Editing Group coded recording (section)

== References ==
{{Reflist|refs=
<ref name=X3.54>{{cite tech report
 |title=FIPS PUB 50/ANSI X3.54-1976: Recorded Magnetic Tape for Information Interchange (6250 CPI, Group-Coded Recording)
 |type=American National Standard
 |url=https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub50.pdf
 |year=1976
 |publisher=[[ANSI]]
 |access-date=2024-07-19
}}</ref>
<ref name="Savard_2006">{{cite web |title=Digital Magnetic Tape Recording |author-first=John J. G. |author-last=Savard |date=2018 |orig-year=2006 |work=quadibloc |url=http://www.quadibloc.com/comp/tapeint.htm |access-date=2018-07-16 |url-status=live |archive-url=https://web.archive.org/web/20180702234956/http://www.quadibloc.com/comp/tapeint.htm |archive-date=2018-07-02}}</ref>
<ref name="Patel_1988_MR">{{cite book |title=Magnetic Recording |chapter=5. Signal and Error-Control Coding |author-last=Patel |author-first=Arvind Motibhai |editor-last1=Mee |editor-first1=C. Denis |editor-last2=Daniel |editor-first2=Eric D. |publisher=[[McGraw-Hill Book Company]] |date=1988 |volume=II: Computer Data Storage |edition=1st |isbn=0-07-041272-3 }}</ref>
<ref name="Harris_1981_IBM">{{cite journal |title=Innovations in the Design of Magnetic Tape Subsystems |author-first1=John P. |author-last1=Harris |author-first2=William B. |author-last2=Phillips |author-first3=Jack F. |author-last3=Wells |author-first4=Wayne D. |author-last4=Winger |journal=[[IBM Journal of Research and Development]] |volume=25 |number=5 |date=September 1981 |publisher=[[International Business Machines Corporation]] |pages=691–700 |doi=10.1147/rd.255.0691 |citeseerx=10.1.1.83.2700}}</ref>
<ref name="CW_1973_IBM">{{cite journal |author=CW staff |title=6,250 Byte/In. Density – IBM 3420 Storage More Than Tripled |journal=[[Computerworld]] |location=White Plains, New York, USA |pages=1–2 |date=1973-03-14 |volume=VII |issue=11 |url=https://books.google.com/books?id=11t5CuO-UfUC&pg=PP1 |access-date=2017-03-23  |quote=[[IBM]] added three new models to the [[IBM 3420|3420]] magnetic tape system than can record data at the "densest recording capability yet offered", according to the company. Using a new method called [[Group Coded Recording]] (GCR), the IBM drives can handle tapes containing a data density of 6,250 byte/in. compared with 1,600 byte/in. on earlier models of the 3420. [...] An upgraded control unit was also announced – the [[IBM 3803|3803]] Model 2 – which operates with both the earlier and latest 3420 tape units. The Model 2 includes the capability of correcting errors in one or two tracks "simultaneously while the tape is in motion", IBM said. [...] The GCR method segments data written on tape into groups of characters to which a special coding character is added. And the higher density is based on a combination of a modified coding scheme, a smaller interrecord gap (called an interblock gap) and modified electronics and electromechanical components, IBM said. Installed 3803/3420 tape systems can be converted to the higher densities in the field. [...]}}</ref>
