) rather than a main drive. It generally has a lower cost per gigabyte than higher performance drives, and so you can get more storage capacity for the same price.
The slower performance does not necessarily mean that this drive will be bad for gaming. The only effect it will have is on loading times of programs, and will not hurt your in game FPS.
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