brown@CMU-CS-K.ARPA (Andy Brown) (07/11/85)
Whether it is a good idea to use both sides of a floppy disk depends
on two things:
1) Is the magnetic material on both sides of the disk error-free.
2) Are the disks designed to be "flipped". That is, can the disk
safely rotate in both directions with no damage.
Most floppy disks are manufactured with a magnetic coating on *both*
sides. The disks are then tested to make sure that there are no
defects which would make them unsuitable for data storage. If one
side of a disk is bad, then it is usually ceritfied as a single-sided
disk, if both sides are good, then it is certified as a double-sided
disk. When you buy blank disks, it will always say on the box whether
the disks are single or double sided. Therefore, most single-sided
disks have *known* defects on the uncertified side (you can tell which
side is the correct side because it has the label on it).
All floppy disks have what is known as a "liner". This is inside the
cover of the disk and it has two main functions: to minimize friction
as the disk is spinning; and to catch and redirect any dirt and dust
which may have found its way into the disk jacket. There are a wide
variety of liner designs, and some of them are intended for use with
disks that will only be spinning in *one* direction. Flipping a disk
with such a liner could cause dirt and dust that was trapped by the
liner to be released onto the disk, creating the potential for head or
disk damage.
It must be mentioned that there are really *two* kinds of double-sided
disks. Some disk drives, (such as the double sided drives in the IBM
PC) have two heads, one for each side of the disk. Thus they use both
sides of the disk, but the disks always spin in the same direction.
When you "flip" a disk on a single-sided disk drive, such as the
Commodore 1541, the disk will spin in the opposite direction when you
flip it. Thus there are some floppy-disks on which both sides can be
used, but you might not want to use the *back* side on your Commodore
1541 disk drive because using that side will cause the disk to spin in
the wrong direction.
It is absolutely safe to use both sides of a disk on a 1541 disk-drive
if the disks are certified double-sided on the box, and there is a
write-protect notch cut on both side edges of the disk. If not, then
it is risky to use the uncertified side for data storage.
If you buy a commercial software product which uses both sides of a
disk, then it is probably safe to assume that they are using the
correct kind of disk.
--- Andy Brown king@dciem.UUCP (Stephen King) (07/16/85)
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Another consideration is the index hole, which is not going to be in the same place if the disc is flipped over. Thus, the disc drive must be able to cope with the index hole on the other side of the disc center line, or discs with two center holes must be used. (has anyone ever seen any of these?) -Another note- the certified side of a disc is *not* the side with the label on it. When inserting a disc into a drive with the label up, the read/write head accesses the disc surface through the slot in the *underside* of the disc jacket. -=-=-= sjk
rbt@sftig.UUCP (R.Thomas) (07/16/85)
> > It is absolutely safe to use both sides of a disk on a 1541 disk-drive > if the disks are certified double-sided on the box, and there is a > write-protect notch cut on both side edges of the disk. If not, then > it is risky to use the uncertified side for data storage. > > If you buy a commercial software product which uses both sides of a > disk, then it is probably safe to assume that they are using the > correct kind of disk. > > > --- Andy Brown Interesting. I have *never* seen a disk with notches cut on both sides, except when I have personally known the person who cut them. Most 'double sided' software distribution disks I have seen have actually not had notches on *either* side. They must have been produced on duplicating machines that ignored the presence or absence of write protect notches. On the other hand, I have the following philosophy on 'flippy' disks -- Because of the dirt entrapment/releasing problem, it is never a good idea to use the 'back' side of a disk, unless the disk is (almost) brand new. That means that for day to day use, if you only have a single sided drive, you should only use the front side of your disks. Whether you buy disks marked 'single sided' or 'double sided' is a matter of personal