<ref name="OldIron_2004_IBM3803">{{cite web |title=The Gallery of Old Iron |date=2004 |url=http://www.thegalleryofoldiron.com/3803.HTM |url-status=dead |archive-url=https://web.archive.org/web/20081225092106/http://www.thegalleryofoldiron.com/3803.HTM |archive-date=2008-12-25 |quote=[...]<!-- I was the Lead Designer and Architect of the 3803. I started with IBM in 1956 as a CE trainee on the 705 Model II; we installed 2 705s in Nashville, TN in 1957, one at National Life and Accident and one at General Shoe. --> I moved to the lab at Poughkeepsie in 1958 [...]<!-- and worked on the 705 Model III and the Tractor and Swift tape drive projects. Swift became Hypertape and I was Lead designer of the Hypertape control unit. --> I later was Lead designer and architect for the [[IBM 2802|2802]] Tape Control Unit and a few years after that, Lead Designer and Architect of the [[IBM 3803|3803]] which was a very large modification based on the 2802. Three of us shared a Corporate Award for the 3803 and I, along with Planner Charlie Von Reyn, came up with the name "[[Group Coded Recording]] (GCR)" as the name of the recording method. [...]<!-- The 3803 was so much in demand even after production ceased that we put competitors tape systems in our own data center so that we could recondition the 3803s and 3420s and ship them to customers. I retired in 1991 as a Senior Engineer with 30 filed patents, at least 29 of which issued. -->}} (NB. An anonymous comment by one of the developers on the origin of the name "Group Coded Recording".)</ref>
<ref name="Patel_1974_ORC">{{cite journal |author-last1=Patel |author-first1=Arvind Motibhai |author-last2=Hong |author-first2=Se June |title=Optimal Rectangular Code for High Density Magnetic Tapes |journal=[[IBM Journal of Research and Development]] |volume=18 |issue=6 |pages=579–588 |date=1974 |doi=10.1147/rd.186.0579 |url=https://domino.research.ibm.com/tchjr/journalindex.nsf/a3807c5b4823c53f85256561006324be/f27484e80210353385256bfa0067f987!OpenDocument |access-date=2017-03-21  |archive-date=2017-11-04  |archive-url=https://web.archive.org/web/20171104194300/https://domino.research.ibm.com/tchjr/journalindex.nsf/a3807c5b4823c53f85256561006324be/f27484e80210353385256bfa0067f987!OpenDocument |url-status=dead |url-access=subscription }}</ref>
<ref name="Allen_1978_Byte">{{cite journal |title=A Minifloppy Interface |author-first=David |author-last=Allen |location=Kansas City, USA |journal=[[BYTE]] |date=February 1978 |volume=3 |number=2 |pages=114, 116–118, 120, 122, 134–125 |url=http://www.rsp-italy.it/IT/Magazines/Byte/_contents/BYTE%20Vol%2003-02%201978-Feb%20-%20Hardware%20Projects.pdf |access-date=2017-06-14 |archive-url=https://web.archive.org/web/20170614002927/http://www.rsp-italy.it/IT/Magazines/Byte/_contents/BYTE%20Vol%2003-02%201978-Feb%20-%20Hardware%20Projects.pdf |archive-date=2017-06-14 |quote=[...] Of the alternative codes used to achieve double density, GCR (Group Coded Recording) looks quite attractive. Micro Peripherals Inc has implemented double density using GCR in a full size floppy disk and controller system currently being marketed. [...] GCR is nothing more than the old standby NRZ with its attendant advantages, but, since ordinary NRZ has no clocking information and a potentially high DC content during long strings of ones or zeros, the data is reformatted to eliminate the long strings. The reformatting converts each four bit group of original data into five bits of group coded data; the five bits in the encoded version will always have a mix of ones and zeros, even if the real data is all in one state. Reformatting in GCR can be accomplished in software, as opposed to MFM, etc, which almost unavoidably must be encoded and decoded in hardware. Thus, GCR has good possibilities as a low cost, high reliability scheme for achieving double density. [...]}}[http://www.americanradiohistory.com/Archive-Byte/70s/Byte-1978-02.pdf]</ref>
