How to read and write old floppy disks

Introduction and considerations

This Web page last updated dated Jan 10 2019, this introduction added June 7 2024. This page is about ways to read and write "old" floppy diskettes (disks from systems of the 1970's and 80's); using means of hardware and software which was available on computers and devices either vintage (20th century), or into the early 2010 years.

On another Web page, I have a lot of information about original floppy drives, diskette media, and various issues including vintage floppy controllers. Also on that Web page, there is a section Windows/Linux floppy disk controllers & software, versus USB microcontrollers, which mentions but does not describemodern USB-based floppy controllers, hobby projects, and floppy drive replacements. Those are outside my interests, skills, and ability to keep up with. I compare and contrast the two, and that may be informative to vintage computerists, or people with old disks to recover files from. Of course those are my opinions and contain my biases.

You may need a Web search, to find all my Web pages of interest on this subject. If you add to your Web search string, "", your search will be limited to pages on my Web site.

To contact me, or for ordering information follow this link.

"I want to read old diskettes on my PC/Windows/OSX/Linux machine"

Some people ask: "I want to read 5.25-inch or 8-inch diskettes on my PC/Windows/Linux machine. Please sell me a complete system, or tell me where to get one." Some people ask: "I have an 8-inch drive, sell me the power adapter and cable for use with my modern computer." Often they have no idea how this might be accomplished beyond those statements. Some people want to read CP/M or other non-MS-DOS 5.25" or 3.5" diskettes, or old Mac 400K or 800K 3.5" Mac diskettes, on a Windows PC. A few people want to read really ODD formats - hard sectored, M2FM, and so on.

Folks, this is not a "plug and play" project. You can't just "plug in" something and it magically "works". Sorry.

Up to the early 21st century, say the 2010's, you had four choices to accomplish the above goals.

Choice one: contact a "data recovery service" (or find some vintage-computer techie) and tell them everything you can find out, about the origins of those diskettes, including the programs and operating system(s) used to produce them. They will presumably offer to "convert the disks" on some kind of terms, and then process your diskettes for you. They will presumably hand you the files for some fee, and for an additional fee may be able to "convert" the files for use with modern "applications" (software). Be sure you know what to expect, as in any transaction. Proceed entirely at your own risk of loss of diskettes, data, and or money.

Choice two: Buy some special-purpose, private-produced, or hobby produced, floppy drive interface for 3.5" or 5.25" floppy drives for use on a modern computer. This may be a custom or hobby "microcontroller that supports or emulates floppy drives". (See all the notes below.) Add a cabling adapter to make 8-inch floppy drive connections if you are working with 8-inch floppy drives. Most of these devices, don't directly support 8-inch drives. Use the software offered with the interface to collect "data". The software may or may not be able to "interpret" the data on the diskettes into files; you'll need additional software possibly, from another source. You will likely need to be a computer programmer with hardware experience, to make this choice "work", and you may not be successful. And when you are done, you still have to convert the files extracted, to something a modern program can "understand".

A variation of this "choice", is to use some general-purpose microcontroller (Arduino, Rasberry Pi, PIC, etc. etc.), or a "hobby" logic-analyzer module, connected directly to a floppy drive. Then use software or scripts to run the device to operate the floppy drive, "sample" the tracks and build a sampling file. Then use additional software to interpret the sampled file back into sector-data and build an "image" of the original diskette. I discuss this option in a generic way, later in this document.

Choice three: get an older PC with an internal floppy controller, or add to it an ISA-card floppy controller. (There's not many PCI floppy drive controllers. Add that 8-inch adapter if necessary, as noted above. Find and use some ancient PC software in MS-DOS to "handle" the odd format under program control. Or use Linux and its binary file tools, which won't produce "files". ...and you still have to convert the file data if your goal is to use the data today.

Choice four: on that older PC with ISA slots, find some ancient hardware floppy controllers, and software that reads non-MS-DOS disk formats. Many of those hardware controllers, were developed to "unlock" or "crack" copy-protected diskettes. Example: Copy II PC Deluxe Option Board. It's a special floppy controller which sits on an ISA slot card. Using the software, you can write and read Mac 800K disks. The manual for the product is "out there" on the internet. (Thanks to Gregory Robertson for this information.) Some ISA floppy controllers are more capable than others.

