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Are "1TB" micro-SD cards 1000GB or 1024GB?

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speachy:

--- Quote from: Frankenpod on May 20, 2025, 05:52:34 PM ---Thanks for that information.  So the issue is more likely to be just cards not being quite the capacity they claim to be, even if they are in theory using SI units?  I don't really know anything about the topic of memory-card-manufacturing, is there a degree of random variation in exact sizing? (leaving aside the issue of outright fakes).  Seems as if somehow the cards in this instance were a tiny bit _larger_ than claimed.

--- End quote ---

While the physical flash chips _probably_ have a power-of-2 array of individual cells, that's the _raw_ size.  Some of that space ends up getting used for other purposes than storing user data -- eg ever-increasing amounts of error correction, the flash translation layer (maps a logical sector to a physical one, eg for wear leveling and improved write speeds), and even the runtime firmware for the flash controller itself.   This overhead is fixed for a given design.

Then consider manufacturing testing. If you find a defective block, instead of scrapping the part you could just permanently mark it as bad in the FTL so it never gets used.  How much gets marked off depends on the individual part, but as long as you're still above your target capacity, great!  Otherwise you could just mark off a bunch of "good" sectors and sell it as the next-sized lower-sized part (eg 500GB instead of 1TB). This practice is called "binning"

What's left after all of that overhead and binning is the capacity that gets reported to the outside.

Frankenpod:
I admit this is increasingly not a Rockbox-specific topic.  But how 'smart' are SD cards?  Will they gradually reduce in capacity as sectors get marked 'bad'?  I was under the impression that SD cards are significantly 'dumber' than CF cards with regard to that sort-of-thing.  Just am puzzled why I end up with such different total capacity with combinations of what are nominally the same capacity cards (which makes it tricky to get as close as possible to the 2TiB limit without going over it).

gevaerts:
I suspect SD cards *used* to be dumber than CF cards, but I also suspect that that was a matter of having the space (and heat capacity) for a fancy controller. These days everything is smaller and less power hungry, so I don't think there's a real reason to not have similar fancy logic in an SD card, at least a higher end more expensive one.

I'm speculating though

saratoga:

--- Quote from: Frankenpod on May 22, 2025, 07:39:13 AM ---I admit this is increasingly not a Rockbox-specific topic.  But how 'smart' are SD cards?  Will they gradually reduce in capacity as sectors get marked 'bad'?  I was under the impression that SD cards are significantly 'dumber' than CF cards with regard to that sort-of-thing.  Just am puzzled why I end up with such different total capacity with combinations of what are nominally the same capacity cards (which makes it tricky to get as close as possible to the 2TiB limit without going over it).

--- End quote ---

They do at least some wear leveling so you shouldn't have loss of capacity until essentially the whole array is finished and the controller can't find any remaining good block to map to a new write request.  I think at that point they stop working or go read only.

Frankenpod:
Having had a reason to re-open some ipods, I checked the individual cards from it in a card reader, and it it seems that Sandisk "512GB" cards are reported as 477GiB (which is what I'd expect from a simple math conversion, i.e. a factor of (1000/1024)^3 ) while Integral "512GB" cards come out as 461GiB.  Got the same figures for a few cards of each type.  Not really making any point or asking about it, just putting the information out there if anyone finds it useful to know.  Am now curious to find what other brands/capacities come out as.

Edit - needed to open another one, and again, the Integral was 461GiB and the Sandisk Ultra is 477.  Seems clear Integral are not quite the capacity of Sandisk.  The small differences aren't a big deal (I wouldn't shun Integral cards for the sake of that 16GiB).  The only thing is, it seems, the variation can make the difference as to whether you go over 2TiB (causing complete failure!) or not.

Have Samsung, Patriot, and Amazon Basics cards in other ipods, but haven't had any reason to open them up.  The one with Patriot cards in it seems suspiciously on the low side, so maybe those are like the Integral ones, a little smaller than the norm?

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