Allen, David (February 1978). «A Minifloppy Interface». BYTE (Kansas City, USA) 3 (2): 114, 116-118, 120, 122, 134-125. Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. «[…] 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. […]».[1]
«Supplemental Technical Reference Material». Revision 0 (1st printing edición). Scotts Valley, CA, USA: Victor Publications. 23 de marzo de 1983. Application Note: 002. «[…] Single-sided floppy drive offers 80 tracks at 96 TPI […] Double-sided floppy drive offers 160 tracks at 96 TPI […] Floppy drives have 512 byte sectors; utilising a GCR, 10-bit recording technique. […] Although the Victor 9000 uses 5 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 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.»
CW staff (14 de marzo de 1973). «6,250 Byte/In. Density - IBM 3420 Storage More Than Tripled». Computerworld (White Plains, New York, USA) VII (11): 1-2. Consultado el 23 de marzo de 2017. «IBM added three new models to the 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 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. […]».
«NCC Preview: OEMs at NCC - Micropolis Corp.». Computerworld (CW Communications, Inc.) XII (22): P/50. 28 de mayo de 1978. Consultado el 12 de junio de 2017. «[…] 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 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 comprised 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-chained to a common host for a maximum on-line storage capacity of more than 15M bytes […]».
«InfoNews/Hardware: Hardware/Briefs». InfoWorld2 (2): 19. 3 de marzo de 1980. Consultado el 12 de junio de 2017. «[…] Four new 96 tracks-per-inch products have been added to 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 KB, unformatted, FM/MFM recording […] 2) The 1016-V: 532 KB unformatted, Group Coded Recording (GCR) […] 3) The 1015-VI: a two-head version of the MFM drive, 872 KB […] 4) The 1016-VI: also a two-head drive, 1.064 MB GCR encoding […]».
Hildon, Karl J. H. (March 1985). «GCR codes». The Complete Commodore Inner Space Anthology. Milton, Ontario, Canada: Transactor Publishing Incorporated. p. 49. ISBN0-9692086-0-X. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017.[7] (NB. Commodore GCR codes—but this reference erroneously claims that a 1-bit indicates a lack of a transition.)
US 4261019, McClelland, S. Barry, "Compatible Digital Magnetic Recording System", published 1981-04-07, assigned to Micropolis Corporation (NB. Application Number: US 06/098381)
Cotgrove, Michael S. (26 de febrero de 2009). «archaic floppy disc format». