last updated April 2002 Contents copyright Herb Johnson Feb 2002. For more info contact hjohnson@pluto.njcc.com Floppy diskettes: media, tracks, bit density, rotation speed, hard sectors To respond to questions reading and writing to diskettes under various combinations of drives and disk media, one needs the technical facts, some knowledge about how diskettes are read and written; and then the actual numbers regarding standards on various floppy media and drives. Tech Notes on floppy drives --------------------------- Diskettes spin at some rotational speed under a read/write head. The head is some distance from the center of rotation so the actual radial speed of the media, and therefore the density of flux changes or bits per radial inch of the media, will vary. The innermost track will have the highest physical density (or lineal density) of bits as the media is moving at the slowest radial speed. Data can be corrupted if the tracks are too close together. Some media support more data density: that media has "higher coerecivity" than media which supports less data density. Data is written by writing a data track with a write head which is followed by a "tunnel erase" pair of heads to erase data on either side of the data track. From manufacturer's notes: The "tunnel erase ceramic type [heads form] non-recorded areas between each track to avoid crosstalk and increase interchangability". And, "when writing, the head erases the outer edges of the track to ensure the data recorded will not exceed the ..track width". Some information below reports the width of the data track before and after the tunnel erase. Numbers on floppy drives and media ---------------------------------- Here are the hot charts for various drives and formats. Some odd but useful facts are also reported. 8-inch drives, 77 tracks: track bit density, innermost track 3200-3600 bpi for single density, 6400-6500 bpi for double density (note: index hole in sleeve in different locations for single/double sided) rotation speed 360 RPM track density 48 tpi (tracks per inch) track width: .012 inches track interval (implied): .0208 inches data frequency 250Kbps, FM single density 500Kbps, MFM double density write current reduced when writing to tracks > 43 media: iron oxide coating, 300 oresteds coercivity all formats sleeve material: dilithium/paper matrix 5.25 inch drives, 40 track track bit density, innermost track 2500-2900 bpi for single density, 5600-5900 bpi for double density rotation speed 300 RPM track density 48 tpi (tracks per inch) head stepper motor angle per step: 3.6 degrees capacity 250KB single density (less formatted) 500KB single density less formatted) track radius from 1.542 inches to 2.250 inches (maybe 35 track?) 1.354 inches to 2.25 inches Track width before tunnel erase .013 inch after erase .0124 inch (.012, .33mm [.0129 inch] also reported) Track interval .0208 inches media: iron oxide coating, 300 oresteds coercivity 5.25 inch drives, 80 track track bit density, innermost track 3000 bpi for single density FM 6000 bpi for double density MFM rotation speed 300 RPM track density 96 tpi (tracks per inch) (some drives 100 tpi) head step angle 1.8 degrees capacity 500KB single density (less formatted) 1MB double density (less formatted) data frequency 125Kbps, FM single density 250Kbps, MFM double density track radius ??? (probably similar to 40 track drives?) Track width before tunnel erase .0065 inch after erase "to not exceed .006 inch". Track interval (implied): .0104 inches media: iron oxide coating, 300 oresteds coercivity 5.25 inch drives, 1.2M, 80 track track bit density, innermost track 9600-9800 bpi for double density MFM rotation speed 360 RPM track density 96 tpi (tracks per inch) (some drives 100 tpi) head step angle 1.8 degrees Track width: .16 mm (.0063 inch), also .0061 inch media: cobalt coating, 600 oresteds coercivity 3.5 inch drives, 720K and 1.44M and 2.88M rotation speed: 300 RPM track density 134, 135 tpi 80 tracks per side; IBM MS-DOS sectors per track 9, 18, 36 respectively head step angle 1.8 degrees track bit density: 8717 bpi at 720K; 17,434 bpi at 1.44M; 34,848 at 2.88M media: cobalt, 665 Oersteds at 720K; 720 Oresteds at 1.44M; barium, 1200 at 2.88M track width: .115 mm (.0045 inch) Facts on hard sectored diskettes and "drives" 1) Hard sector means that the DISKETTE (not the drive) has multiple holes, one for each sector. Normal (soft sectored) diskettes have only ONE hole to mark the "index" or beginning of a track. There is a small hole in the envelope (8-inch, 5.25-inch) which exposes this hole to the disk drive. For hard sectored disks, there are additional holes to mark the beginning of each sector. The index hole is an additional hole between two sector holes. 2) 5.25 inch hard sector diskettes come in 10 sector (11 holes) and 16 sector (17 holes). To count holes, grab a diskette. Rotate the "doughnut" inside the diskette's envelope and count the holes. Remember the index hole is in between two sector holes (smaller spacing). For 8-inch diskettes, they come in 32 sectors (33 holes). (But let me know if there were even more options!). 3) Hard sectoring is an attribute of DISKETTES, NOT DISK DRIVES! However there were some 8-inch drives (Shugart 800 and 801) which provided circuitry to generate hard sector pulses from soft sectored diskettes. (Or was that to filter hard sector pulses OUT from hard sectored diskettes? Check with the Shugart 800/801 manual, or let me know, or ask ME to check the manual!) Copyright 2002 Herb Johnson. Not responsible for errors or omissions, any corrections appreciated but please give references too! Sources: Shugart SA-400, SA-410, SA-460 manuals Tandon TM100-1, -2, -3, -4 manuals Canon MDD-210, -220 manuals Calcomp 140, 142, 143 manuals CDC, MPI BR80 manuals http://www.advancement.cnet.navy.mil/products/web-pdf/tramans/bookchunks/14100_ch10.pdf Navy training manual: Fire Controlman, Volume 03 - Digital Data Systems, NRTC 14100. Chapter 10. (Public distribution) http://www.tvdsb.on.ca/banting/cicp/hardware/PCGuide/ref/fdd/const-c.html Floppy Disk Drive Construction and Operation - PC Guide, Disk Edition Data obtained under "fair use" doctrine. http://mitsumi-components.com/ mitsumi floppy disk manuals on-line, 3.5" drives "3M Diskette Reference Manual" of 15 February 1990, courtesy Don Maslin