37

This was a good piece of production engineering. IBM expected to sell lots of twin-floppy PCs, even after the launch of the XT (personal experience in a UK reseller in late 1984). To assemble a twin-floppy PC and have the drives respond correctly to the drive select wires in the cable, there are four choices: Pay the drive supplier to jumper "left"...


34

Anecdotal evidence (*1) We had a bank as customer with branch offices all over the state. These were the 70s, the final years of batch only, although, already using remote batch with local data acquisition and storage. In this case all daily bookings were collected on 8 inch floppies (well, one was enough for a days work). Some when during the late evening ...


30

I did some assembly development on a dual-floppy (5 1/4" double-sided) IBM PC 5150 in 1982/83 (PC DOS 1.1 and onward). Boy, did that exercise the floppy drives! We wore out floppies all the time and soon settled on using only Verbatim brand as those seemed to last the longest. Even with Verbatim, heavily used diskettes lasted maybe a month before they ...


25

My 1980 edition of the Apple II DOS manual mentions that, for a 5.25" disk: With reasonable care a diskette will give you an average life of 40 hours——which is a lot, when you consider the few seconds it takes to LOAD most programs. There is no source for where they got that figure from.


21

On the C64, no. On power up, the drive is resetting and the motor may spin briefly, but the drive is not actually reading the disk. And even if it were, it is an IEC slave device and cannot initiate communication with the C64/C128 bus master itself. For an auto boot concept to be implemented, it would have to be the computer's kernal directing the flow of ...


17

There seems to be some confusion about how this worked clouding the categorization of what to call it. Let's compare the interfaces between how Shugart designated signals at the drive (and how other makers used them) vs how IBM re-designated them at the controller in order to support the twist idea. (I've used A and B on the IBM version to reduce confusion) ...


16

It sounds like some blocks on the disk (particularly the ones containing directory information) are okay, but some (containing some file data) are not. This is a data recovery situation. If you boot from a Linux LiveCD (or a flash drive built from one), you should be able to use the ddrescue tool which is designed for exactly this situation. It will find ...


13

A sector is the minimum amount of data you can read from a floppy disk or harddisk. As you've drawn correctly, a sector is part of a track (on a harddisk also called cylinder, because there are many platters with one track, so overall you get a cylinder). One thing you are missing is that some floppy drives and nearly all harddrives have multiple heads, so ...


12

You can get a relative ordering by looking at DOS versions for the drives. IEEE-488 drives 2040 - first drive, 5.25"x2@170K, 1979, DOS 1.0 3040 - 5.25"x2@170k in Europe, 1979, DOS 1.2 4040 - 5.25"x2@170k, 1980, DOS 2.0 2031 - 5.25"x1@170k, 1980, DOS 2.0 4031 - 5.25"x2@170k, 1980, DOS 2.0 8050 - 5.25"x2@521k, 1980, DOS 2.5 8250 - 5.25"x2@1042k (double-sided)...


12

These are disk- and tape images files for the Commodore 64 and computers using the same floppy drives and disk formats, like the VIC-20, or the Commodore 128. D64 are single-sided 5.25" disk images ("1541 images" for the Commodore 64), sometimes also called D41. D71 are double-sided 5.25" disk images ("1571 images") D81 are double-sided 3.5" disk images ...


12

These are headerless sector dumps of the 360KiB disks, and can be written directly to the appropriate floppies. Since you’re using Windows 98, I suspect the best tool to do is ImageDisk. You’ll need to convert the images first: BIN2IMD ATDOS331.360 ATDOS331.IMD DM=5 N=40 SS=512 SM=1-9 /2 (250kbps MFM, 40 cylinders, 512 bytes per sector, sectors mapped ...


12

Many USB floppy drives will not read double-density (720 / 800 KB) disks at all. Most that can will only read 720 KB disks formatted for IBM PCs. I am not aware of any standard USB 3.5" drives that can read the 800 KB double-density Mac format. They are unlikely to exist as 800 KB disks as used on the classic Macs use a proprietary on-disk format ...


11

KB entry Q75131 provides the following answer for MS-DOS FORMAT: 320: 320-KiB (40 tps, 8 spt) DSDD 5.25” floppy 360: 360-KiB (40 tps, 9 spt) DSDD 5.25” floppy I don’t know about the Windows-only 640 format.


11

OK, this is very dusty material in my memory, so I'm relying a bit on Google/Wikipedia here. I may be able to find some of my printed documentation, but it will take a while. The granule was the allocation unit for the filesystem. I don't remember the granule size on single-density drives, but Wikipedia says for double-density drives it was 6 sectors per ...


10

Thanks to RichF's answer I looked for information specifically on booting OS-9 and found that you definitely did have to manually launch even an alternative operating system. From OS-9 Level Two Operating System page 2-2, "Booting OS-9": However, this DOS is not a filename and this is not how you load or run any other program. These are the normal ways: ...


