Let's briefly talk about magnetic tape, which is usuallyused for backup purposes or so-called secondary storage, whichmeans that the magnetic tape is not the firstdevice on which you look for your data.
You firsttry to find your data on the hard drive.
And only if it's not there, you go tosecondary storage.
Either because the hard drive was lostand you need to restore and back-up or because thisdata was not used for a long, long time, so it was stored on tapes and put awaysomewhere.
Tapes can have large capacity and are usuallyreplaceable.
Meaning you just bring a reel of tape andyou attach to the tape machine.
But their accessis fundamentally sequential.
We need to seek along the tapeuntil we find the point we are interested in.
So tapes are very good for things like back-up restoringback-ups and so on when you're writing things sequentiallyfor a long time or reading them sequentially fora long time.
But tapes are not very good,for example, as a virtual memory or something like that.
Tapes are slowly dying out, mainly because they havea low production volume because not many people actually usetape.
So the cost of tapes is not droppingas rapidly as the cost of disks, which have muchmore mass production, so their cost gets cheaper overtime.
And at this point, it's cheaper to buyan entire hard drive together with all the motorsand the head assembly and a built-in electronics forit, than to buy some tape and the machinethat will read it.
So people for example, useUSB drives which is pretty much an entire harddisk just packaged with a USB interface, as a methodof backup storage and so on.