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Average seek/access time of a flash memory drive

Posted on 2004-09-19
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Last Modified: 2010-04-03
Hi Experts,

How do I know the "average access/seek time" of a flash memory drive? Is there any website that I can download the datasheet of a flash memory? I surfed around and all I got is read/write time. Is the read time = average seek time?
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Question by:icysmarty
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9 Comments
 
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Expert Comment

by:nobus
ID: 12094481
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Author Comment

by:icysmarty
ID: 12094494
I can't find the datasheet for "DiskOnKey", and it doesn't say anything about average seek time though.
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LVL 92

Expert Comment

by:nobus
ID: 12094523
well there is no such thing basically; the term average access = the time it needs in average to access the data on a HDD, the seek time is the time the arm with the head takes as an average to position correctly on the data. Flash drives are Memory units, they don't have heads to be positioned.

This clear enough?
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Author Comment

by:icysmarty
ID: 12094539
For a flash memory, we should say average access time instead of average seek time? I guess.
So, average access time = time it takes to read the data?
I need to download a Datasheet of a flash drive to look into it. Have searched several website, and most of the information they provided is about read/write time. So, I guess that's pretty much about it?
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by:nobus
ID: 12094559
Yes, they give the data throughput rate, which is more or less the transfer speed, and that is the only figures they have: read speed and write speed
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Author Comment

by:icysmarty
ID: 12094564
Do they have a datasheet?
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Accepted Solution

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cyrnel earned 50 total points
ID: 12094778
Icysmarty, "average access" is a real spec separate from seek. It's traditionally meant to include the time required for an average seek plus a half rotation of the platter. Even when on the correct track the head will have to wait for the platter to rotate until the desired sector is underneath. Average Access = seek plus this latency.

Flash RAM has none of this latency or seek time. The data are available, waiting for the controller to register an address and strobe for access. Even if you count it, essentially the same activity is required before a hard drive begins to perform an access. A pen-drive with USB interface does have negligible overhead, in the form of commands sent serially, but even low-speed USB (1.5Mb/s) can move a page of text in 8ms. That's a lot of memory requests. Since access is essentially zero, more important is how quickly data moves between the flash memory and its destination. Variables will be the type of flash RAM and the interface (USB type or IDE or PCI or...) and the bandwidth available after other devices have used their portion.

Finally, don't put too much faith in datasheets. They're good for a first take but don't hang your job/grade/wealth on them without testing to verify for your application.

Dave
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Author Comment

by:icysmarty
ID: 12096278
Thank you, I got it.
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LVL 92

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by:nobus
ID: 12099712
Nice , i give you 3 answers, and finally you give the points to someone who repeats what i say !
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