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Comment by allegory | Hacker News Reader

Try powering off for 5 years and keeping at 75oC and see if the data is still there.

Wouldn't most storage types, including regular hdds and optical media fail this test though? I am not talking about complete data loss, but some data would be corrupted after such time.

Decent quality hard disks and DLTs will probably be fine. I've had DLTs survive 100oC for over an hour inside a fire safe in a fire and some old Seagate Cheetah 10K U160 SCSI disks in an external SCSI case with a dead fan running at 80oC for a month quite happily. The latter was actually running and operational which is remarkable.

Some optical media will fail. It doesn't even have to be kept at 75oC from experience.

Flash will almost certainly fail (leakage increases with temperature). I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well...

These are all anecdotes, but there is data out there to support this as well.

"I've had dead CF cards, USB sticks, SD cards, the lot and corruption after only a couple of years stored in ideal conditions. Then there's the old Sun PROM crapfest to consider as well."

The story goes back much further with solid state if you talk to "retrocomputing enthusiasts" unfortunately eproms reading all 1 awhile is depressingly common. You only need a single bit error of course for software failure.

Another interesting point to bring up is it is Very well known in the retro community that the details of eprom programming technique and certification (or lack thereof) of eprom programers has a dramatic effect on burn lifetime, like multiple orders of magnitude difference in burn lifetime. Anyone can make an eprom burner that verifies an hour later. Much harder to make an eprom burner that verifies 10 years later.

This affects more than stereotypical retrocomputing due to embedded devices. Plenty of PBXes and machine tool controllers and scientific instruments and classic video arcade machines get scrapped because the eproms lost their minds.

Very good points there. I worked for an aerospace and defence company for a bit as an electrical engineer. Our software was always read into RAM, checksummed, the RAM was write protected via a register and only then the code was executed. The bootloader was a mask ROM. That was all just to work around the possibility of bit flips in EPROMs.

Magnetic media (hard drives, tape) will essentially retain data indefinitely unless exposed to magnetic fields that are strong enough or until the Curie point is reached, both of which are unlikely scenarios for long-term storage. Even in cases of fire that destroys the external components of an HDD, if the platters didn't get hot enough the data is still there:

http://istcolloq.gsfc.nasa.gov/fall2008/presentations/peders...

Flash-based memory is different - unlike magnetic media which can be thought to be bistable, flash is inherently unstable (monostable); the erased state of a cell is lower energy so the electrons stored in a programmed one are "under pressure", and due to tunneling effects, slowly leak out over time.

The consequence of this is that magnetic media will continue to store information long after it's obsolete; I'm almost willing to bet that the data on a modern HDD will still be there on the platters in 100+ years, even if the rest of the drive becomes inoperable. Ditto for optical media such as pressed CDs - in that case the bits are manifested physically, and unless the medium is degraded to the point where the bits are no longer distinguishable, the data stays (theoretically, even a CD whose reflective layer has degraded is still readable via SEM or other physical means, since the data is physically pressed into it.) On the other hand, flash will slowly and irreversibly erase itself over long periods of time, as each cell returns to its non-programmed stable state.

This is not exactly true, the magnetic fields on HDD migrate around on the disk over time and eventually become unreadable by the disk. In theory the data remains recoverable for significantly longer than that but it's not 'stable'. While historically not much of a problem it's a larger issue as HDD keep increasing in capacity.

HDD actually internally refresh data to avoid this issue so their much better as 'hot' storage. Tape is designed to avoid most of these issues and is much better for long term storage.

"Magnetic media – such as floppy disks and magnetic tapes – may experience data decay as bits lose their magnetic orientation. Periodic refreshing by rewriting the data can alleviate this problem. " http://en.wikipedia.org/wiki/Data_degradation

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