Do you double side your floppies?

[Schema]

Good point Boray!

I have one of those little disk-notchers that puts the hole in exactly the right place, and double-side most of my 5 1/4" disks. Been doing so for 15 years and haven't had a problem.

[ral-clan]

The magnetic field doesn't 'wreck' the data of the bottom side, because like in the following schematic:

Code: Select all

  Head
V      A
V      A <- magnetic field
V      A
--------
 >>>>>>  <- top magnetic surface
--------

         <- plastic carrier

--------
         <- bottom magnetic surface
--------

the top magnetic surface acts like a short circuit to the magnetic field.

I didn't know a substance could actually block a magnetic force from "radiating" any further....

Is it like one opposing magentic force meeting another....i.e. they cancel each other out? Like when you put the opposite poles of two magnets together and they repell each other?

Of course, this is on the understanding that the disk surface itself is slightly magnetic....which I might be wrong in saying.

[carlsson]

Consider that drives like 1571 (at least in C128 mode) and of course 5.25" drives for other, non-Commodore systems, often are double sided with dual R/W heads. If there was a risk of data leak, those systems would be at great danger from day 1.

[Jeff-20]

Hmmm.... Do you store just 720kb on a 1.44MB diskette as well?

I guess I should start using the other side of my datacassette tapes too. . . ?

[carlsson]

Perhaps there is an increased risk of the tape breaking, the more you use it and playing both sides. If you are superstitious, you should only use one side of the tape etc.

[Boray]

Tapes - Do you mean you actually don't use both A and B sides of the tapes? Or do you mean that you don't open it up and turn the tape over so you get four sides?

/Anders

[carlsson]

Is there even magnetic coating on the inside of an audio cassette tape? It is a big hassle to fix an entangled tape, much less spool it the other way.

[Jeff-20]

Tapes - Do you mean you actually don't use both A and B sides of the tapes? Or do you mean that you don't open it up and turn the tape over so you get four sides?

/Anders

I am just kidding. Of course I use side A and side B. Tapes have a redundant feature that makes them seem a little more reliable for long term storage and use. Still, I spent most of my childhood fixing entangled music tapes (after my tape deck would eat them). I've only had 2 disks fail on me. I still have them in hopes that someday I can rescue the data.

[Mike]

The magnetic field doesn't 'wreck' the data of the bottom side, because [schematic deleted] the top magnetic surface acts like a short circuit to the magnetic field.

I didn't know a substance could actually block a magnetic force from "radiating" any further....

Is it like one opposing magentic force meeting another....i.e. they cancel each other out? Like when you put the opposite poles of two magnets together and they repell each other?

Of course, this is on the understanding that the disk surface itself is slightly magnetic....which I might be wrong in saying.

This comes from the so-called 'magnetic permeability'. It's a number, that can be measured for each substance, how much a magnetic field is enforced by the substance. I won't delve too far into physics here, but for magnetic fields it is more or less like the inverse of electric resistance for electric currents. (<- engineers view )

Vacuum is assigned the value 1, while most ferro-magnetic substances do have a value of 1000 or more. Alike to a electric short-circuit, the magnetic field thinks: "Oh, this is much a nicer way, let's go here."

And thus it doesn't touch the bottom magnetic surface.

You can try the following experiment:

2 Sheets of Cardboard.
1 Sheet of Iron (could be the top lid of a tin can)
1 Strong magnet.
1 Paperclip
several books.

build the following arrangement:

Code: Select all

Book                              Book
--------------------------------------  <- top layer cardboard
----                              ----  <- distance pieces from cardboard
--------------------------------------  <- bottom layer cardboard
Book                              Book
Book                              Book
Book                              Book
Book                              Book

Check, that the magnet attracts both the iron sheet and paper clip. Then place the magnet atop the cardboard, and hang the paperclip from below into the field. The magnetic field passes the two sheets of cardboard and will hold the paperclip.

Insert the iron sheet between the two cardboards, and see what happens ...

Michael

[ral-clan]

The magnetic field doesn't 'wreck' the data of the bottom side, because [schematic deleted] the top magnetic surface acts like a short circuit to the magnetic field.

I didn't know a substance could actually block a magnetic force from "radiating" any further....

This comes from the so-called 'magnetic permeability'. It's a number, that can be measured for each substance, how much a magnetic field is enforced by the substance. I won't delve too far into physics here, but for magnetic fields it is more or less like the inverse of electric resistance for electric currents. (<- engineers view )

Thanks for that great explanation! I had NO IDEA that a magnetic field could be "coaxed" or "persuaded" in that way!!! I thought it was basically an immutable radiating force. The things you learn!