<ref name="Schultz_1978_Durango">{{cite journal |url=https://books.google.com/books?id=QmEH10OiXZkC&pg=PA4 |title=Business Mini Weighs 65 Pound – What is Durango? |author-first=Brad |author-last=Schultz |pages=1, 4 |journal=[[Computerworld]] |publisher=[[CW Communications, Inc.]] |volume=XII |number=40 |date=1978-10-02 |access-date=2017-06-13}}</ref>
<ref name="CW_1979_MPI">{{cite journal |title=Floppies Claim Improved Performance |journal=[[Computerworld]] |publisher=[[CW Communications, Inc.]] |date=1979-02-12 |volume=XIII |number=7 |page=90 |url=https://books.google.com/books?id=sglMaWvdPEUC&pg=RA1-PA90 |access-date=2017-06-14}}</ref>
<ref name="Watkinson_1990">{{cite book |title=Coding for Digital Recording |chapter=3.4. Group codes |author-first=John |author-last=Watkinson |publisher=[[Focal Press]] |location=Stoneham, MA, USA |date=1990 |isbn=0-240-51293-6 |pages=51–61}}</ref>
<ref name="Feichtinger_1987">{{cite book |author-first=Herwig |author-last=Feichtinger |title=Arbeitsbuch Mikrocomputer |language=de |location=Munich, Germany |publisher=[[Franzis-Verlag GmbH]] |isbn=3-7723-8022-0 |date=1987 |edition=2 |pages=223–224}}</ref>
<ref name="Sirius1_Specs">{{cite web |title=Victor 9000/Sirius 1 Specification |url=http://www.commodore.ca/history/people/chuck_peddle/Sirius_1_Victor_9000_Specification.pdf |publisher=commodore.ca |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323230447/http://www.commodore.ca/history/people/chuck_peddle/Sirius_1_Victor_9000_Specification.pdf |archive-date=2017-03-23}}</ref>
<ref name="Victor_1983_Technical_Reference">{{cite web |title=Supplemental Technical Reference Material |id=Application Note: 002 |publisher=[[Victor Publications]] |location=Scotts Valley, CA, USA |date=1983-03-23 |edition=1st printing |version=Revision 0 |url=https://archive.org/stream/bitsavers_victorvict83_1876736/appNote002_Mar83#page/n0/mode/1up |quote=[...] Single-sided floppy drive offers 80&nbsp;tracks at [[96&nbsp;tpi|96 TPI]] [...] Double-sided floppy drive offers 160 tracks at 96&nbsp;TPI [...] Floppy drives have 512&nbsp;byte sectors; utilising a GCR, 10-bit recording technique. [...] Although the [[Victor 9000]] uses 5&nbsp;1/4-inch minifloppies of a similar type to those used in other computers, the floppy disks themselves are not readable on other machines, nor can the Victor 9000 read a disk from another manufacturers machine. The Victor 9000 uses a unique recording method to allow the data to be packed as densely as 600&nbsp;kbytes on a single-sided single-density minifloppy; this recording method involves the regulation of the speed at which the floppy rotates, explaining the fact that the noise from the drive sometimes changes frequency.}}</ref>
<ref name="Victor_1982_Technical_Reference">{{cite book |title=Victor 9000 Technical Reference Manual |chapter=Chapter 7. Disk Drive Assembly |date=June 1982 |publisher=[[Victor Business Products, Inc.]] |id=710620 |pages=7–1..7–9 |url=https://www.mirrorservice.org/sites/www.bitsavers.org/pdf/victor/victor9000/Victor9000TechRef_Jun82.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323232847/https://www.mirrorservice.org/sites/www.bitsavers.org/pdf/victor/victor9000/Victor9000TechRef_Jun82.pdf |archive-date=2017-03-23 |quote=[...] Track density is 96 tracks per inch, and recording density is maintained at approximately 8000 bits per inch on all tracks. [...] The [[Victor 9000|VICTOR 9000]] uses an encoding technique called group code recording (GCR) to convert the data from internal representation to an acceptable form. GCR converts each (4-bit) nibble into a 5-bit code that guarantees a recording pattern that never has more than two zeros together. Then data is recorded on the disk by causing a flux reversal for each "one" bit and no flux reversal for each "zero" bit. [...]}}</ref>
