vanam@pttesac.UUCP (Marnix van Ammers) (07/19/86)
Mybrother, who has a MAC+, says that he uses single sided disks and he only gets a bad one out of every 10 that he tries. Since single sided disks are typically 15 to 25% cheaper, it might be worth it to buy them for non-critical applications. I've heard that single sided disks were originally made to be double sided but that the manufacturer's tests found one side to be bad and so sell them as single sided. Can anyone confirm this? Marnix --
hull@hao.UUCP (07/19/86)
The situation you cite is only one of many possible scenarios. There are
several contributors to the cost of disk manufacturing, and the media may
be less expensive than test equipment and test time. Some manufacturers
try to save money on the quantity of plastic used to make the case. This
can result in admission of a greater quantity of dust through a poor fit
half-to-half. Keeping in mind that there is a large unsealed gap at the
drive spindle in almost all disks, gaps around the edges may be critical
only in certain environments where the edges are more exposed to dust and
moisture than the sides.
So as it is, some manufacturers use the same process for both sides and
only format one side for test. You have a high probability of getting a
good double sided disk at single sided disk prices.
Others process both sides to the point they are assured that the unused
side will not damage a two-head drive, polish the good side, then test.
The amount of polish on the unused side then can vary from so little that
loose oxide will foul your head to the point you will need to clean it,
to a situation in which the disk will appear to read and write ok when
new, but then begins to "forget" data not re-written frequently (as loose
bits of oxide containing information are rubbed away). You can inspect
new disks visually by opening the trap door and examining the image of
a bright object with sharp edges (a light bulb at a distance of 10 feet
will do) reflected off the surface. Compare the two sides. Remember to
look at the surface as though it was the mirror of a cosmetic compact
(gawd, am I so old that I have to explain what that is?), concentrating
on the appearance of the far object rather than the surface itself.
Minor distortion of the image is not a problem; however, a cloudy, fuzzy,
or indistinct image is an indication of an incomplete polish. To get an
idea of what's tolerable, inspect a known reliable disk you've used for
a while (a Workbench disk, for instance). Don't breathe on the disk; be
careful not to get eyelashes, nose hairs, bougars, or spit balls in the
open trap door ;-)
Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
...Then only the deranged will discuss yet unproven concepts]
{ucbvax!hplabs | decvax!noao | mcvax!seismo | ihnp4!seismo} !hao!hullkurt@fluke.UUCP (Kurt Guntheroth) (07/22/86)
Single sided disks ARE usually double sided disks that have failed an inspection on one surface. This is a true fact. Your friend with a MAC has only DETECTED one bad disk out of 10. Possible explanations: (1) The bad spot happens to be in an intersector gap. (2) the bad spot is on an inner or outer track the MAC doesn't use. Or most hideously (3) Your friend happened to write a best-case set of bits onto the bad spot so it worked, or the MAC doesn't check things too well until it actually writes to a sector. The "use single sided floppies" idea has come up over and over again. Most times it lasts awhile and goes away, as people chalk up disk errors that trash their work or toys. If you had an Apple-II or C-64 which wrote big fat lazy bits on the disk, you might get away with it, but you have an Amiga and are trying to get 800K on a disk. My personal advice is, unless you have the patience to reconstruct a blown file system by hand (ugh!), or don't mind trashing the odd disk, the 10% is not that much extra to pay for double sided disks. PS: I even had a double sided disk crap out on me once.
tainter@ihlpg.UUCP (Tainter) (07/25/86)
> Single sided disks ARE usually double sided disks that have failed an > inspection on one surface. This is a true fact. ^this is redundant^ This is almost right. Many single sided floppies are failures in double sided testing, but MOST of them have never been tested for double sided. The manufacturer needs too large a volumn of single siders to only ship those which fail double sided testing. --j.a.tainter
chiu@princeton.UUCP (Kenneth Chiu) (07/26/86)
In article <2261@ihlpg.UUCP> tainter@ihlpg.UUCP (Tainter) writes: >> inspection on one surface. This is a true fact. > ^this is redundant^ I thought a fact could be true or false. For example, "The sun rises in the west" is a false fact. -- Kenneth Chiu UUCP: princeton!chiu Princeton University Computer Science Department BITNET: 6031801@PUCC
gary@mit-eddie.MIT.EDU (Gary Samad) (08/03/86)
In article <252@pttesac.UUCP>, vanam@pttesac.UUCP writes: > Mybrother, who has a MAC+, says that he uses > single sided disks and he only gets a bad one out of every > 10 that he tries. Since single sided disks are typically > 15 to 25% cheaper, it might be worth it to buy them for > non-critical applications. I've heard that single sided > disks were originally made to be double sided but that > the manufacturer's tests found one side to be bad and so > sell them as single sided. Can anyone confirm this? Yes, that is what manufacturers often do, although I have heard of manufacturers sometimes selling double sided disks as single sided ones because of oversupplies of double sided*! disks. Now, as far as using single sided disks as double sided, I NEVER do this because of the major hassle of reconstructing a bad disk and because I don't like unnecessary worry. Also, think about what you are REALLY saving...15 to 25% cheaper minus the 1 bad disk in 10...that makes them 5 to 15% cheaper...Is it really worth the worry? Gary