Neither solution two or three, lets you use the odd disks like "normal" MS-DOS diskettes, for example through Windows Explorer. (Some Linux solutions let you "mount" some diskette formats, some not.) The rest of this Web page, describes some of the options and hardware and software suggested above. A few odd things are described immediately below.

Note on 8-inch "adapters" or "cables for PCs" To read 8-inch floppy drives on a "PC", you MAY be able to connect 8-inch drives to a PC's internal floppy controller (if it has one). But you need an 8-inch drive, with power supply, in a cabinet; a 50-pin cable for the 8-inch drive; a wiring adapter for the 50-pin cable to your 34-pin floppy controller; and software and software knowledge! Even with that, MOST PC floppy controllers won't read old single-density format anyway! See this section for additional details; the rest of this page for more details.

Note on reading "disk formats": Reading non-MS-DOS disks on a PC, even with the right sized floppy drive "properly" connected, can be difficult. The floppy CONTROLLER on the PC, which does all the work of reading, writing, and formatting, may not be able to accept non-MS-DOS formats, even WITH software. Some early disk formats including Apple's, use non-"standard" diskette formatting. Your floppy controller may not accept single-density. Some diskette double-density formats, include boot-track(s) in single density. Or it can simply be a problem with knowing which of the MANY MANY CP/M or other disk formats you need to use with your particular diskettes.

Note on USB floppy drives: Most of these are only intended for use with 3.5" floppy diskettes and to read/write MS-DOS 1.44MB formats. Only the very earliest, used an unmodified 3.5" floppy driveand *might* be adaptable to 5.25-inch drives. Otherwise they cannot be "reprogrammed", they cannot be adapted to a 5.25-inch drive.

If what I've just described is unfamilar technical language, look at my Web page on floppy disk technology for some background information.

I've now provided some general descriptions and "keywords", about "cabling" old floppy drives to a later 20th century computer, "to read old floppy disks". You can use this and other information to find more information and increase your understanding. Then you can decide to do this work yourself; or you will be more informed when asking others to do this work. It's your data, your time and money - your decisions. Further notes on specifics I've mentioned are below and on other pages on my Web site.

discussions about converting from 8" and 5.25" drives to 3.5" drives

In Feb 2005 there were some discussions in popular newsgroups, about converting old CP/M systems from 8-inch and 5.25-inch floppy drives, to 3.5" drives and media. Issues raised included support of FM or single density; finding old media; choices of formats. I decided these discusssions were worth preserving, as these issues come up over and over. One discussion was in the Classic-comp CCTECH discussion. The other occurred in Usenet discussion group comp.os.cpm.

a good Web site for using 8-inch CP/M diskettes on PC's is my colleague David Dunfield's Web site. Check my discussion of Dunfield's disk site elsewhere on this page.

It can be a challenge to use 5.25-inch "quad density" drives on modern computers, or modern floppy drives on older computers. The Web page linked here describes how to adapt a Teac FD-55GFR 1.2M drive to use for 800K (96TPI) formatted diskettes. Other notes there may apply to other brands of 1.2M drives. Note that the Web page is copywrited by the author, the Web link is to a licensed copy of that work.

Further details

5.25-inch to 8-inch cabling adapters

8-inch drives use most of the same signals as 5.25 inch drives. So old PC floppy controllers, can be adapted to operate even older 8-inch floppy drives, by "adapting" signals from the 34-pin connector of the 5.25 inch drive, to the 50-pin connector of the 8-inch drive.

Some people build these 34-pin to 50-pin adapters, you could build one. The CP/M FAQ has a diagram; I've not checked it so no guarantees. Here's a copy of the description from the CP/M FAQ. Dave Dunfield's specific notes for attaching 8-inch drives to PC's are at at this Web page under "Notes on connecting 8 inch and external floppy drives".. You may find problems adapting this to specific drives, as some signals may be used differently. This is not a "plug and play" solution! No guarantees! That's why my Web site has all this information and references, OK?

If you want to buy such an adapter, look around the Web for persons or small companies who offer such a thing. Again - it is just wires, not a "controller" or a "magic cable that connects your PC to an old floppy drive". Contact me personally, if you want suggested sources for such adapters.

