[Coco] [Color Computer] Re: using 1.44 floppy drives

[Dave]

>From macfaq.org ->

While it's physically possible to do it, those of us with a great 
deal of experience with Macs almost universally recommend against 
it. If you absolutely need an 800K disk and only have 1.4MB floppies 
available, you can force a 1.4MB disk to be an 800K disk by taping 
over both sides of the hole opposite the write-protect tab. THIS IS 
ONLY A TEMPORARY SOLUTION. THE DATA ON DISKS FORMATTED LIKE THIS 
WILL NOT USUALLY SURVIVE FOR LONG. UNDER NO CIRCUMSTANCES SHOULD YOU 
USE FLOPPIES FORMATTED LIKE THIS FOR STORING DATA LONGER THAN A FEW 
WEEKS. Don't say I didn't warn you... 

Tom Lee of Stanford has graciously provided the following 
explanation: 

To clear up the persistent confusion and superstition about 800K vs. 
1.44MB media, here's the correct story: There is about a ten percent 
difference in the magnetization thresholds (called "coercivity") for 
the two media, with the 800K stuff having the lower value. If you 
want to get technical, 800K media have a nominal coercivity of 650 
oersteds, versus 720 - 730 oersteds for 1.4MB media. So, 800K drives 
may find it difficult to write on 1.44MB media. However, ten percent 
is not a large difference, and in fact, is about the same as normal 
variations within a batch from a given manufacturing run. Plus, 
coercivity varies with temperature, too. So, the two media are not 
as wholly incompatible as lore has it. 

However, if a 1.4MB disk has ever been written on by a 1.4MB drive 
(and this includes formatting), an 800K drive's weaker write fields 
may not be strong enough to reliably over-write the existing data, 
and you'll have flaky behavior (particularly if you're unlucky 
enough to have a drive with write currents at the low end of the 
spec, trying to write on a floppy with coercivity at the high end of 
spec). But if the floppy is virgin, you'll rarely see any problems 
at all. You can "re-virginize" floppies if you have a good 
demagnetizer handy. 

Now, if you go the other way, by melting or punching (don't drill!) 
an extra hole to trick drives into thinking an 800K floppy is really 
1.4MB, there's no problem with the drive's ability to flip 
magnetizations properly. However, the higher density is achieved by 
packing adjacent bits more tightly together on a given track (but 
the number of tracks per side is the same -- 80 -- for 
400K/720K/800K/1.4MB media), and the lower density media may not 
have fine enough particles to do the job well (and the lower 
magnetic field strength of those particles further degrades margin). 
That's why many advise against doing this operation. 

Since both media types are readily available (the 800K stuff is the 
same as 720K media from the PC world, but you'll have to reformat as 
Mac if they come preformatted, as they usually do nowadays), there's 
no real reason to do any of these things. But, every once in a 
while, you'll find these hacks useful in an emergency. 



--- In ColorComputer at yahoogroups.com, "stacey" <allencoco at y...> 
wrote:
> my question is can you use a 1.44 floppy on the coco if you use 
720 
> media   or can you use a 1.44 flopy with 1.44 media with the high 
> density hole covered upu
> 
> i would use a 720k drive but all i have are 3 tandy  drives 3.5 
out of 
> a old tandy 1000 hx but need  some 5.25 brakets to use them
> 
> does any one know hwere one could get 720k media and drives still 
and 
> the 5.25 brackets
> 
> also im looking for coco software and a fd-501 disk system
> 
> thanks
> 
> email to allencoco at y...




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