SDHC cards - lifetime ?
 

As the price drops. I must say that I am considering the SDHC cards as a storing media. The price for 1 hour HD recordings stored on a SDHC card is now almost the same as stored on a tape. Right now I am storing on harddrives but they will not work forever.
How long will a SDHC card remember the data on it. Is there any limit.

There was a proposed class of SDHC card called 'WORM' (Write Once Read Many) which would have a minimum of 100 years, at a cost way below that of standard SDHC cards. However, the price of a 16 GB card has dropped so thoroughly that perhaps there's less desire on the part of manufacturers and retailers to make that happen.

SanDisk mentioned back in 2003 '2 million hours MTBF', which if we assume 24/7 use, still works out at 228 years. Anyhoo - I can attest to having had cards go through washing machines (don't ask) without problems.

But that may assume a write and a read to/from the card every day for those 228 years, and that may well be fine, but it's a different case to writing once to a card and then being able to read the same data off it in the future. The data is stored as packets of electrical charge within an insulator, and EVENTUALLY that charge will leak away over time.

How long? "Many years" seems to be the best I've been able to find, and experience seems to suggest that data on cards is still fine after at least 5-10 years, how much longer than that you can expect is the big question.

The WORM technology I alluded to, and if I remember correctly, the memory one could get for Psions a while back, worked on the principle that the data space was switchable when current was passing through. When the current wasn't flowing, the data space 'crystallised' (not literally!) into an unchangeable state, hence preserving the data without charge, to all intents and purposes, indefinitely.

I will not pretend to even remember trying to understand the exact science of this, but I still have my documents from my Psion 3 and 5, but I have no functioning hard disks from that era...

The issues that people were worried about then was not about longevity, but (again IIRC) the wearing out of the ability to go from writeable to fixed state and back. For our purposes, that isn't a problem but of course it is if you're packing out SSDs as a boot volume).

Yet the biggest issue I've experienced is that a lot of the data I kept from 1988 onwards (via CD-ROM at £100 per disk in 1992) isn't usable because the file formats are out of date - though QuickTimes, MPEGs and JPEGs still work!

Yes, what I said was in reference to standard flash memory, not WORM. This was discussed in another thread a couple of weeks ago - http://www.dvinfo.net/conf/sony-xdca...ability-2.html - and it's worth reading the Wikipedia reference I quoted then. (Post #16, references to Sandisk WORM post # 21.)

The Sandisk WORM memory is called 3D, and details are sketchy, but it seems likely that it's not suitable for what we might want it for. (Recording video in a camera and long term storage.) It seems likely that current SDHC devices will be compatible with it as far as reading, but not necessarily writing.

Perhaps not as an in-camera recording medium, but the promised cards (due out in 09) will certainly provide a more than viable storage medium.

I really hope you're right, but before too many hopes are raised, the Sandisk site says about them:
which leads me to believe that they may need factory equipment to do the writing, and realistically we're talking about a process more like DVD replication. That's fine if you want to send out 10,000 copies of new mapping data to satnav users, not so good for people on these boards.

David, that reference has nothing to do with the new cards due out later this year.

Provided they are kept in a cool, dry place I'd expect most SDHC cards' lifetimes to outlast our own lifetimes...

Noah

The SD card memory charge should stay until until the insulator breaks down. Were not talking thousands of volts, just a couple of volts so they should last many years. probably as long or longer than a burnt CD or DVD which have dyes that do deteriorate with age and probably longer than a hard drive that has bearings that either wear out or seize up.

Do you have any references about that, Jay?

My interest is not just academic, because a WORM SDHC card that a camera like the EX could write directly to, with a manufacturers quoted lifetime of 100+ years would be little short of the Holy Grail for an archival project I'm working on. All I've been able to find officially is what I quoted, but I'd love to be proved wrong.

And does anybody know of any solid references about how long data may last on a standard card? Again, recording directly to card and archiving that is exactly what I want to propose, but the end-client will need to be satisfied it will have a long lifespan. And by satisfied, they will need science, not optimism.

Only what the Product Marketing Manager from SanDisk told me.

Do a "search this forum" for "WORM" and you'll find the thread.

OK, found that and I gather what you're referring to is:
Have to say I was hoping for something far more specific. I may be pleasantly surprised, but in the absence of any other hard facts I'm not holding my breath.

Hard to give specifics on materials that haven't been released yet.

Heaven forbid. We don't want anyone around here passing out!

While the data on the card may last many years, the usable lifespan of it may come down more to the mechanical connection / format. Remember those old 8" floppies? Very rare to even see one of those now, let alone one that works.

But I would put my money on a solid state memory card like SDHC any day over pretty much any other storage format.