Notes about 8" drives on "modern" PC's: 8-inch floppy drives required a 150-ohm terminator. That's a set of resistors in an IC package, read about them on another Web page.. They act as pull-ups for the open-collector driver ICs on very-old floppy controllers. Now, "modern" PC-compatibles, expect to "drive" 3.5" and 5.25" floppy drives. Those use 1000-ohm or so terminators. operate 8-inch drives on modern PC's, you will likely need to change the terminator to a higher value. Thanks to Michael Zahorik, who most-recently pointed this out, as his Shugart 800 drives on a PC controller, were not reading well on the innermost tracks, until he changed the terminator to 1K ohms.

floppy drive controllers with conversion, imaging software

Some years ago, there were a series of floppy controllers for PC/Windows systems branded as the Compaticard product line. Some of them used internal floppy drives, some supported external floppy drives. Some of them could read Apple II and Mac diskettes. In any event, these products are long out of production and rare and are "ISA cards" only usable on VERY ancient PC-compatibles. So I don't "cover" the Compaticard here on this Web page. Same things apply to Central Point Option Board products. Search the Web.

SOme CP/M systems (and systems like the Apple II) used disk formats that conventional floppy disk controller boards can't read. There is/was a program and a bit of hardware called "Disk2FDI" which is described at this Web page. It uses a PC and a cable between a 5.25-inch floppy drive and the parallel port, and is said to be able to read Apple II and Commodore diskettes. A trial version is free to read only; there is a registration fee to get the registered version, from Europe.

Since about 2008, there's been a number of hobby-class projects to use programmable logic devices or embedded microprocessors as programmable floppy controllers. See my notes below.

Software to read/write foreign diskettes on 1990's PC's under MS-DOS

IBM-PC compatibles of the 1990's and into the 2000's, provided a 5.25" or 3.5" floppy drive as 'standard'. The drive was operated by a "floppy disk controller" which was either a card (ISA, PCI) on the computer's "bus slots", or it was part of the motherboard's hardware. A number of software tools were developed in the period, to read and sometimes write non-MS-DOS diskette formats. Those tools ran under OS's like MS-DOS or Linux or Windows. I've collected information on some of these now-ancient products here. Look in the above section for add-on hardware for PC's to read foreign floppy diskettes. Caution: the floppy controller you attempt to use with this software, may not accept single-density. Some diskette double-density formats, include boot-track(s) in single density. Some of the software below, may be confused by mixed-density format.

Sydex's ANADISK and 22DISK; Teledisk

One software product to read old CP/M diskettes was developed and provided by Sydex Inc. and called "Anadisk" and "22disk". This product was produced in the 1980's to run under MS-DOS. It was offered in "freeware" trial form at no charge, as well as a licensed form for a fee. By the 21st century, the rights to the products were sold and it's no longer available. "Freeware" versions have been removed from many archive sites. But the originator of these products offers some degree of support to ORIGINAL licensees. Check this Web page for further history and discussion, including my correspondence with Chuck Guzis, president of Sydex and author of these programs.

"Teledisk" was another classic commercial product, to read and write "foreign" disk formats in the MS-DOS world. I don't have in hand the history of that product. But copies of Teledisk, and images collected in ".TDO" format, appear in many vintage computing archives.

Dave Dunfield's imagedisk

Check my "how to CP/M" Web page for more discussion of Dave Dunfield's MS-DOS-based imagedsk or imagedisk tools and his archive of system disk images. Dave's program, on a vintage MS-DOS computer with then-ordinary floppy controller and drives, transfers disk contents to and from an "image" file. Thus his program can recreate the original diskette. He also has software tools on his site to test PC's floppy controllers and drives to support single-density operation, which is not not supported on some vintage PC floppy controllers. This has become the primary tool for CP/M and other 8-bit system disk imaging and archiving. Dave's site has many "boot disk" images, plus means to support 8-bit systems with MS-DOS PC-incompatible floppy controllers.

