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What makes SDD drive faster than other Drives

Posted on 2014-07-25
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I know that SSD drives are faster than regular drives, but I am not sure what makes them faster.
I know that there is RAID 0 (Striped)used on the servers, that makes Writing faster(Not sure about reading if it is fast) however it requires at least two separate drives.

SSD I believe it is a single drive but fast. I need to understand what makes it faster.

Thanks
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Question by:jskfan
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by:Ken Butters
Ken Butters earned 250 total points
ID: 40219719
"Other drives" have a stack of platters that have to rotate to bring the data under a read/write head.  There is a lot of mechanical movement involved in read/write operations for standard drives.

SSD drives have no moving parts, in that regard, they are more similar to a thumbdrive than a traditional hard drive.
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by:Joe Winograd, EE MVE
ID: 40219725
It is faster because it is solid state memory, meaning there are no moving parts. A standard hard drive has rotating platters (typically at 5400 or 7200 RPM for PC drives) and a read/write head on an actuator arm. So it takes time for the rotating platter to reach the point where the data is that you're accessing and time for the actuator arm to move in and out to position the read/write head in the correct location for the data. None of this exists in SSDs — it is all just memory chips, so access time is essentially the same — and fast, if it's a good quality SSD. Of course, just as main memory (aka RAM - random access memory) access times can vary based on the speed of the memory, so, too, can SSDs have different speeds. A web search for SSD will give you plenty of info to study, and the Wikipedia article is a decent place to start:
http://en.wikipedia.org/wiki/Solid-state_drive

Regards, Joe
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garycase earned 250 total points
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Do you remember LP records?   A hard drive works like that.

To access a particular point (or song on a record), you have to move the head to the correct track (the arm/stylus assembly on a record);  then wait for the platter (disc or record) to rotate to the location where the data is (or the song starts).    THEN you can start transferring your data (listening to your song).

The time it takes to move the head to the correct cylinder is called see time, and is typically 8-12 ms on modern drives.    Then the time it has to wait for the disc to spin to where the data is is called rotational latency.   Together, the sum of seek time and latency is the "access time" -- typically 12-18 ms on modern drives.

AFTER that access time delay, the data actually starts transferring ... the rate of transfer depends on the areal density of the platter and the rotational speed of the disk, but on modern drives is generally 100-150MB/s.

An SSD has almost zero "access time" => it's not zero, because seeking and latency are replaced by the time for the addressing electronics to settle, but it's typically on the order of 50-100 us (less than 0.1ms ... compared to 12-18ms on rotating drives this is effectively zero).   Further, the transfer speed of an SSD is much faster than for rotating drives ... usually 300MB/s or faster.

By far the biggest reason SSDs "feel" so much faster is the effective elimination of access time.   The faster transfer speeds make little difference, since most transfers aren't large enough for that to be a big factor.   But the fact that the transfers can start almost immediately means many disk accesses are DONE on an SSD before they would even start on a rotating platter unit.
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by:jskfan
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Thank you Guys!
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by:Joe Winograd, EE MVE
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You're welcome. Happy to help. Regards, Joe
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