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"2mb" Floppy Drive

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raoulduke

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I'm not really in the market, but I've seen these* a few times: www.ebay.com/itm/Mitsubishi-Apple-Macintosh-MF355F-592MA-2MB-3-5-Floppy-Drive-Internal-/231021618681. Is this just a labeling error? (per: http://lowendmac.com/2007/interchangeabilty-and-compatibility-of-apple-1-4-mb-floppy-superdrives/, which references the model number as a standard manual-inject floppy drive).

In other words it's just a standard 1.44mb drive and not some 2mb drive, right?

*There are multiple listings (I checked just now to make sure I hadn't seen the same one repeatedly). The second one I checked is a standard autoinject drive.
 
2 MB refers to the raw number of bits (in bytes) that can theoretically be placed on the disk.

However, much of this space is used by sector headers and "gaps" that let the floppy controller process data before the next sector comes up.

So the resulting amount left for the users is normally 1.44mb. Some formatting tools can reclaim some of this "wasted" space at the cost of compatiblity and speed.

Many vendors labeled their 3.5" HD floppy disks and drives as "2MB" because it sounded better than 1.44mb. The twisted marketing drones could claim the statement was "techincally" true.
 
To scratch an old itch, exactly what unit of measurement does 1.44MB refer to?

Consider that a "360K" drive has 720 sectors of 512 bytes. Similarly a "720K" drive has 1,440 sectors of 512 bytes. So, in this context, K = 1,024 (i.e. it's Ki). Now a "1.44MB" drive has 1,440 sectors of 1,024 bytes. So M = 1,024 x 1,000. What the hell kind of unit is this? If you go with M=1024*1024, then the drive should be called "1.41 (1.406 approximately) MB".--or just a "1440KB" drive. This was also a problem with early hard drive labeling.

At any rate, MFM recorded at a clock rate of 500KHz (2 usec per bit cell) on a disk spinning at 300 RPM gives you 100,000 bit cells per track, or 12,500 bytes per track. There are two tracks per cylinder and 80 cylinders specified as useful. Therefore 12,500 x 2 x 80 = 2,000,000 bytes. How one wants to break those bytes up into formatting information is left as an exercise; unlike the bastardized "1.44MB" label.

Some 3.5" drives are "3-mode" allowing for compatibility with the largely Japanese "NEC" convention of carrying the same format across from 8" to 5.25" to 3.5" media (a common-sense thing to do), so they can also spin at 360 RPM, resulting in a "1.6MB" drive capability. In all cases, M = 1,000,000.
 
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One of the standards for 3.5" HD floppy drives (ECMA-125) refers to the resultant device as 2MB. Apple officially referred to their High Density format as 1.4MB; Amiga had odd scheme to go for 1.76MB; and Acorn pursued a 1.6 MB format. Toshiba even went further by increasing the number of tracks to 84 but did not advertise their 3.5" HD drives on the basis of that higher capacity.

Floppies were incredibly fun as clever engineers and cunning marketeers often gave the opportunity to ensure disks couldn't be shared with other systems.
 
The slightly lower capacity of 1.4MB with Apple HFS floppies was due to overhead in the file system (forked files etc.). The low level MFM format is the same as PCs of the time. At least one company attempted a high density variable rotation speed GCR format of 1.6MB. Applied Engineering's AE HD+ drive supported it on a stock Apple IIgs using a GS/OS device driver.

BTW, those Mitsubishi manual inject drives are pretty unreliable at working with 800k GCR disks compared to the Sony drives.
 
Thanks guys, appreciate the info. I figured it was something like that - and I figured it'd have been a marketing ploy.

But I guess my real question was why people use that ploy now*? Who's going for high-capacity floppies now (as such - who isn't either using zip disks or maybe smartmedia adapters, or whatever - that's a narrow range of 'as such')? You have to figure the only people in the market are looking for specific replacement floppies for classic machines.

*I think I vaguely recall having known the 2mb raw data thing from at some point in my maybe youth. But now it's just confusing enough to potentially put people off from buying replacement drives. That's an at worst; at best it serves no purpose since anyone in that market would either already know this or look it up.

(*(cont'd) Honestly I just sometimes find seller strategies really interesting. I'm also really curious why sellers advertise 'working' machines without screenshots of the booted machine. I contacted a guy who was selling an SE/30 a few weeks ago. He said he just hadn't thought of it and would put one up - let's see if he did: he sure didn't... - and it still has not sold)
 
Maybe not relevant to this thread but there was the ED disks and drives which had an unformatted capacity of 4MB, 2.88MB formatted.
 
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mnbvcxz said:
Maybe not relevant to this thread but there was the ED disks and drives which had an unformatted capacity of 4MB, 2.8MB formatted.
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Yes, basically double the number of bits per track and the use of a different oxide/ferrite coating. Instead of a 500KHz clock rate, it used 1MHz.