Linux "raw" diskette utilities

My ignorance of Linux is vast but I'm not clueless. Linux has some raw "file system" tools at the command line level (they call it "the shell" or "the console") called simply "dd". There's also some vintage tools from Unix days for CP/M diskettes, called "cpmtools". Tools like "dosbox" will emulate MS-DOS to run MS-DOS-based software. There's similar emulators for CP/M-based software. Linux will also run some "Catweasel" hardware and software, discussed elsewhere on this page.

A more knowledgable colleage of mine, discusses dd, cpmtools, and working with Dunfield's IMG Imagedisk images, on a web page on his Web site. Mike Loewen shows how to read off old IMSAI CP/M disks with a mix of Imagedisk and Unix/Linux tools. Note that hardware-operating tools like Imagedisk, Catweasel, etc. must run "native" and not under emulation.

Omniflop and Omnidisk, software to read non-PC diskettes

Omniflop is a freeware product to read foreign diskettes on Windows-based PC's. Check the Web link for details. They have an older product, Omnidisk which runs under MS-DOS. These products read whole contents of a diskette, they apparently don't interpret the image into a file system (CP/M, FAT13, etc.). The site refers to other programs which do.

ubee512, software to read Microbee diskettes

Stewart Kay is the author of a Microbee emulator for Windows and Linux called ubee512. See my [link to be added] Web page of S-100 Web pointer for specifics. Additional to Stewart's emulator is a Windows/Linux software package to read, write and file-image floppy disks called "ubeedisk". Source, Windows image and Linux image files are available from the MicroBee Software Preservation Project Web site..

Stewart described some attributes of Microbee disk formats and his ubeedisk program to me as follows: "My main interest is to archive Microbee disks which use 10 x 512 byte sectors. Often side one of the disk has the sector headers coded as side 0, also some other strange sector numbering can be used. The Microbee used non-standard GAP values, and fiddled the sync bytes in their native format programs, like some other Microcomputers at the time. So I need software that can cope with this and ImageDisk is able to do that. It also offers other useful diagnostics." He discussed some of its scripting capabilities which support ease of use, and suggests these features and Windows/Linux support provide an alternative to Dunfield's imagedsk.

Also needed for the Windows version, but not supplied with it, is a fdrawcmd.sys driver to access the floppy controller hardware. fdrawcmd.sys can be found at the author's Web site by Simon Owen. (Other diskette utility programs which use this driver are linked from that site as well). Stewart noted his program was written around LibDisk tools and uses the LibDsk library. Consequently it "can produce RAW or CPCEMU DSK and EDSK images or whatever is provided in the LibDsk library. It can read other disk image formats too but not write [them]".

Microcontrollers to replace floppy drives or floppy controllers

This is a discussion I wrote in the 2010's. I also discuss it from a 2020's view, on another Web page.These activities in the 2020's are just outside my interests and abilities to follow, take those notes as opinion and advisory. - Herb.

Since the early 21st century, hobbyists and techs are building "adapters" around inexpensive microcontrollers (Arduino, PIC, Atmel, etc) or inexpensive/hobby "logic analyzers", to operate floppy drives to read (sometimes write) floppy binary data. These generally connect to modern personal computers through USB. Others connect to vintage computer's floppy drive controllers, to operate as floppy drives but store on modern media like SDcards or USB flash-drives.

There are too many of these efforts to track. Some don't stay around long, and they often are limited to one particular vintage-computer interest. They may not provide file-level recovery. It's not my job to represent them or review them; my site documents floppy drives and diskettes for purpose, these are another means to access those. But I can describe how you can find these devices with a Web search, and what you might consider when you do.

Generally these projects are devoted to a single brand or brand product line of vintage computer, like "Heath H8" or "MITS/Pertec". Many have a Web site or are part of an email-based discussion group. Some are individuals who are presenting these as their projects; some are selling them as products. Commonly they 1) archive disk images, generally in a "raw" format; 2) describe and construct hardware tools by which they obtain and use those images on original hardware; and/or 3) offer software tools to use the images in emulators. In some cases, they offer their device as a solid-state floppy drive replacement on specific commercial products: sewing machines or industrial controllers or music synths - at several hundred dollars.