[Jeff-20]

I love home experiments!

[saundby]

Some notes on floppy terminology:

The "floppy" is, to engineers, the drive itself. The media is the "disk." So when referring to a double-sided floppy in general the reference is made with respect to the capabilities of the drive, not the media.

The media manufacturers, however, were quick to exploit the misunderstanding on the part of the typical buyer and price-grade their media according to the customer's drive. It was often said that if a piece of media was bad on one side it would be sold as a piece of single sided media. In fact, my experience was that any piece of media which fell out was disposed of, and that good media was labelled and packaged according to market demand, not the media quality. There may have been minor differences in the jacket used for single-sided and double-sided disks.

The primary issue that gets raised concerning the use of both sides of a disk (regardless of whether it is labelled for use in a single or double sided drive) is that when you flip the disk and put it into the single sided drive you're reversing the direction of spin and potentially knocking crud out of the wiper in the jacket and releasing it into the wild where it may do damage to the disk surface. While this is true, the risk here is only an incremental increase over the risks normally faced by floppies that are placed in drives in rooms with cigarette smoke, burning steaks in the oven, and Dorito-dust covered fingers handling them.

Basically, if you use good practices in protecting your disks in general, then using them both ways in a single-sided drive will not be a problem.

As to densities, there is no difference in the media for single or double density. They both record data at the same frequency. In single density recording FM encoding is used. In FM, there is a regular clock beat placing transitions on the disk. In between each clock beat there is a data bit--a transition for a one and no transition for a zero.

In double density both the clock and data bits carry data. There are several different MFM (Modified FM) approaches used, but the idea is to start using that clock bit as part of the data encoding. The frequency of the data transfer is the same as FM encoding, however. So the media is unaffected regardless of whether double density or single density encoding is used. It all happens in the computer's electronics, the disk doesn't see data at a different rate.

High density or quad density disks are a different matter. They are built to have twice as many or more tracks per inch than prior 48 TPI media, and the coatings are different to allow the media to record a signal with a smaller magnetic flux.

So, in essence, there is no media difference between any of SSSD, DSSD, SSDD, DSDD disks, only labelling differences.

GCR is also something that happens in the electronics, not at the media surface (and the same with RLL, both of which are loose terms that can refer to several different things with respect to data recording.) In Commodore's GCR they are increasing the data density of their disks by encoding 5 bits of data for every 4 bits of data they write to the disk (as opposed to the original IBM 9-track tape GCR that used five bits of data to record four with error correction.) This is what gave C= a 170K disk when Apple had a 130K disk (and that was after Woz had applied some tricks to get that much data on the disk.) The GCR codes are essential self-clocking data, which is what lets this trick work.

Now, if C= could only have sold us 8050 drives for Vics and 64s for under $1000, we'd never have missed the lack of hard disks, and we'd have even more formats to worry about...

-Mark G.

[carlsson]

So, there has never been any single density disks sold? It explains a bit.

Does the 15xx series drives use FM or MFM? The only reference to single density (thus plain FM) I saw was in an issue of Your Computer comparing disk drive solutions for various systems, but they may have got things wrong. The 5:4 ratio on 34 tracks giving 166K+ capacity (not counting the directory track, which can hold data with some programming tricks) suggests it is MFM after all...

[Bacon]

Some notes on floppy terminology:

The "floppy" is, to engineers, the drive itself. The media is the "disk."

While that may be how things have evolved over time, the original use of the word floppy referred to the disks themselves -- the disk in a Winchester (or "hard") drive were, uh... hard, and the new removable disks introduced in the early 70s were soft and flexible, i.e. "floppy".

Since we discuss an ancient computer and its accessories here, I think it's perfectly appropriate to refer to the disks as "floppies" and the drives as, well, drives. Makes much more sense too. After all, it's the disk that's bendable, not the drive.

Isn't it fun nitpicking over semantics?

Edit: Besides, I've been calling the disks floppies for >20 years, so I'm not likely to change now.

[Schlowski]

Just to give my comment:

I always thought that 'disk' is the round thing which rotates (and is related to discus, so I'm always wondering if it's disc or disk), this comes in 'hard' and 'soft/floppy' flavours and there are drives to use them - hard disk drives and floppy disk drives.

And yes, I like

nitpicking over semantics

too

Björg