10

I support DMK in my MSX emulator, and bear in mind that it's a bit of a confused file format. It has a bunch of design deficiencies, and was clearly tightly coupled to the program that originally implemented it. But starting with the perfectly sensible stuff: The first 16 bytes are the header, which you seem to be familiar with — write protection, geometry, ...


10

Having the desired pins aligned on the pin out nicely enough to make this happen suggests, that this was intentional at least to some degree. Since the pinout is an IBM one, made especially for the IBM PC (*1), and this twisted cable was used from the very first PC model, it's pretty clear that it was done on purpose. Interlude: hack or intended design? ...


9

The 2.88MB "extended density" disks have a different type of coating on them, which normal "high density" drives are not optimised to read or write. So you might not reliably be able to format it even for 1.44MB. I believe these disks were never common and are now decidedly rare, as are the drives to work with them. A 1.44MB drive is also not designed to ...


8

I’ll limit my answer to common 3.5” formats on PCs, DSDD, DSHD, and SuperDisk, as listed in your question. SuperDisk drives can be ignored as far as backwards-compatibility is concerned: they have two head assemblies, one for “standard” formats, the other for LS formats, and the “standard” head is equivalent to a high-density 3.5” drive’s. The main concern ...


8

Some USB floppy drives don't support double-density floppy disks (as opposed to the newer high-density disks that are usually formatted to 1440KB). I think it's usually a limitation of the controller chip interfacing between USB and the drive itself. You should try using a different drive, and look specifically for reviews of its performance on double-...


8

A partly speculative answer, working backwards from the source code of Marat Fayzulin's ColEm, it appears to be a fixed-size sector dump. On line 52 of EMULib/FDIDisk.c you can see confirmation of the geometry you already know about: single sided; 40 tracks; 8 sectors per track; 512-byte sectors. Line 406 lists FMT_ADMDSK (i.e. Adam disk) amongst those ...


8

Definitely a hack. A systems with floppy disk drives had separate selection wires in the connection cable, where one of them was to choose between on of 2 or 4 drives connected in parallel. There was a jumper on the drive to activate one of these wires resulting in an address. Setting up this jumper was somewhat error prone and also extra work. The trend was ...


8

Sectoring on disks predates floppies. It was in widespread use on hard disks by the time floppies came around. Also, I would note that everything from 1 byte/word granularity to track-sized sectors has been argued for (and sometimes used) over the years on both floppies and hard disks. Still, why did it settle largely on 512? First, it's just as neat as ...


7

Provided that's the only thing that happened to them, can I write disk images to them in attempt to restore it Yes. However, it's rare for floppies to just "loose magnetic charge", unless they have been stored somewhere where they were exposed to magnetic fields, or other unfavourable conditions that caused this to happen. Though the magnetization does get ...


7

I don't know the MicroBee, but grew up with CP/M 2.2 and 3.0 and its variety of floppy disk formats. There were two different ways of implementing skew in use: assigning the low-level sector IDs in a non-contiguous order, and simply access sectors by a 1:1 mapping from their logical number, resulting in sector ID sequences like 0 3 6 9 2 5 8 1 4 7, ...


7

Note: The solution below ultimately failed to work for the asker as-is. I presume this is because my printable auxcopy binary was not written well enough to operate correctly on bare hardware (it was only tested in a VM); perhaps this flaw can be easily corrected, but I am not yet able to see how. Nevertheless, as it seems to have served as a major ...


7

Can't really put a figure on it. I've had the same disk in a portable USB 3.5" drive for 5 years which I used for installing licence keys on numerous machines and uploading to a database. Doesn't this depend on whether the disk is spinning continuously or whether it just starts up, reads/writes the data and then stops. I seem to remember the 8" ...


7

As I understand it, the head rubs against the disk and the disk rubs against the shell/sleeve when in operation. Correct. But the head is only rubbing against the disk when data are being transferred (either reading or writing). On an 8" or early 5¼" drive the read/write head (or heads on a dual-sided drive) is only pushed against the disk by a ...


6

In fact, you can use any of these formats (up to 1.44MB) on a 3.5" or 5.25" DSHD floppy disk. For the 40-track formats, an 80-track drive would need to double-step; for the single-sided formats, only one head of a double-sided drive would be activated. There are even extended formats which fit, say, 1.6MB in by using a still-higher number of sectors per ...


6

While it is "flat out wrong", they do preface this with: As this manual is primarily concerned with software, no attempt will be made to deal with the specifics of the hardware. For example, while in fact data is stored as a continuous stream of analog signals, we will deal with discrete digital data, i.e. a or a 1 . We recognize that the hardware ...


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