Reiability of wrong media (was: is out of 5-1/4" diskettes

From: Don Maslin <donm_at_cts.com>
Date: Thu Jan 21 17:15:46 1999

On Thu, 21 Jan 1999, Tony Duell wrote:

> >
> > [I am using the popular names (such as "360K", rather than more
> > technically correct designations.]
> >
> > The most important parameter is the magnetic coercivity.
> >
> > "360K" is 300 Oerstedt.
> > "1.2M" is 600 Oerstedt. Therefore, the two will not interchange
>
> Sure. Some of the IBM Techrefs get this wrong, BTW. At least one edition
> gives the same coercivity for the 2 types of disk.
>
> > satisfactorily. Unlabeled disks can sometimes be differentiated by
> > color. If a disk has a reinforcer around the center hub, then it is
> > probably a 360K, although it COULD be an after-market reinforcer (jigs
> > used to be available.) If there is NOT a reinforcer, then it is either a
> > 1.2M, or a very early "360K"
>
> Don't forget that '720K' 5.25" disks also exist, although they're not
> common on IBM PCs. By that I mean 80 track, double density, double sided,
> 300 oersted coercivity. Most of those do not have the reinforcing ring IIRC.
>
> > <RANT> There ain't no sech thing as a 1.44M disk. The IBM style of HD 3.5
>
> Agreed. But I've got fed up with people correcting me when I call them
> 1.4Mbyte disks and have adopted popular usage :-(
>
> > has 2 sides, 80 tracks per side, 18 sectors per track, and 512 bytes per
> > sector. If you multiply that out, you get 1.406 HONEST Megabytes
> > (1048576). The only way to get 1.44 out of that is to creatively redefine
> > a Megabyte to be 1024000 bytes. That leaves IBM in the position of
>
> 1440Kbytes is OK, though :-)
>
> 1 Megabyte is often defined as 10^6 bytes by hard disk manufacturers.
> Alas that doesnt' work for floppy disks either.
>
>
> > DS v SS (5.25"): The disks are manufactured the same, but the difference
> > is whether BOTH sides are tested and/or "certified". Using DS for SS is
> > acceptable. Using SS for DS is taking a chance on using untested media.
>
> Sure. But I have _never_ had a problem with using an RX50 as double
> sided, unlike attempting to use '360K' disks as 80 track ones, or even
> trying to format some lesser brands of disks as even 360K.
>
> I would not suggest using an RX50 like this for data that really matters
> (in fact I'd not keep that sort of data on any floppy disk apart from
> perhaps an 8" one). But if you need a few disks for a TRS-80 or BBC micro
> with 80 track drives then this is a possible solution. It works a lot
> better than using '360K' disks, even good name-brand ones.
>
> > "Flippy": The second side can often be used in a single sided drive by
> > flipping the disk over. In the case of Apple ][ and Commodore, it
> > requires punching a write enable notch. (Which does NOT need to be square.)
> > On TRS-80, IBM, etc, it is necessary to also punch an additional
> > (symmetric) access hole for the index hole. (jigs for marking and
> > punching used to be available.)
>
> THe Siemens drives in my Zenith Z90 have mounting holes in the chassis
> and pins on the PCB to connect a second index sensor and WP sensor. So
> you can use any disk as a flippy in those. My drives don't have the extra
> sensors fitted, though.
>
> >
> >
> > DS V SS (8"): The index hole opening is in a different location.
> > Punching a new hole through the jacket normally works OK.
>
> Be careful if doing this to turn an SS disk into a DS one. Double sided 8"
> drives have 2 index sensors so they can tell what sort of disk is
> inserted (there is a 2-side line on the SA850 interface). Some drives get
> _very_ confused if both sensors are active.
>
> >
> > 720K 5.25" v 360K 5.25": again, an issue of testing/certification,
> > similar to SS v DS. At least for a while, they were manufactured the same,
> > but were tested/certified for 48tpi or 96 tpi.
>
> I have had very little success in formatting 48tpi disks in 96tpi drives.
> As I mentioned earlier, this includes name-brands like 3M..

Interesting! I have never had a problem using even generic 48tpi disks
at 96tpi.
                                                 - don
 
> > Hard-sectored v soft-sectored: In a system that does not use the index
> > hole (Commodore, Apple ][), it doesn't matter. In all others, the only
> > way to use the wrong diskette would be to modify the drive to index off
> > of the spindle instead of using the sensor.
>
> Using hard sectored disks as soft-sectored should be possible. Just add a
> monostable and a couple of gates to only output a pulse when 2 holes are
> close together.
>
> In other words trigger a non-retriggerable monostable (with a time period
> of 3/4 of a sector time) off the trailing edge of the index pulse. AND
> the index pulse from the drive with the Q output of the monostable and
> feed the result to the controller.
>
> On the sector holes the monostable has already timed out, so the AND gate
> blocks the pulse. On the index hole, the monostable hasn't timed out from
> the previous sector pulse, so that one gets through.
>
> To do the reverse is a lot more difficult - you need to have the sector
> pulses accurately positioned wrt the data on the disk.
>
> I have thought about taking an old 5.25" drive (something that is not
> hard to get) and stripping it to get the chassis + spindle + disk clamp.
> Then mount a punch/die in place of the index sensor and a disk with
> suitable notches in place of the motor pulley. Add a detent on the drive
> to go into the notches. Line up the existing hole with the punch and die,
> set the detent into one of the notches, and clamp the disk. Now move
> round the notches and punch the extra holes. I must try this...
>
>
> >
> >
> > 3", 3.25": Many newbies will get sloppy in reference to 3.5" diskettes,
> > without realizing that there actually were 3" and 3.25" diskettes. 3"
> > were used by Amstradt, some non-US Canon?, and Amdek add-on drives for Coco
>
> The most common use in the UK was the Amstrad machines. But they were
> also used on the Tatung Einstein (I am looking at one) and on the Oric
> drives. And in some other machines, I'll bet (I have seen them used on a
> BBC micro).
>
> -tony
>
>
Received on Thu Jan 21 1999 - 17:15:46 GMT