Magnets Vs. Tapes/Diskettes ?

Good question and I am curious to see the responses.

Don't know, but when you erase an audio tape, you are really just recording nothing. In other words, running it past a magnet. The only problem with placing them on a speaker magnet is that the erasure might not be complete, but making the new recording obliviates the old one anyway.

Interesting question. It is my understanding the magnetic sources you mention merely align the magnetic particles in such a manor as to render any info on said disks or tapes as undefined. Simply stated, any information previously recorded is no longer coherent and therefore useless.

I am not sure as to why you would add the extra step of erasing the media before recording on it. By recording over any info presently on any magnetic media one effectively erases while simultaneously recording the new information. However, I am not an expert in this area.

The above measures are unlike erasing files on a computer disk via the "Delete" command. The files so erased are essentially still on the disc and mostly intact. So with the aid of specific software one can recover all file information (The early versions of DOS/Windows contained a crude tool named "DEBUG" that allowed this). This is because of the way the operating system (i.e. Windows) handles files. DOS (Window's Grand-Mom) sets up a FAT table (File Allocation Table) where all the attributes of the file are stored. One of these attributes is the location of the beginning sector of the file in question. This "pointer" to the file's location is defined as "null" thereby telling the operating system, effectively, that that sector is free and can be overwritten by a "new" file. Quite elegant really, no matter how huge the "erased" file is the system need only change a couple of bites of info on the disk and need not waste time overwriting all the info in the file.

The format command of DOS/Windows may actually destroy said files, I am not sure. If the process includes checking for bad sectors it may very well destroy all the info. One way of checking involves writing a specific character to an area and then reading it back to see if it matches the original, this would destroy any original info previously on the disk.

Still remaining is the question of a really strong magnetic force such as that generated by, say, one of those that picks up wrecked cars. Would that permanently realign the media thereby destroying it's utility? Maybe it would suck the magnetic particles right off the tape/disc!

JM

We used to erase magnetic tapes, used for large amounts of computer data, by running them over a machine called a degausser that was basically a very powerful magnet.

The tapes could then be reused. The tapes actually worked better than those that were erased by the computer (on the tape machine).

I don't guarantee that magnets won't damage *any* magnetic media.

But I would be surprised if you would do any physical damage to a diskette video tape or cassette with a magnet.

It would interesting (and not that expensive) to experiement with a powerful magnet. Let us know the results.

With my limited knowledge, I suppose it would just align all of the info on the tape in the same direction. I haven't got a clue what that means though.

Could anyone explain how tapes work? And not just music or video tapes but (if anyone remembers these) those huge tapes for recording entire computer hard drives?

Is all of that just 0's and 1's?

Audio tapes are almost exclusively analog. Digital probably would have caught on quickly, but were made in such a way that professionally recorded tapes couldn't be copied. Guess what? Nobody bought them.

roger,

I rember the flap that was caused by the development of Digital audio tape. The recording industry gummed up the works for obvious reasons. Those efforts plus the passage of time allowed the new technology of CD's to race past and become perferred by audiophiles. Technology made and end run around the recording industry.

But the industry is back with a vengance.

Sheep:

The old tapes used to archive digital info were quite simple in principle. In conjunction with the computer operating system software the file information was stored a a series of dots and dashes (ones and zeroes) in the form of electronic pulses. Multiple files were placed sequentially on the tape using markers delimiting the beginning and EOF (End of File). High speed/density tapes are still being used today. These allow a lot of info to be cheaply "backed up" in case of hard disc corruption or distruction. Their efficient use otherwise is not even closely comparable to "Hard" drives (Old name: Winchester Drives). This is because, unlike a hard drive's direct access to specific records (files), tape storage demands a sequential read to access a file's content. If you want to read the last field of the last record of the last file you must go thru the entire tape to get to the info desired.

Analog tapes that record visual and/or audio information are much more complicated. This goes even for those of a digital nature. One must include not only different tracks (left and right sound channels) but also various other attributes such as sound frequency, volume, color, and briteness. Perhaps you might find a site that explains how this is done on, say, a VHS video tape. If so please share it with us. God is in the details!

JM

No a strong magnet will not erase the tape but it will destroy the magnetized portion and the tape will be unuasable. To erase the tape a demagnetizer should be used. This is a strong magnet that is plugged in to a AC outlet. The AC causes the magnetic field to keep reversing 60 times a second and a tape may be erased by holding it against the demagnetized and slowaly moving it away to reduce the amplitude of the field.

Also tape recorders have a erase head that erases the tape before it is rerecorded.

The basic principle is the same regardless of the type of magnetic media. The media is iron oxide (usually) embedded into some sort of backing. and the "information" is stored by magnetizing the iron oxide particles embedded in the media backing. As long as you can reverse the method used to record the media you can read it.

Passing the media across a strong magnet just realigns the polarity of the iron oxide particles so It won't physically destroy the media. It just removes any/all formating and information stored. As ebrown_p said, this used to be done all the time and you can still buy "bulk erasers" to do the job.

Early magnetic media (i.e. Open reel audio tapes, cassettes, 8-tracks, early Computer Tapes, etc..) used "Longitudnal Scan Recording" where a number of tracks were laid out parallel with the tape itself. Newer technologies (the VCR, DAT Tapes, etc..) used a "Helical Scan" where the information is recorded in short bursts that are laid out at a 45 degree angle across the face of the tape. Helical scan allows you to store more "tacks" of information in the same space compared to the Longitudinal scan so you can fit more info on the tape.

In the past they made coils of wire that were energized by 60 hertz power from the electric company for bulk erasing of magnetic media. I think results are good as new if you energize the coil several feet = one meter from the media; bring it as close as possible in a slowly rotating motion and withdraw (still rotating slowly)it slowly at least 7 feet = 2 meters before turning off the alternating magnetic field. It might be still better if a second person rotated the magnetic media as you separated the media from the deguaser. Using a permanent magnet can leave a bit of the old recording and reduce the quality of future recordings with that media, but typically the loss of quality is small. Neil