Last edit May 6 2022. Original content here (c) copyright 2022 Herb Johnson, except content which is owned by its authors.
When the 3.5 inch floppy disk and drive were introduced by Sony, there was an alternative 3-inch sized disk and drive as produced by other manufacturers. For a time both were in play, until the 3.5 inch scheme won out. This Web page discusses those 3 inch media and drives and how were they were put to use. Thanks to Alan Cox, who permitted me to publish his correspondence about those drives, which started this Web page. My slight edits are in 's. Thanks to others as named, who provided more information about these drives and products. - Herb Johnson
The floppy disk image to the left, shows a stylised "CF" brand and the letters "Compact Floppy Disk". Apparently "CF-2" was a standard for the 3-inch diskette format for mutual physical media compatibility.
Alan Cox, 24 Apr 2020: Your rather amazing floppy faq says, "Apparently 3.0 inch diskettes were a serious alternative proposal to the 3.5 inch diskette". That [circumstance] was a Japanese format war. Sony 3.5" format, versus Matsushita/Hitachi and a few others pushing a 3" format called CF-2. Sony won as pretty much only Amstrad and Sega adopted CF-2.
In the United Kingdom, Amstrad backed the 3" format and got very nice sweetener deals and guarantees of availability; and so shipped millions of systems with them. So 3" disks were quite common over here. In fact pre-Atari ST/Amiga/PC, they were probably the most common [format.] More UK CP/M systems shipped with 3" than anything else, owing to the Amstrad PCW series.
720K Amstrad drive photos by Alan Cox. Alan says: [There were] two different kinds of drives:
180K (40 track, single sided double density, 512 byte sectors, 9 sectors per track). [Single sided] disks can be flipped by design to use each side;
720K (80 track, double sided, double density, 512 byte sectors, 9 sectors per track), disks cannot be flipped (or rather they can but it's not useful as almost all the tracks overlap).
Usually the drives were 12ms step, 30ms head settle, 2/1 interleave [on sector format].
The other oddity was the connector. They used a 26 pin connector and a power connector that was physically but not electrically compatible with the 3.5" floppy one. Plug a 3.5" power connector into one and it will go bang! . Beyond that issue, and sometimes having to fiddle with the step rate, they work with all the standard controller chips that do 3.5".
Both the disks and the drives are practically bullet proof, the drives
had a band drive for the motor which went but the band is easily
"The disks do have a sliding door, it's actuated by a plastic link embedded in the side of the disk with the metal door housed internally in the disk itself." [I don't know if this was true for both single and double-sided diskettes. - Herb]
"The [Amstrad 3 inch disk drives use] double sided flippy [disks] but none of the Amstrad CPC drives (664 or 6128) were double sided. They MAY have changed that with some of the PCW8512 machines and PC clones later, but the early drives were only single sided. These disks were also used with the ZX Spectrum +3 machines after Sinclair was purchased by Amstrad. Also the Spectrum +2 had the same built in tape drive as the Amstrad CPC464."
"I have loads of these things in the workshop. The disks are so much more robust than either the 5 1/4" floppy floppies or the [now-]standard 3.5" disks. You can barely bend 3" disks as the cases are very strong." - Colin Day
The machines shipped with those Amstrad drives included [the following:]
Sinclair ZX Spectrum +3 (1 x 180K drive built in). Disk format was CP/M but handled by the system ROM and usable from basic and assembler. CP/M itself was a paid add on.
Amstrad CPC DDI-1 (external disk for Amstrad CPC series machines, 180K)
Amstrad CPC6128 (180K drive built in, same format as ZX Spectrum, CP/M available)
Amstrad PCW series machines. Early machines shipped with a single 180K drive, later ones with a 180K A: and 720K B: drive. They were originally designed around a wordprocessor app, but shipped with both that and CP/M 3. Almost all of them shipped with 3" disks, the final versions switched to 3.5" but by then the market for them was already dying.
Amstrad sold around 8 million PCW series machines into the UK, Germany and Netherlands, about a million disk enabled Amstrad CPC systems, and about half a million Spectrum +3 models. The PCW was (until the early PC systems killed it), the primary small business system in the UK.
The cpcwiki.eu Web site has a fair bit of info, offering The DDI-1 drive service manual; and much the same info in the Amstrad PCW system service manual.
specifications for Teac FD-30A (from data sheet) single sided 82K 40 track single density single sided 164K 40 track double density 16 sectors 128/256 bytes per track - but usable as MS-DOS SS DD disk & format rotation speed 300RPM 100 TPI, 4473 or 8946 BPI
From Nick Button, June 2021: "I acquired this Teac FD-30A drive 30 years ago. The drive was apparently used in the Tatung Einstein computer. I've only ever used it with an Acorn BBC model B, then latterly with a 386SX single-board computer, where it behaves like a normal 40-track single sided drive. [Including a 34-pin edge connector
as in this photo.] It uses the same 3" disks as the Amstrad drives which can be flopped over to give two 40-track single-sided images, although from what I have seen of the Amstrad drive mechanisms, this one appears to have been built to a higher standard." - Nick
Timex/Sinclair, who produced the 2068 and ZX Spectrum, apparently had a division Timex Portugal who produceed a 3-inch floppy drive system called the FDD 3. This system used a 3-inch single-sided floppy drive, the Hitachi HFD305S. These FDD 3 products were imported into the USA by a few distributors.
Web search found the Oric computer also used the HFD305S drive. The Oric was produced in the 1980's into the early 1990's, produced and supported by companies in the UK and France; it had a troubled history during the very competative home small/game computing era.
A manual for the HItachi drive was found on the Internet Archive, from which I snipped this photo.
It's a 100TPI drive, 40 tracks, 300 RPM; supporting reversable diskettes. It appears to use a 34-pin edge connector with signals
consistent with 3.5 and 5.25 inch drives. Hitachi advertized this '3" Compact Floppy Disk Drive' in Byte of June 1983, noting
"disks marked with the [CF symbol] can be used with this drive." (Thanks to Jacek Trojanski for calling this drive to my attention.)
Copyright © 2022 Herb Johnson