<ref name="Sharp_1986_CE1600F">{{cite book |title=Sharp PC-1600 Service Manual |chapter=Model CE-1600F |pages=98–104 |date=July 1986 |publisher=[[Sharp Corporation]], Information Systems Group, Quality & Reliability Control Center |location=Yamatokoriyama, Japan |url=http://sharppocketcomputers.com/4HK7JnFJDuVm/Service/ce1600f_service_manual.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170507223047/http://sharppocketcomputers.com/4HK7JnFJDuVm/Service/ce1600f_service_manual.pdf |archive-date=2017-05-07 |quote=GCR is an abbreviation of [[Group Coded Recording]]. A single byte, 8 bits, data are divided into two 4-bit data which is also converted onto a 5-bit data. Thus, a single byte (8 bits) is recorded on the media as a 10-bit data.}}</ref>
<ref name="Sharp_1986_CE140F">{{cite book |title=Sharp Service Manual Model CE-140F Pocket Disk Drive |publisher=[[Sharp Corporation]] |id=00ZCE140F/SME |url=http://pockemul.free.fr/Documents/ce-140f_Service_manual.pdf |access-date=2017-03-11 |url-status=live |archive-url=https://web.archive.org/web/20170311145818/http://pockemul.free.fr/Documents/ce-140f_Service_manual.pdf |archive-date=2017-03-11}}</ref>
<ref name="Lechner_1982_Beneath_Apple_DOS">{{cite book |author-last2=Lechner |author-first2=Pieter M. |author-last1=Worth |author-first1=Don D. |title=Beneath Apple DOS |date=May 1982 |orig-year=1981 |edition=4th printing |publisher=[[Quality Software]] |location=Reseda, CA, USA |url=https://archive.org/stream/Beneath_Apple_DOS_OCR#page/n24/mode/1up |access-date=2017-03-21 }} [http://asciiexpress.net/files/docs/Beneath%20Apple%20DOS%20OCR.pdf<!-- https://web.archive.org/web/20170320233805/http://asciiexpress.net/files/docs/Beneath%20Apple%20DOS%20OCR.pdf -->] [https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/Beneath%20Apple%20DOS.pdf] [http://fd.fabiensanglard.net/prince_of_persia/Beneath%20Apple%20DOS.pdf] {{Webarchive|url=https://web.archive.org/web/20160309202219/http://fd.fabiensanglard.net/prince_of_persia/Beneath%20Apple%20DOS.pdf |date=9 March 2016 }}</ref>
<ref name="Lechner_1985_Beneath_Apple_ProDOS">{{cite book |author-last2=Lechner |author-first2=Pieter M. |author-last1=Worth |author-first1=Don D. |title=Beneath Apple ProDOS – For Users of Apple II Plus, Apple IIe and Apple IIc Computers |date=March 1985 |orig-year=1984 |edition=2nd printing |publisher=[[Quality Software]] |location=Chatsworth, CA, USA |isbn=0-912985-05-4 |lccn=84-61383 |url=http://www.apple-iigs.info/doc/fichiers/beneathprodos.pdf |access-date=2017-03-21 |url-status=live |archive-url=https://web.archive.org/web/20170321014045/http://www.apple-iigs.info/doc/fichiers/beneathprodos.pdf |archive-date=2017-03-21}} [https://archive.org/details/A2_BENEATH_APPLE_PRODOS_1_1984]</ref>
