SLC vs. MLC, MMC vs. SD

[Alan Dayley]

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der.hans wrote:
> moin, moin,
> 
> "Description: Ultra Performance 80X Secure Digital cardsis the best choice
> for your digital cameras and other handheld device. Different from other
> manufacture, Transcend insists on using only original SLC
> (Single-Level-Cell) NAND Flash chips that have a higher write speed, lower
> power consumption, and superior durability compared with Secure Digital
> cards made with MLC (Multi-Level-Cell) chips."

Single level cell = 1 bit stored in each flash cell
Multi-level cell = 2 bit stored in each flash cell

MLC means you get double the storage capacity in the same amount of
silicon.  Makes for cheaper manufacturing and, therefore, less expensive
per byte for the consumer.

However, the above description in my experience is correct, MLC is not
as durable as SLC.  Adtron *only* uses SLC.  No MLC flash has ever
passed our tests, not even close.

On the other hand, MLC in a consumer device, in normal consumer uses
will probably be just fine.  Just stick with a known memory manufacturer
(SimpleTech, Kingston, SanDisk, for examples) rather than no-name brands
and you should be fine.

> Is that marketing drivel or does it really make a difference? I haven't
> noticed quick with the transcend card for my phone, but that's probably
> more due to the phone and Verizon sucking.

Speed may or may not be effected by MLC vs. SLC.  Just go with the card
rating understanding that the published numbers will be the burst
(short, quick transfer) rate under ideal conditions.  Expect to get
average operating speed at about half the published numbers.

> Can MMC and SD cards be used somewhat interchangably and you just lose the
> encryption option of SD?

Yes.  If a device can use SD an MMC will work in that device.  Not the
other way around, however.

Alan
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