I ordered some hard drives for an upcoming low-budget short film the other day. Due to budget constraints I couldn't exactly buy the "ideal" drives, but these will work fine nonetheless. I ended up with the following: (2) WD Caviar Blue 500GB (WD5000AAKS) 7,200-rpm (for camera data capture; 1 primary and 1 backup) (1) WD Caviar Black 640GB (WD6401AALS) 7,200-rpm (for editing and post) After unpacking the drives, I proceeded to run the AJA System Test on each drive to test the read/write speeds and noticed some interesting things. Being a nerd, I was simply curious. And just to preface, all three drives were blank and freshly formatted (Mac OS Extended), with no data previously written to them. Here's what I noticed: I ran the AJA Disk Read/Write test using a 4.0GB file size at the 1920x1080 10-bit video frame size - on all three drives. The two 500GB Caviar Blues both tested at around 130MB/sec (that's pretty fast), read and write. Just to be sure, I ran the test several times and consistently got the same results. But the 640GB Caviar Black didn't fare as well. That one consistently tested at around 103MB/sec. (still pretty fast for a single drive), read and write using the same testing parameters. But...really? The Blues are actually 21% faster? That's pretty significant. The only thing I can really gather regarding why this is actually the case would be somewhat anecdotal in nature: the 500GB Caviar Blues are noticeably lighter in mass, which may indicate these drives use fewer platters than the Caviar Black does. And fewer platters usually indicates higher aereal density, thus the faster transfer speeds. I made this post out of pure curiosity more than anything. Perhaps someone more versed in drive technology may be able to shed more light but I'm assuming my assumption with the number of platters is correct.