I have heard someone saying that someone else said hard-disks need to be "moved" once in a while meaning it has to spin or data has to read or written to once in a while or something like that.
That is true of most RAM, but no, it is not true of hard-drives.
(S)DRAM is volatile memory which must have the data re-written to it regularly to avoid it “fading”. There are non-volatile types of RAM which are used for things like the BIOS and video-game saves, but the kind used for the “memory” of a computer is volatile.
Another source of confusion might be that data stored on tape does indeed tend to “fade” over time. Because the tape is thin and spooled, the layers of tape contain a small magnetic field in such close proximity to each other, they will eventually cause degradation, so reading the tape before it degrades and writing it back is indeed necessary to avoid data loss.
I am thinking about a external harddisk just as backup, and I will probably only move data on there every 6 month or so. The other time it will sitting in a "save place" somewhere powered off. I guess thats perfectly fine.
Why yes, yes it is.
I could image this somehow to be true since there is something with magnetic force going on inside ... and that some persistent conditions might be bad for it, that the data might "fade" or something.
Not quite. While it is true that hard-drives use magnets, they actually contain a “super” neodymium magnet which is used to control the read head. This magnet is quite strong and rests very close to the platters, yet does not wipe out the disk, so you can rest assured that any magnetic field from outside the drive won’t have much (immediate) effect.
But just assuming I would never use the Disk in 2 Years is it bad for it to never used in all that time? Or is this just a Myth? Will its live expectancy actually be better that way or worse?
The data won’t “fade” (at least not after only two years), but depending on the environment you store it in, other problems could arise. For one thing, you don't want to let it be too humid (which is why manufacturers specifically store and ship them with packets of desiccant).
And I by the way know that Hard-disks are not the Professional way for long time backup. So please stay on topic.
Why not? They hold up sufficiently well and are sufficiently cheap that they actually are a good general-purpose backup. Professionals with super-important data might use higher-quality drives, but there is nothing wrong with keeping an extra copy on a hard-drive. In fact, storage of all kinds is usually cheap enough that you can keep a copy on a hard-drive, flash-drive, memory-card, and even tape. That way you will maximize the chances of retaining at least one good copy of any given file.
With "magnetic force in there" I meant exactly what you are talking about. So this magnetic charge might go away after 10 years you say. So if I take that drive for a run after 9 years this magnetic charges not get renewed? Do I actually need to rewrite the data to make that happen? Or you mean that the disk will maybe lose its data after 10 years either way its its running daily or never ran at all? – Wayne's World 5 mins ago
Yes absent a strong external magnetic field, it will usually degrade over a few decades, but that is well past the expected lifetime of most drives anyway. They used to have lifetime warranties, then five years, then three. They get shorter and shorter and will likely die of other causes long before the data degrades.
