How does SATA II and SATA III work?

[nickspacemonkey]

Hi all!

Ok, so i get that SATA II is 3Gb/s and SATA III is 6Gb/s, so there's the difference. SATA III is twice as fast. But here is what i don't understand:

• A SSD read and write rate is ~500mb/s.
• So if the SSD was reading and writing at the same time it would theoretically be transferring data at ~1Gb/s.
• So SATA II should be capable of utilizing the drive to it's full potential as it is capable of transfer rates of 3Gb/s.

Am i wrong in this assumption? Well obviously i am because there has to be some benefit to SATA III I'm just not seeing it

I have a old rig I'm replacing/upgrading soon and i wanna clear up the difference as other posts I've read seem rather vague. They all just seem to want to know if SATA III drives are backwards compatible.

Thanks for the your time and for enlightening me.

 

[freakdiablo]

I think you are getting your lower case bs and upper case Bs mixed up. A lower case b stands for a bit, and an upper case B is a byte. One byte is 8 bits. What this means is a good SSD will transfer at around 500MB/s if not more, which is 4Gb/s , which will be limited by SATA II. But, a SATA II drive will work in a SATA III port and a SATA III drive will work in a SATA II port, it'll just be slowed to that 3Gb/s cap.

 

[Dermen]

bits (b) and bytes(B) . SataII is 3gigabit (Gb/s), SataIII is 6gigabit (Gb/s). SSD read/write is 500 megabyte (MB/s).

8 bits in a byte, so 500MB/s is 4000Mb/s or 4Gb/s.

There is also overhead, they list the theoretical max but it is not obtainable in real usage. The best SataII controllers/drives seem to top out around 280MB/s, or 2.2Gb/s. I think the best SataIII is around 550MB/s, or 4.4Gb/s.

 

[petteyg359]

There is also overhead, they list the theoretical max but it is not obtainable in real usage. The best SataII controllers/drives seem to top out around 280MB/s, or 2.2Gb/s. I think the best SataIII is around 550MB/s, or 4.4Gb/s.

The overhead is already included in the numbers (assuming k is 1000, rather than 1024). 3 Gbps is 375 MBps, and you multiply by 0.8 (for the 8/10 encoding) to get 300 MBps. 6 Gbps is 750 MBps, for 600 MBps. Hence, SATA II is sometimes advertised as SATA 300, and SATA III as SATA 600.

 

[Anonaru]

The overhead is already included in the numbers (assuming k is 1000, rather than 1024). 3 Gbps is 375 MBps, and you multiply by 0.8 (for the 8/10 encoding) to get 300 MBps. 6 Gbps is 750 MBps, for 600 MBps. Hence, SATA II is sometimes advertised as SATA 300, and SATA III as SATA 600.

Beautiful. I've seen 575 on SATA III as an absolute max in my time. I really don't know why bps is used in computing anymore. I understand it became the bandwidth standard eons ago but we're so far beyond the bit that measuring anything as such is stupidly redundant. All saying "1Gbps LAN" and "480Mbps USB" does is make the end user go "I don't get anything close to that."

Derp.