In the 21st century, there's inexpensive logic analyzers made from microcontroller modules and sold for tens of dollars, or available as open-source hobby projects. A logic analyzer samples one or more digital-logic signals, as triggered by other logic events. They are a kind of digital oscilloscope. Various people have added simple logic controls to or with these devices to operate floppy drives (or hard drives!) directly. They force the drive to read tracks; the logic analyzer samples the data stream into a file. Additional software (user written) interprets the binary samples to a raw diskette image; more software extracts sectors; more software interprets sector/track data into files. Here's a Web link to a literal example of use of a generic USB logic analyser module and a USB serial cable to sample and operate a floppy drive. Thanks to Roger Arrick in Jan 2019 for this reference. A Web search on "logic analyser floppy disks" may find current examples and details.

In a number of cases, these support groups or individuals, don't accomodate previously available general purpose vintage-computing tools or disk-images, like Dave Dunfield's IMAGEDSK. In my discussions with such groups, they often can't imagine using "their" disk images or files any other way, execept to provide images for emulators of the original (and specific) computer of interest to them. Unlike the general-purpose methods I've described, there may be no means provided to "extract" individual files from these images which run on Windows/MS-DOS/Linux systems, except by operating their emulators. If the emulator won't install well or if you simply choose not to run it, the alternative is to decode their image formats and to "program" extraction tools yourself.

Eric Smith has some flux-to-image software on his github site. It supports DiskFerret and KyroFlux sampled flux; those are two kinds of floppy-drive thingies. For any given hardware/microcontroller that reads or substitutes for floppy drive/diskettes, someone else generally comes up with software to manipulate the resulting 'data'. The software around the "Catweasel" is a good example.

- Herb Johnson

Catweasel floppy controller

One company which offered a floppy controller of sorts for the PCI bus (and earlier for the ISA bus) was Jens Schönfeld's Individual Computers, in Germany. I cover this specific product because many vintage computer owners used these to analyze diskettes, and to preserve disk image files in that product's binary-sample format. Since mid-2017, the product has not been in production. The 2019 Web site Wiki for Catweasel support was at this link.

They produced at various times in the 1990's and 2000's, the "Catweasel" series of ISA and later PCI-board binary-based floppy controller. This is not a "standard" floppy controller and drives it uses are not available under ordinary MS-DOS, Windows, or Linux "file systems". No "A:> or B:> prompts, no "mount/unmount filesystems". The controller does NOT include a 50-pin connector for 8-inch drives, but people have added such adapters.

This product was initially intended to support Amiga systems by providing a floppy controller and Amiga-type hardware to support Amiga emulation on Windows-type PC's. Other people wrote software to operate it under MS-DOS or Linux, to read other disks and disk formats. Software development for it is scattered among a number of sites and people; I list a few below. A Web search will find other sites, previous and current users of the product, and descriptions what they have done with it.

Many people were or are using these controllers with 8-inch floppy drives, or to read and write 5.25-inch and 3.5-inch Mac and Apple disks, or TRS-80 disks. If you can program, this may be an option for running 8-inch drives with wierd formats on a Windows PC. Some Catweasel cards may be available on the used market. Since late 2004, their cards were PCI based.

for some more Catweasel discussion, check my Web page on using it for very old Intel diskettes.

One software source for TRS-80 and other uses is Tim Mann's TRS-80 pages on the Catweasel. A Web search will find discussion group posts about specific uses and modifications of this software, or sites with more info and software for use. Go to my S-100 pointers page for possible links to other Catweasel sites or software developers. There's several other people who have developed software for use with this card; others over time have added to or adapted their work. There has been a Catweasel discussion group on Yahoo but it's not terribly active.

In Dec 2010, considerable work was done to read old ancient Intel 8-inch M2MF format diskettes which I chronicle on this Web page. Some of those disk images were captured with a Catweasel. Later work was done in 2016-17 upon original Intel Multibus systems.

Programs for the Catweasel named "cwtool" and also "cw", are from Karsten Scheibler's web site. These are parts of a Linux based software package for the Catweasel Mark 4 floppy disk controller. The site has links to providers of other software tools for the Catweasel. The cw and cwtool programs are reported to copy into the image file, the sectors per track in LOGICAL order, not merely copying their PHYSICAL order. Put another way, there is no "interleave" in the image copy.

Herb Johnson
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