From example lets take this computer where in the spec it says

Hard Disk Drive Specifications:
SATA 3.0Gb/s

When looking at harddrives under RPM 7200 they say either 6.0Gb/s or nothing at all. Only when I go down to 5400/5900 does it say 3.0Gb/s. Does this mean my computer wont benefit from a fast harddrive? Does this mean SSD would be useless except for fast seek times?


Let define few things:

RPM: rotation per minute, higher is better. So 7200 is better than 5400. But the rotation speed doesn't indicate the transfer speed. The seek time is affect by the rpm

Sata 6.0Gb/s or 3.0Gb/s: 6.0Gb/s is in theory better, but hard drive can't reach those speed yet, so for now 3.0 or 6.0 are kind of equals

A HDD can offer a speed of about maximun 450Mb/s (depend on HDD and the tests, etc), but HDD have a latency while moving the head. SDD don't have a moving part, so it's can be quicker (fast seek time).

SDD are usually better than HDD, HDD are cheaper than SDD. You can forget the 3.0Gb/s or 6.0Gb/s for now except if you buy a high-end computer with SDD / RAID. But if it's the same price, and you will keep your computer for a long time, go with the 6.0Gb/s

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    The seek time is affect by the rpm - The RPM only affects rotational latency and total access time. Seek time is totally independent of RPM of the spindle. Your use of "transfer speed" is ambiguous; there are two discrete transfers during a HDD read (or write) operation: platter to sector buffer through R/W head, and then the SATA interface transfer. These are separate and sequential transfer operations. – sawdust Mar 22 '12 at 8:32
  • @sawdust you seem to know very well how all this concepts fit together, why don't you answer the question so that we can learn from what you know? Thank you! – davidag Nov 24 '12 at 11:59
  • @DavidA. - Perhaps you might find this interesting: superuser.com/questions/518870/is-7200rpm-thru-sata-2-worth-it/… – sawdust Dec 13 '12 at 21:40

Not sure I understand what you are asking.

As a general rule a faster hard drive with more throughput is better. You will get information quicker and things will load faster.

HDDs - reliable (within reason), good speed, cheap, plenty of space, but contain moving parts and consume more power.

SSDs - newer tech, more expensive, less capacity available, faster (generally speaking), lower power usage.

So it comes down to 3 things, how much storage do you need? how fast do you need it to be? and how much money are you willing to throw at it?

  • My question was about RPM and "SATA 3.0Gb/s". It sounded like any RPM>6k is too fast for "SATA 3.0Gb/s". But this confuses me, my laptop harddrive is 5400 and windows reported 10+gb/sec. I'm really confused for the moment. – user3109 Mar 22 '12 at 0:39
  • Thanks to the other answer I realize what i saw was 10/20 MB not GB per second. That was stupid of me. – user3109 Mar 22 '12 at 1:01

Unfortunately you will find that specification sheets are often mangled, usually in an attempt to simplify the specs to your average person.

However in this case, on the link you provide, the full line what you are refering to is actually this:

Interface   SATA 3.0Gb/s

So that means the interface is rated to support a speed up to 3.0Gbits/sec - this would be a SATA-II interface.

No spinning hard drive will approach 3.0Gbits/sec except when it is transferring data from its buffer - buffers on hard drives are pretty small compared to the storage on the drive so it's usually not something that would be a dealbreaker. The speed benefit between 3.0Gbits/sec and 6.0Gbits/sec (SATA-III) is minimal for spinning hard drive.

Some solid state drives will break the 3.0Gbits/sec barrier and those can benefit.

An SSD that can transfer at 6.0Gbits/sec rate will still be much faster than a spinning drive on a 3.0Gbits/sec interface.

You have to read the specifications on the hard drive and see what its maximum transfer rate (for both read and write) is to determine whether it can take advantage of 3.0Gbit/sec or higher.

  • ah ha thanks. That clears a lot up. I'm thinking about getting tigerdirect.ca/applications/SearchTools/… which is 6gb/s. If the buffer is 64mb I'm a little unsure how it can break 3gb/s? I guess the speed doesnt matter and i should just get a good drive. I'm a little unsure how RPMS and cache affects it. I dont suppose it can do 64mb per rotate which is 7k per second? – user3109 Mar 22 '12 at 1:15
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    The buffer is just a bit of RAM acting as a cache - the drive will try to satisfy read requests from buffer RAM when possible and fill its buffer RAM in anticipation - RPMs affect seek time - The days when you could even find out how many sectors per track, cylinders, etc. are long gone; it's all just a bunch of LBAs now. – LawrenceC Mar 22 '12 at 1:55
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    No spinning hard drive will approach 3.0Gbits/sec except when it is transferring data from its buffer Actually all command and data will be transferred at full SATA interface speed. The sector data is always to or from a buffer, either the cache or the sector buffer. You are repeating a wide-spread misconception. Also, RPM only affects rotational latency, not the seek time. – sawdust Mar 22 '12 at 8:21

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