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Whats the differnce between SATA II (3 Gb/s) and SATA III (6 Gb/s) Hdds


Im using a Lenovo T520 myself.

I looking for all round laptop sata hard drives.

On a supplier site I see....

SATA II (3 Gb/s)  and SATA III (6 Gb/s)  Hdds

Should I just go for SATA II .  Im buying several for laptop repairs.

4 Solutions
JohnBusiness Consultant (Owner)Commented:
You can use either drive, but go for the drive with the largest cache.

Now, I am not an expert in this, but in researching a new drive for my ThinkPad X230, I was led to believe that a hard drive won't use all the bandwidth of a SATA II interface, so then will not use all the bandwidth of SATA III, but SATA III will work.

I am looking a putting a Western Digital 1Tb drive in my machine.

... Thinkpads_User
If you have a mechanical HDD then it can't saturate a SATA-II interface, let alone a SATA-III.   So you are throwing your money away paying extra for a HDD with a SATA-III interface.   Not only that, but some laptops won't support SATA-III anyway.

When searching for a replacement disk, the most to least important should be ...
1. Verify physical dimensions are OK.
2. Make sure new disk does not generate more heat (BTUs) then the one you are replacing.
3. Same for power.  If it draws more power then you may still be OK, but battery life will suffer accordingly.
4. Do NOT get advanced 4K sectored disks.  Get 512 byte sectored drives.
5. Warranty.
6. Shock resistance
7. Number of ECC bits (error correcting)
8. Capacity
9. Random I/O read & write performance
10. Sequential read & write performance (uncached)
11. Same as above, but cached.
12. MTBF
13. Physical interface

(I am purposely avoiding price, because in the grand scheme of things your data is going to be worth whatever delta there is between drives in your price range anyway).

The amount of cache is irrelevant because #10-11 are real-world numbers and factor in both the amount of cache and seek time  & RPMs.
The Lenovo T520 supports SATA 3. I don't know what the cost difference is, how many you're planning on buying, or what exactly you'll be doing with them but maybe SATA 3 is overkill.
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Gary CaseRetiredCommented:
No rotating platter hard drive -- even the 1TB/platter units (which are only on desktop drives) can come close to a sustained transfer rate of 300GB/s ... which is the SATA-II rate.

So for most data transfers it makes ZERO difference whether or not your interface is SATA-II or SATA-III.

There is one very minor caveat:   transfers to/from the cache on the drive DO occur at "interface speed" ... so these will be slightly faster on a SATA-III unit if it's connected to a SATA-III controller (many laptops only have SATA-II controllers).

But buffer <-> disk transfers are a VERY tiny % of the actual transfers ... so the actual difference in performance is barely measureable ... and certainly NOT noticeable.

Bottom line:  SATA-II units are fine for rotating platter drives.   I presume that's what you're buying, so I wouldn't worry about which interface they have -- if the SATA-II units are cheaper, just get them.    SSDs are, of course, another story, since they can indeed exceed the SATA-II transfer rate.    But even there, unless the laptop has a SATA-III interface, it wouldn't matter.
fcekAuthor Commented:
Thanks everyone.

After another long day I shall order the correct parts and hit the hay.

After a juicy well earned pint of Guinness :-)
Nobody is shipping high capacity drives with 512byte sector count anymore ,it's all 4k,so it is what it is.

As for the SATA III interface,it's basically about burst rates between the HDA and onboard controller.

You will not get sustained 6gb from SATA III or 3gb from II.

SAS and SCSI can give you a sustained throughput close to their intended spec,but not SATA.
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