<ref name="Sather_1983_Understanding_Apple_II">{{cite book |author-last=Sather |author-first=James<!-- Jim --> Fielding |title=Understanding the Apple II – A Learning Guide and Hardware Manual for the Apple II Computer |date=1983 |edition=1st |publisher=[[Quality Software]] |location=Chatsworth, CA, USA |isbn=0-912985-01-1 |pages=[https://archive.org/details/Understanding_the_Apple_II_1983_Quality_Software/page/9 9–26, 9–27] |url=https://archive.org/details/Understanding_the_Apple_II_1983_Quality_Software/page/9 |access-date=2017-03-21 }}</ref>
<ref name="CP_1989_CopyII">{{cite book |title=Copy II Plus Version 9 – ProDOS/DOS Utilities – Data Recovery, File Management, Protected Software Backup |publisher=[[Central Point Software, Inc.]] |version=9.0 |date=1989-10-31 |orig-year=1982 |url=http://cps.applearchives.com/copy_ii_plus_9x_manual.pdf |access-date=2017-03-21 |archive-url=https://archive.today/20170507224326/http://cps.applearchives.com/copy_ii_plus_9x_manual.pdf |archive-date=7 May 2017 |url-status=dead }}</ref>
<ref name="Williams_1985_Byte">{{cite journal |title=The Apple Story / Part 2: More History and the Apple III |journal=[[BYTE]] |date=January 1985 |author-last1=Williams |author-first1=Gregg |author-last2=Moore |author-first2=Rob |page=166 |type=interview |url=http://apple2history.org/museum/articles/byte8501/ |access-date=2013-10-26 |url-status=dead |archive-url=https://web.archive.org/web/20120212185115/http://apple2history.org/museum/articles/byte8501/ |archive-date=2012-02-12}} [https://archive.org/stream/byte-magazine-1985-01/1985_01_BYTE_10-01_Through_the_Hourglass#page/n167/mode/2up] (NB. Interview with [[Steve Wozniak]], where he describes creating the [[Apple Computer|Apple]] version of GCR.)</ref>
<ref name="Hendrie_2003_Comstock">{{cite web |title=Oral History of George Comstock |location=Mountain View, California, USA |author-first=George E. |author-last=Comstock |interviewer-first=Gardner |interviewer-last=Hendrie |date=2003-08-13 |id=CHM X2727.2004 |publisher=[[Computer History Museum]] |url=http://archive.computerhistory.org/resources/text/Oral_History/Comstock_George/Comstock_George_1.oral_history.102658008.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323110042/http://archive.computerhistory.org/resources/text/Oral_History/Comstock_George/Comstock_George_1.oral_history.102658008.pdf |archive-date=2017-03-23}}</ref>
<ref name="Guzis_2015_Multi">{{cite web |title=Multi-platform distribution format |author-first=Charles "Chuck" P. |author-last=Guzis |date=2015-09-20 |publisher=Sydex |url=https://www.mail-archive.com/search?l=cctalk@classiccmp.org&q=subject:%22Re%5C%3A+Multi%5C-platform+distribution+format+%5C(Was%5C%3A+Backups+%5C%5Bwas%22&o=newest&f=1 |access-date=2017-06-14 |url-status=live |archive-url=https://web.archive.org/web/20170614234505/https://www.mail-archive.com/search?l=cctalk@classiccmp.org&q=subject:%22Re%5C%3A+Multi%5C-platform+distribution+format+%5C(Was%5C%3A+Backups+%5C%5Bwas%22&o=newest&f=1 |archive-date=2017-06-14 |quote=[...] At the same time Micropolis was working a 5.25" drive that could hold about as much as an 8", using some tricks. The Micropolis drive was 100 tpi, 77 track and, by using GCR, could hold 12 512-byte sectors per track. That's 462&nbsp;KiB. This was about 1977–78. [...] The [...] drive and controller implementation (ours was done by a guy we'd recruited from Sperry ISS) was [...] complex and expensive [...] Brother WP disks [...] are 38 track, single-sided, Brother-encoded GCR that hold [...] 120K on 2D floppies. [...]}}</ref>
