RichC
Well-known
Ronald's right, despite protestations from others!SD cards fail after 7 years.
Solid state "flash" memory devices can be used for decades, and unused perhaps last a century. However, they're not designed for long-term storage, as the stored data "pattern" degrades over time. Manufacturers of USB drives, SD cards and the like suggest long-term storage to remain viable for about 5 years. So, we can expect our stored photos on SD cards to start failing between 5 and 10 years. That's an average, so Joe Bloggs saying his card's lasted 15 years is of no consequence.
The most archival way of storing electronic data is on optical discs - just as it has been for ages. Archival "gold" DVDs, for example, should last at least a century - and they're cheap, easy to create and convenient to store. Owing to their convenience and reliability, DVDs should be around for a few more decades yet (despite Apple's attempts to kill off optical drives!).
Blu-ray can store 10 times more data on a disk, which have been suggested may last 1000 years! However, DVD is a far more established technology: so there's the concern that in the future you will still find DVD drives while Blu-ray drives have disappeared through obsolescence.