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Stupid Gb/s question on hard drives

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April 29, 2010 3:48:21 AM

Okay, I know this is a dumb question but I cannot find any answers by searching. What is the difference between 3.0 Gb/s and 6.0 hard drives? Yes, the speed, but can they go up to 6.0? I am not even certain if they can.

Thanks for the help. The answer is bugging me.
a c 415 G Storage
April 29, 2010 6:02:42 AM

It means the connection between the drive and the motherboard can carry 3 or 6 billion bits per second (equivalent to about 300 or 600 million bytes per second).

But just because the CONNECTION has that kind of capacity doesn't mean the drive itself is that fast. A typical 7200 rpm hard drive peaks out at around 120-150 MByte/sec no matter what kind of connection it uses.
April 29, 2010 6:08:32 AM

Thanks!

Well, that makes 3 or 6 kind of irrelevant doesn't it? They market things well I guess.
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a b G Storage
April 29, 2010 4:14:47 PM

The faster controllers will be more relevant when SSD technology becomes mainstream. SSD's are already approaching the limit of 3.0 Gb/s controllers. Conventional hard drives, as sminlal pointed out, are no where near the limits.
a c 415 G Storage
April 29, 2010 10:14:47 PM

Almost all current hard drives would work just as fast with SATA Revision 1 (150Gbits/sec). But some wouldn't, and SSDs would certainly suffer. SATA Revision 2 (300Gbits/sec) was developed a few years back to handle those higher-performance drives.

Today we have the fastest SSDs starting to exceed 300Gbits/sec, so SATA Revision 3 (600Gbits/sec) is being introduced.

The thing is that the IC and product manufacturers don't like having to work with multiple generations of chipsets - they'd much rather standardize everything around one set of support chips that implement the "current" version of the SATA standard. So soon you'll see all SATA products using the 6GBit/sec chips whether they actually need it or not.
April 29, 2010 10:53:57 PM

Thanks! I specifically asked because I saw a Western Digital Black drive that was 6 Gb/s. This was not a SSD, so I didn't even think most drives would get 3.
April 30, 2010 12:26:03 AM

Yall got the idea down, but I just wanted to clear up the the numbers being misquoted here and there.

SATA I --> 1.5 Gb/s bandwidth --> 187.5 MB/s transfer
SATA II --> 3.0 Gb/s bandwidth --> 375 MB/s transfer
SATA III --> 6.0Gb/s bandwidth --> 750 MB/s transfer

Don't confuse bits and bytes. You're dealing with bytes when looking at actual transfer speeds. (TIP: Divide by 8 to convert bits-->bytes)
a c 415 G Storage
April 30, 2010 4:47:23 AM

andrewc513 said:
SATA I --> 1.5 Gb/s bandwidth --> 187.5 MB/s transfer
SATA II --> 3.0 Gb/s bandwidth --> 375 MB/s transfer
SATA III --> 6.0Gb/s bandwidth --> 750 MB/s transfer


SATA is a communications protocol and there is some overhead involved so you can't just divide by 8 in order to get the speeds. The actual peak burst speed of SATA I is almost exactly 150MBytes/sec (where 1MByte/sec = 1,000,000 Bytes/sec). Similarly SATA II is 300MByte/sec and SATA III is 600MByte/sec.

See: http://en.wikipedia.org/wiki/Sata
a b G Storage
April 30, 2010 8:04:43 AM

sminlal said:
SATA is a communications protocol and there is some overhead involved so you can't just divide by 8 in order to get the speeds. The actual peak burst speed of SATA I is almost exactly 150MBytes/sec (where 1MByte/sec = 1,000,000 Bytes/sec). Similarly SATA II is 300MByte/sec and SATA III is 600MByte/sec.

See: http://en.wikipedia.org/wiki/Sata


The overhead is due to the 8b/10b encoding, so you can actually just divide by 10 for the effective transfer rate. SATA 3.0Gbit can transfer 300 megabits per second.
April 30, 2010 8:06:46 PM

So here Gb/s really is Megabit per second or megabytes?

Either way, can the transfer rate really reach 300 megabits?
a c 415 G Storage
April 30, 2010 11:54:41 PM

A SATA Rev. 2 connection can transfer 300,000,000 bytes per second, but mechanical hard drives can't actually accept or deliver data that quickly for a sustained period.
May 2, 2010 4:40:04 PM

sminlal said:
SATA is a communications protocol and there is some overhead involved so you can't just divide by 8 in order to get the speeds. The actual peak burst speed of SATA I is almost exactly 150MBytes/sec (where 1MByte/sec = 1,000,000 Bytes/sec). Similarly SATA II is 300MByte/sec and SATA III is 600MByte/sec.

See: http://en.wikipedia.org/wiki/Sata


Of course, that's a given, just throwing the the theoretical maxes.
May 4, 2010 9:40:41 PM

Wow you all have some great answers. Though, I have another question, does this mean that 3.0 is inherently faster than 6.0. I assume this would depend on the motherboard as well.
a c 415 G Storage
May 5, 2010 12:12:17 AM

Both SATA Rev. 2 (300MByte/sec) and SATA Rev. 3 (600MByte/sec) will basically perform the same if the device itself has a maximum transfer rate less than about 300MByte/sec.

There may be differences in the chipsets or adapter cards, though. For example if you have a 2-port SATA Rev. 3 adapter card that connects via a PCIe 1X connector, the PCI connection is a potential bottleneck because it can't handle the full data rate from both SATA ports. But it would only be an issue if you have two devices connected to the ports which actually have an aggregate data rate faster then a single PCIe lane.
May 5, 2010 2:16:17 PM

No, the real issue is I purchased a HD and I found that I can get one cheaper so I can return it and get the other one. The only difference is that the one I currently have supposedly has a 6.0. The ones I would replace it with would be 3.0. I would be connecting the SATA as normal so it should all be fine in that respect.

Hope I am explaining that correctly.
a c 415 G Storage
May 5, 2010 6:12:26 PM

To state it one more time:

There's no difference in performance between a 6Gbit/sec hard drive and a 3GBit/sec hard drive if the data coming off of the platters doesn't exceed 3GBit/sec.

To the best of my knowledge there are no consumer hard drives made today that have transfer rates faster than 3GBit/sec. The fastest 2TB 7200RPM drives today only achieve a sustained transfer rate of around 140-150MByte/sec (less than 1.5Gbit/sec).

Any difference in performance between 3GBit/sec and 6GBit/sec hard drives is due to differences in the drives themselves, not due to the SATA connection. Make your choice based on the actual specifications of the drives, not what type of connection they have.
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