8-inch HD high-density diskettes

Last updated Sept 27 2023. Edited by Herb Johnson, (c) Herb Johnson, except for content written by others. Contact Herb at www.retrotechnology.com, an email address is on that page..




In October-November 2017, colleagues of mine at work on Intel Multibus systems, came across sets of 8-inch floppy disks, I never imagined existed. Produced by Maxell (Hitachi in Japan), these are high density 8-inch diskettes, for 96 track-per-inch 8-inch drives! It says so on the box! My friends tried to work with these disks but had multiple problems for use with "ordinary" 8-inch floppy drives and controllers. It took some time to realize how "odd" these were. Thanks to Jack McMullen for his technical review of these diskettes, and his efforts to format them on an ordinary 8-inch floppy drive. Also thanks to ?? for more information.


Summary: 8-inch floppy diskettes are typically single or double density (FM, MFM, M2FM) and are coated with some form of iron oxide. 8-inch drives typically have 76 tracks at 48 tracks per inch (TPI). Apparently Maxell/Hitachi had a customer, who needed more data per diskette. They achieved that, by doubling the number of tracks to 96 TPI. They also increased recording density to "high density", apparently with the same media coating as used on 5.25-inch 1.2Mb "high density" diskettes. The location of the index hole was changed to the LEFT of center (not right as in SS or DS diskettes) to recognize only HD diskettes in HD drives and not in conventional drives. But the index hole in the media, is at the same radius as other 8" media.

8-inch HD specifications:
8-inch diameter media and 8 X 8 envelope like other 8" media
high-density coating like Maxell's 5.25" HD diskettes
designed for 96 TPI 8" drive, probably 154 tracks!
index hole radius 1.5" from center like other 8" media
index hole at 17 degrees counter-clockwise, different from single or double-density, see notes below
index hole 5-7/16" from the insert edge, 3-9/16" from the LEFT hand side edge
likely use of disks in Japanese market


tracks per inch: At the top of this Web page, you can see photos of the diskette box and one of the diskettes. A closeup of the diskette label confirms the features of "high density" and "96 TPI", as well as a preformatted sector size of 256 bytes.



Market for use: Examination of the top of the box shows Japanese writing. The label on the Maxell sleeve provides a Japanese address in English and Japanese. That suggests where these were marketed, and likely produced.


coating: By visual inspection I confirm the media is high-density. I found a Maxell 5.25" HD diskette. Compare the look of the 8-inch vs. 5.25-inch coatings through the "windows" where the head accesses the media; and at the center hub. The colors look different due to reflection. But colors at the hub or at the head, are the same between the two diskettes. I've not found reference to the coating used for either Maxell diskette.

formatting: This information provided by Joe Duszynski in Sept 2019.

"This info is based on our Hitachi system. The HD 8" Floppy drive was used to backup the hard disk DK511 on a half dozen 8" HD floppies. This floppy drive hooks up to a hard disk controller, Recording Modulation RLL C 2,7 Data Transfer MFM."

Unformatted Disk capacity 9.6M
Formatted 6.15M (78 sect 256k, 154 tracks per side)
The Maxell FD2-HD 8" media came in three types, FD2-HD, FD2-256D and FD2-1024D

".. and you could ONLY get them from MAXELL/HITACHI. The 256 and 1024 were preformatted."

Rotation 360 RPM
Flux Reversal Per Inch 13,700 FRPI
Recording density 20,560 BPI
Track Density 96 TPI
Access time (including settling) Track 39ms, Average of all Tracks 140ms

"This is all from my notes as the original book was in Japanese. I had my neighbor translate it when we got the machine way back in the late 80's." - Joe

index hole mesurement

This will be a busy measurement, and not precise but close.

Standard 8-inch index holes are described in a 3M Diskette Reference manual I obtained from bitsavers.org. "the index hole for [8-inch] SS diskettes...is approximately 7 degrees" [clockwise]. "the index hole for DS diskettes ...is approximately 26 degrees" [clockwise]. Inspection of the 8-inch HD diskette shows it's clearly COUNTER-clockwise.

Measuring SS, DS and HD diskettes, I get these rough results:

Single-sided: 5-1/2" from the edge you first insert into the drive. (5.50)
3-3/4" from the right hand side edge. (3.750)

Double-sided: 5-5/16" from the insert edge. (5.3125)
3-5/16" from the right hand side edge. (3.3125)

High-density: 5-7/16" from the insert edge. (5.4375)
3-9/16" from the LEFT hand side edge. (3.5625)

Radius of index hole: A did a direct comparison of an 8" single-sided diskette to the 8" HD diskette, with index holes of both media visible. I aligned the two hub-holes of the media, and also the index holes in both jackets and media. Result: the index holes in the media overlapped. That means the radius of the index holes is the same. This makes sense: the Mylar "cookie" for both disks is physically the same, with the same center-hub size and index hole radius.

index hole angle: To convert to angles without a protractor, is a matter of the tangent angle, relative to the center of the hub. The diskettes are 8 inches in diameter. So for single-sided, the right triangle is .25 inch / 1.5 inch or arctan(.375)= 9.46 degrees. For double-sided, the triangle is 11/16 = .6875 / 1-5/16=1.3125 or arctan(0.524) = 27.6 degrees. These are pretty close, as a sanity check.

So, for the HD disk, the triangle is 7/16=.4375 / 1-7/16=1.4375 or arctan(.3043) = 16.9 degrees. Also, a rough protractor reading, looks around 17 degrees; again to the left or counter-clockwise. That puts the index sensor "between" SS and DS diskettes. That matters, because if you insert the HD diskette upside-down into a SS or DS drive, it won't be detected via the index-hole sensors. Same with either SS or DS diskettes, into a HD drive.

Contact information:
Herb Johnson
New Jersey, USA
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This page and edited content is copyright Herb Johnson (c) 2023. Copyright of other contents beyond brief quotes, is held by those authors. Contact Herb at www.retrotechnology.com, an email address is available on that page..