<ref name="Guzis_2006_F85">{{cite web |title=The Durango F-85 Computer |author-first=Charles "Chuck" P. |author-last=Guzis |date=October 2006 |publisher=Sydex |url=http://www.sydex.com/durango/durango.html |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323113240/http://www.sydex.com/durango/durango.html |archive-date=2017-03-23}}</ref>
<ref name="Durango_800">{{cite web |title=800 Technical Summary – 800 Series Business Computer System |publisher=[[Durango Systems, Inc.]] |location=San Jose, CA, USA |url=http://www.sydex.com/durango/durango.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323112022/http://www.sydex.com/durango/durango.pdf |archive-date=2017-03-23}}</ref>
<ref name="Micropolis_1978">{{cite journal |title=NCC Preview: OEMs at NCC – Micropolis Corp. |journal=[[Computerworld]] |publisher=[[CW Communications, Inc.]] |volume=XII |number=22 |date=1978-05-28 |page=P/50 |url=https://books.google.com/books?id=Qrjca3MN6nIC&pg=PT66 |access-date=2017-06-12 |quote=[...] [[Micropolis Corporation|Micropolis]] has extended the capacity of 5.25-in. floppy disk subsystems via double-sided models with formatted file storage of up to nearly 2 million bytes [...] The [[Megafloppy]] series also features an intelligent controller that facilitates interconnection of four subsystems to a common host interface for a total [[on-line storage capacity]] of more than 15M bytes [...] Double-sided versions of the product line will be implemented first in two [[Original equipment manufacturer|OEM]] series – Model 1015 and Model 1055 [...] The Model 1015 is an unpackaged drive designed for the manufacturer who integrates floppy disk storage into his own system enclosure. A range of storage capacities from 143,000 to 630,000 bytes per drive is available [...] Model 1015 customers have the option of using the Micropolis intelligent controller and [[Group Code Recording]] (GCR) method to further expand file space up to 946,000 bytes [...] Offering GCR and a microprocessor-based controller as standard features, the Model 1055 5.25-in. floppy has four [[soft-sectored]] formats for each of its 77 tracks, yielding a maximum capacity of 1,892,000 bytes of file space on its double-sided version [...] An add-on module available for the 1055 is {{sic|comprised |hide=y|of}} two read/write heads and two drives, sharing a common controller. The subsystem capacity (formatted) with the module is 3,784,000 bytes [...] Up to four 1055s, each with an add-on module, can be [[daisy chain (electrical engineering)|daisy-chained]] to a common host for a maximum on-line storage capacity of more than 15M bytes [...]}}</ref>
<ref name="Jacoby_1977_3PM">{{cite journal |author-first=George V. |author-last=Jacoby |location=[[Sperry Univac]], ISS Division, Cupertino, CA, USA |title=A new look-ahead code for increased data density |journal=[[IEEE Transactions on Magnetics]] |volume=13 |issue=5 |date=2003-01-06 |orig-year=September 1977 |pages=1202–1204 |doi=10.1109/TMAG.1977.1059670 |publisher=[[IEEE]]}} (NB. This article about the [[3PM (code)|3PM]] code was also presented at the [[Intermag]] 1977 in June 1977.)</ref>
<ref name="McClelland_1979_GCR">{{cite patent |title=Compatible Digital Magnetic Recording System |country=US |number=4261019 |pubdate=1981-04-07 |fdate=1979-11-29 |pridate=1979-11-29 |inventor-first=S. Barry |inventor-last=McClelland |assign1=[[Micropolis Corporation]]}} (NB. Application Number: US 06/098381)</ref>
