rxt@lanl-a.UUCP (06/15/84)
<> I am in the process of getting a DEC Rainbow 100+ computer. (I will not go into the trouble I am having!) Anyway, now I need some floppy disks. I was told by a friend of mine that single density disks are different, but all double density disk are the same. Thus, I do not need to buy quad density (which is what the Rainbow supposedly needs), but I can use double density. I bought a box of single-sided double-density disks when I was using a Rainbow before, and they all worked fine. Also, the company I was with issued double density disks, not quad density. Now I am thinging of using double sided disks, and modifying the disks so I can insert them backwards. I believe that I was told that single- sided disks are in fact double sided, and that they will work. Does anybody know the facts? Also, what brands are recommended and not recommended? Thanks in advance for any help that you can give. Richard Thomsen
emjhm@uokvax.UUCP (06/17/84)
#R:lanl-a:-910200:uokvax:3400044:000:2638 uokvax!emjhm Jun 17 12:53:00 1984 Double Density Single Sided disketts are manufactured form the same double sided oxide coated Mylar ribbon. Some manufacturers coat the oxide layer with a non abrasive lubricant to reduce head wear which is more critical on double sided (ie two heads) because of the hard surface on either side of the diskette. In other words, a DDSS diskette usually means that it has been lot screened and certified to have no dropouts on one side. It doesn't mean that the other side is not just as good but rather that it has not been certified. Of course the lot screening doesn't guarantee that the certified side is good either but the company that sells the didssketteses has guaranteed that if you find a bad one, you can get it replaced. Now as for making a flippy diskette. Most disketts are not really made properly to spin backwards. If you punch an index hole and write protect hole in the jacket so that you can put the disk in upside down and record on the other side of a singleon a single sided drive, this could cause the wiping action of the fabric inside the jacket to release some of the oxide that it has been cleaning from the diskette surface. When this happens, you take the chanced of getting some of this loose oxide picked up on the head and cuausing dirty heads which can destroy disketts and decrease the life of the heads. On a single sided drive, the soft pad opposite the disk head can also pick up some of the devrisbris and there is no effective way to clean it so you have to partially dismantle the drive and replace the pad if it gets dirty. If you use a diskette which has both sides poillished and coated with a silicone surface like scothScotch or Datalife Verbatim, you will probably have no problems. Even though it's probably not recommendsesd to use both sides of a diskette, most people who have sidngle sided drives punch the holes in the jacket and end up with twoice the capacity and have relatively few problems despite the analytical rpoblemsproblems mentioned. By the way, they used to manufacture foloppy disk drives which had two sets of photocells for the index and write rprotect sensors so that you could use both sides of a floppy diskette without punching the holes in the jackett I havent't heard of these kinds of drives mentioned for quite a qhilewhile. I'm not sure that it was because of problems like those mentioned before or that the extra expense could probably but you a double sided drive uy you a double sided drive in which case thae dual photocells were not needed. Hope this helps...
punia@uvm-gen.UUCP (David Punia) (06/21/84)
One thing to keep in mind regarding your Rainbow is that many SSDD diskettes may work (indeed, I have even had success with SSSD disks), but the diskette manufacturers certify their diskettes to certain performance levels. They all come from the same bin. Those that can't hack the required performance of a denser media are certified as SD. I wouldn't suggest punching extra holes in the diskette to use the second side for reasons cited in another reply (emjhm@uokvax). If you choose to use diskettes that the manufacturer will back up, you want SSDD and 96 TPI. Certain manufacturers claim to certify the entire surface of their media, in which case the 96 TPI clause could be ignored. Other SSDD media will only be certified for 40 or 48 TPI operation, so you take your chances. There may be bad areas between tracks that your rainbow will attempt to use. I have heard that there is public domain software that will check a diskette for bad sectors and set up a list for the operating system so as to avoid using these areas, but I have no detailed info on that. Hope you enjoy your Rainbow. Good Luck!