Hard Drive data rates

Lamar Owen lowen at pari.edu
Fri Sep 28 18:08:28 UTC 2007


On Friday 28 September 2007, Karl Larsen wrote:
>     I was lead to mis-understand the data rate of my new SATA hard
> drive. It indicated that the data rate was 3 GB/sec. But some checking
> with Google said the Hard Drive makers are very free with their units.
> To be specific a SATA drive is 3000 MegaBits/second. This boils down to
> about 375 MB.

Due to the 8B/10B coding used in SATA, you can divide the bitrate by ten and 
not eight to get the byterate.  Thus, 3Gb/s is 300MB/s at the wire. The 
semi-standard way of differentiating between bits per second and bytes per 
second in specs is to use a lower-case b for bits, and an upper-case B for 
bytes, but unfortunately not everyone follows that. 
-- 
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu




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