preference, especially since the price difference is so small, nowadays. I buy 'double sided' disks, personally, because of the following observation -- There *is* one safe use for 'flippy' disks. That is for distributing software that is too big to fit on a single side. In that case, you are going to use a new -- fresh out of the box -- disk, so you are not worried about dirt, and the recipient is going to make a backup copy (onto *two* disks!) as soon as she gets it, then put it away and (hopefully) never have to read it again, so she is not worried about dirt either. I do enough software swapping that I find it useful to have a supply of 'double sided' disks readily available at all times. As an aside, I don't think it is possible to design a liner that will not entrap some dirt, and release it if the disk is spun the other way. That just seems like the the inevitable workings of the laws of physics to me. Enjoy! Rick Thomas ihnp4!attunix!rbt
jeffm@mmintl.UUCP (Jeffrey Miller) (07/22/85)
* Double sided disks are usually for drives with 2 heads. The disks still only spin in one direction. You still face the problem of releasing dirt trapped when spinning in the original direction. I've been using the flip side of single sided disks on a single head drive for several years with no problems on either side of the disk, even though it spins both ways. ************************************************* * Jeff Miller * * Multimate International Corp. * * 52 Oakland Avenue * * East Hartford, CT 06108-9911 * * UUCP: * * ...!seismo!utah-cs!utah-gr!pwa-b!mmintl!jeffm * *************************************************
hes@ecsvax.UUCP (Henry Schaffer) (07/24/85)
The people I know who use both sides of the disk in a single side drive (and call the disks "flippies") use a hole punch to punch the extra holes in the diskette jacket (*only*). --henry
Reno.wbst@XEROX.ARPA (Jim Reno) (07/29/85)
Back in 1975 or 76 when true double sided disks were just new I ordered some "two" sided disks and received what I didn't want. I got a disk with two cutouts for both index and write protect holes presumably certified for both sides. The one disturbing thing about a disk like this in my mind has to do with the purpose of the disk cover itself. If I am not mistaken considerable effort goes into the design of the cover to promote its ability to clean particles off the disk media. I believe this function is unidirectional and note that when flipped the disk will be spinning in the opposite direction with respect to the cover. Reno
ABN.ISCAMS@USC-ISID.ARPA (07/29/85)
Re using both sides .. I shall not address the safety of this, wear and tear, certified sides, etc. (That's been discussed plenty.) However, the index holes are no problem. I have a batch of junk disks I experiment with. THREE holes now! One at about 1:00 for single-side drives, one at about 2:00 for regular double side (yep, that's how the drive can tell!), and one at 11:00 for flipping single-sided ones. PS: you have to tape over the double-sided one if you want to do single-side or flip-side on a double-side drive! Gave me fits for a while. Regards, David Kirschbaum Toad Hall ABN.ISCAMS@USC-ISID
ABN.ISCAMS@USC-ISID.ARPA (07/30/85)
Return-Path: <info-cpm-request@AMSAA.ARPA> Redistributed: XeroxInfo-CPM^.wbst Received: from AMSAA (AMSAA.ARPA) by Xerox.ARPA ; 30 JUL 85 07:04:29 PDT Received: from usc-isid.arpa by AMSAA.ARPA id a007931; 29 Jul 85 8:27 EDT Message-ID: <[USC-ISID.ARPA]27-Jul-85 06:28:34.ABN.ISCAMS> Re using both sides .. I shall not address the safety of this, wear and tear, certified sides, etc. (That's been discussed plenty.) However, the index holes are no problem. I have a batch of junk disks I experiment with. THREE holes now! One at about 1:00 for single-side drives, one at about 2:00 for regular double side (yep, that's how the drive can tell!), and one at 11:00 for flipping single-sided ones. PS: you have to tape over the double-sided one if you want to do single-side or flip-side on a double-side drive! Gave me fits for a while. Regards, David Kirschbaum Toad Hall ABN.ISCAMS@USC-ISID
Burton.osbunorth@XEROX.ARPA (08/01/85)
Dave, I use an ordinary hole-punch to punch out the extra index holes. I use the jacket of a bad disk as a template. As a caution, the hole-punch could be magnetized, so disks should be formatted after this treatment. Use flippies only for archival disks, not work disks in a floppy-only system. Phil Burton burton.osbunorth@xerox