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SSD is 256 gb but only showing 238 gb?

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  • SSD
  • Storage
  • Hard Drives
Last response: in Storage
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October 10, 2014 8:22:50 PM

Hello, i just bought a SSD 850 pro 256 gb and installed my OS, when i looked at the hard drive it said there was a total of 238 gb data? I thought it should be 256? Is this an error?

More about : ssd 256 showing 238

October 10, 2014 8:26:45 PM

It's something called "Over Provisioning" It uses 10% of space to move data around/to degrade the ssd equally over all the components within it.

Here's what it is in depth,

"An SSD controller is responsible for the massive task of managing all data traffic and storage for the drive. NAND technology’s intrinsic complexities require a lot of extra work behind the scenes. A data write is not as simple as placing data into an empty memory bank. Each NAND cell has a limited lifespan – it can only endure a specific number of data reads/writes. An additional layer of complexity is added by the fact that overwriting old data on NAND requires an erase of the entire NAND block (this same block may contain other data that is still valid). As a result, the controller is constantly moving data around to ensure that the cells wear evenly and to preemptively prepare “free blocks” to use for future data writes.
All of this management work requires the SSD to have a kind of “swap space” available to use as temporary storage while the controller goes about its business. The controller will use any available free space for this, but free space becomes a premium commodity as we fill our drives with data. OP is a way to set aside a minimum amount of free space, inaccessible to the user or the OS, which the SSD controller can utilize as a kind of “work bench.”

If you want more information you can read up on it here, http://www.samsung.com/global/business/semiconductor/mi...
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October 10, 2014 8:33:38 PM

Hi, although rmark's explanation is correct as far as over provisioning it has little to do with the usable size of the drive. The over provisioning for SSD is pretty much invisible to the end user.

What you are actually seeing is detailed here, http://www.tweakandtrick.com/2013/07/lost-storage-space...

Marketing is all it is.
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October 10, 2014 8:35:05 PM

Hard disk manufacturers calculate 1GB as 1,000,000,000 bytes. Microsoft calculates 1 Gigabyte as 1,073,741,824 bytes. This means you lose 7%. This is true of any drive and always has been. So a 120GB drive formats to 111GB, a 250GB drive gives you 232GB and so on. You can calculate exactly with this tool.

http://www.ussscctv.com/harddrivesizecapacitiescalculat...


It has nothing to do with over provisioning.
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October 10, 2014 8:36:07 PM

Thanks for the additionally information lucuis, I'm still learning here :) 
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