<ref name="Hildon_1985_Anthology">{{cite book |author-last=Hildon |author-first=Karl J. H. |title=The Complete Commodore Inner Space Anthology |chapter=GCR codes |date=March 1985 |publisher=[[Transactor Publishing Incorporated]] |location=Milton, Ontario, Canada |isbn=0-9692086-0-X |page=49 |url=http://www.classiccmp.org/cini/pdf/Commodore/The%20Complete%20Commodore%20Inner%20Space%20Anthology.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323143602/http://www.classiccmp.org/cini/pdf/Commodore/The%20Complete%20Commodore%20Inner%20Space%20Anthology.pdf |archive-date=2017-03-23}} [http://www.zimmers.net/anonftp/pub/cbm/manuals/anthology/p049.jpg<!-- https://web.archive.org/web/20170323115314/http://www.zimmers.net/anonftp/pub/cbm/manuals/anthology/p049.jpg -->] (NB. Commodore GCR codes—but this reference erroneously claims that a 1-bit indicates a lack of a transition.)</ref>
<ref name="Keong_GCR">{{citation |title=Computer Peripherals |at=Chapter 7. Magnetic Recording Fundamentals |author-first=Kwoh Chee |author-last=Keong |publisher=School of Computer Engineering, [[Nanyang Technological University]], Singapore |url=http://www.lintech.org/comp-per/07MAGREC.pdf |access-date=2017-03-23 |url-status=live |archive-url=https://web.archive.org/web/20170323134401/http://www.lintech.org/comp-per/07MAGREC.pdf |archive-date=2017-03-23}}</ref>
<ref name="Guzis_2009_Micropolis">{{cite web |title=Durango GCR |author-first=Charles "Chuck" P. |author-last=Guzis |publisher=Sydex |date=2009-09-13 |url=http://www.vcfed.org/forum/archive/index.php/t-17262.html<!-- http://www.vcfed.org/forum/showthread.php?17262-5-25-quot-floppy-disks-with-bad-sectors-any-solutions/page4 --> |access-date=2017-03-25 |url-status=live |archive-url=https://web.archive.org/web/20171104185445/http://www.vcfed.org/forum/archive/index.php/t-17262.html |archive-date=2017-11-04}}</ref>
<ref name="IWM_1982">{{cite book |title=Integrated Woz Machine (IWM) Specification |edition=19 |publisher=DigiBarn Computer Museum |author=Apple Computer, Inc. |author-link=Apple Computer, Inc. |date=February 1982 |orig-year=1978 |url=http://www.brutaldeluxe.fr/documentation/iwm/apple2_IWM_Spec_Rev19_1982.pdf |access-date=2016-08-06 |url-status=live |archive-url=https://web.archive.org/web/20160806095036/http://www.brutaldeluxe.fr/documentation/iwm/apple2_IWM_Spec_Rev19_1982.pdf |archive-date=2016-08-06}}</ref>
<ref name="Micropolis_1979_DiskMaint">{{cite book |title=Micropolis Maintenance Manual Floppy Disk Subsystem |publisher=[[Micropolis Corporation]] |id=1082-04 |edition=revision 1, 1st |date=February 1979 |url=http://bitsavers.trailing-edge.com/pdf/micropolis/metafloppy/1084-02_Micropolis_Floppy_Disk_Subsystem_Maintenance_Manual_Feb79.pdf |access-date=2017-06-12 |url-status=live |archive-url=https://web.archive.org/web/20170612210907/http://bitsavers.trailing-edge.com/pdf/micropolis/metafloppy/1084-02_Micropolis_Floppy_Disk_Subsystem_Maintenance_Manual_Feb79.pdf |archive-date=2017-06-12}} (NB. Micropolis 100163-51-8 and 100163-52-6 are GCR-based.)</ref>
<ref name="IW_1980_Micropolis">{{cite journal |title=InfoNews/Hardware: Hardware/Briefs |journal=[[InfoWorld]] |volume=2 |number=2 |date=1980-03-03 |page=19 |url=https://books.google.com/books?id=aj4EAAAAMBAJ&pg=PT42 |access-date=2017-06-12 |quote=[...] Four new 96 tracks-per-inch products have been added to [[Micropolis Corporation|Micropolis]]' current line of 100 tpi single-sided and double-sided floppy disks. The 96 tpi drives offer 70 tracks-per-side, as opposed to the 77 offered by the [[MegaFloppy]] line. The four models are: 1) The 1015-V: 436&nbsp;KB, unformatted, FM/MFM recording [...] 2) The 1016-V: 532&nbsp;KB unformatted, [[Group Coded Recording]] (GCR) [...] 3) The 1015-VI: a two-head version of the MFM drive, 872&nbsp;KB [...] 4) The 1016-VI: also a two-head drive, 1.064 MB GCR encoding [...]}}</ref>