But to answer raulduke's question, there are a number of reasons that floppies are employed. The first is universality--it's quite possible to write a floppy on a new machine (even if it uses a USB floppy drive) and read it on an old 5150. The encoding really hasn't changed. Another reason is that floppies are governed by an ANSI/ISO standard. A third is that they're cheap. A fourth is that they come from a time when a megabyte was a sizable amount of data (remember the discussion about the single-floppy bootable OS and browser that had both modem and NIC capabilities?).

Zip disks are far from universal, and, in fact, the IP is owned by Iomega. The same can be said of most flopticals as well as EZFlyer, Superdisks, UHD144 and other media. 650MB MO media died a log time ago. USB flash is making inroads, but not all legacy computers have USB and fewer can boot from them.

And floppies, if stored correctly, are remarkably robust. Whether or not a MLC flash drive will still be readable 40 years from now is something that's yet to be determined. Of course, by then, everything will be on/in the Cloud, with much of it lost forever.
 
No I didn't mean why would someone being using a 2mb floppy; I meant why would sellers label their auctions "2mb"? ChuckG, I meant nobody using floppies would be listing after capacity (at this point, even with a floppy drive - I think the smartmedia adapter is universal - to HD 3.5").

Mnbvcxz that's true although I feel like they had a more common name. There might have been a higher capacity one also.
 
Because that's industry-standard terminology. It indicates the raw data capacity of the floppy at a standard data rate and encoding, no matter how it's sectored. For example, I can take the same floppy and sector it with 256 or 1,024 byte sectors--most controllers are perfectly capable of doing that. The formatted capacity changes, but the unformatted capacity remains the same.

Have a look at the OEM manual for a common "1.44MB" drive. 1/2/1.6MB stated.

USB floppies have the format hard-coded, so they are an exception, but a standard "legacy" floppy drive is a very dumb device and pretty much doesn't care what comes over the READ DATA and WRITE DATA lines.
 
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raoulduke said:
No I didn't mean why would someone being using a 2mb floppy; I meant why would sellers label their auctions "2mb"?
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1) 2MB is the correct term according to the standard.
2) More is always better.
3) To remind people who have other (non-PC) systems that this floppy might work with their system as opposed to some USB 1.44MB floppy drives which only work with that single format.

Though if you think people advertising floppy drives now on the basis of the theoretical capacity, there are a number of websites where people try to prove the actual maximum data storage limits even at the expense of reliability, interchangeability, or even destruction of the drive.
 
Mind you, that's only the convention, dictated by usual practice. For example, I think it's a lead-pipe cinch to get the raw track capacity up by 50% by resorting to different encodings (RLL or GCR), kicking the clock rate up a bit (modern drives have less "jitter" in both the R/W electronics as well as ISV in the drive motor). But you would sacrifice the universality of the medium.
 
Up to 1.68MB formatting actually works fine in any standard 1.44 MB floppy drive. Even in Windows Xp. :)

Some more is possible, but many operating systems cough up on it.


here's trial version of a tool. Only 30 days of trial, but should be enough to format a few thousand floppies...

http://www.alkonost.com/maxformat/


Under DOS there were also 2M and 2MGUI which would lead to a floppy with "nearly" 2MB capacity in a 1.44" floppy drive. However, these were generally not compatible with Windows or many other systems.
 
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2M and some of the other super formats wrote the entire track at one time or had to write the entire disk at one time. Acceptable for install or backup diskettes but awkward for normal operation of a floppy only system, especially with smaller amounts of memory.
 
I corresponded with Ciraco back in the 1990s and have one of his first beta versions in my files. The way this is done (as well as IBM XDF) is that, if you read the NEC 765 datasheet, you'd think that a disk must have sectors of the same size on a track. Fortunately, that's not true--the "format track" command will write n sectors to a track according to command parameters, but use a table of 4-byte entries to actually, without inspection, write the ID headers. So if a header says, for example, that the data field is 1,024 bytes, when it was formatted as list of 256-byte sectors, subsequent write commands will blindly write 1,024 bytes for that sector, over-writing a couple of other 256-byte headers. So, by keeping the gaps small, you can fill a track pretty full.

I wouldn't recommend a format like this for routine read-write use, but as a read-only medium, it's no less reliable than any other conventional disk format. Thats why both IBM and Microsoft used similar schemes (XDF and DMF). Once you've written the data and verified it, you're okay. Just don't try to over-write anything.
 
I have a 2.4MB 5.25" IBM Floppy drive in my DOS PC. I bought it because it was cheaper than a nice black 1.2MB on eBay, and it works just fine as a 1.2MB drive. I don't think I can use it as 2.4MB via DOS, though.
 
Yeah, as I understand the those things, there's an addition position on the interface to drop the 360 RPM 1.2 MB spindle speed to 180 RPM. So, with a little driver scribbling, you could conceivably write a 2.4MB floppy using HD media on the thing. But why?
 
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