<ref name="Moseley_1979_Byte">{{cite journal |title=Technical Forum: A Comparison of Bar Code Encoding Schemes |author-first=Robin C. |author-last=Moseley |location=Andover, MA, USA |journal=[[BYTE]] |date=April 1979 |volume=4 |number=4 |pages=50, 52 |url=http://www.americanradiohistory.com/Archive-Byte/70s/Byte-1979-04.pdf |access-date=2017-06-14}}</ref>
<ref name="Gieseke_2003_Brother">{{cite web |title=Brother WP-1 |author-first=Hans-Werner |author-last=Gieseke |date=2003-08-27 |language=de |url=http://de.alt.folklore.computer.narkive.com/8FzmdtOA/brother-wp-1 |access-date=2017-06-14 |url-status=live |archive-url=https://web.archive.org/web/20170614234300/http://de.alt.folklore.computer.narkive.com/8FzmdtOA/brother-wp-1 |archive-date=2017-06-14}} (NB. Reportedly, the Brother WP-1 technical data was derived from page 109 of the user manual.)</ref>
<ref name="Mick_2002_Brother_WP-6">{{cite web |author-first=Mick |author-last=French |title=Brother WP-6 |date=2002-09-13 |url=http://myweb.tiscali.co.uk/mickfrench/brotherwp6.htm |access-date=2017-06-14 |quote=[...] The 3.5" 240Kb disk drive is a single head Brother part no.13194989 and is connected with a 15 pin ribbon. [...] it initializes (formats) the disk to a capacity of 236.5Kb. [...] |archive-date=2017-11-22  |archive-url=https://web.archive.org/web/20171122120112/http://myweb.tiscali.co.uk/mickfrench/brotherwp6.htm |url-status=dead }}</ref>
<ref name="Cotgrove_2009_Brother">{{cite web |title=archaic floppy disc format |author-first=Michael S. |author-last=Cotgrove |date=2009-02-26 |url=https://groups.google.com/forum/#!msg/comp.sys.ibm.pc.hardware.storage/MajJ_2qJBk0/jZnlyCTZkgYJ |access-date=2017-06-14 |quote=[...] There were several 3.5" Brother disks that are completely nonstandard. [...] One had 1296 byte sectors and another had 12 x 256 byte GCR sectors [...]}}</ref>
<ref name="Sargent_1988">{{cite book |title=Assemblersprache und Hardware des IBM PC/XT/AT |language=de  |author-first1=Murray |author-last1=Sargent III. |author-first2=Richard L. |author-last2=Shoemaker |author-first3=Ernst H. K. |author-last3=Stelzer |publisher=[[Addison-Wesley Verlag (Deutschland) GmbH]] / [[Addison-Wesley Publishing Company]] |edition=1 |date=1988 |isbn=3-89319-110-0 |id=. VVA-Nr. 563-00110-4}}</ref>
<ref name="Geoffroy_2002">{{cite book |title=Design of Dependable Computing Systems |chapter=15.12 Exercise GCR (4B – 5B) code |author-first1=Jean-Claude |author-last1=Geffroy |author-first2=Gilles |author-last2=Motet |author-link2=Gilles Motet <!-- |translator-first=Irene |translator-last=Aleksanova original title: "Linear Programming" by F.P. Vasilyev and A. Yu. Ivanitskiy, published in the Russian language by Factorial, Moscow, 1998 ??? --> |publisher=[[Springer Science+Business Media, B.V.]] / [[Kluwer Academic Publishers]] |location=Toulouse, France |isbn=978-1-4020-0437-7 |lccn=2002-284974 |id={{ISBN|94-015-9884-3}} |date=2013-03-09 |orig-date=2002 |pages=426, 591 |url=https://books.google.com/books?id=9uaoCAAAQBAJ&pg=PA426 |access-date=2021-11-18}} (672 pages)</ref>
}}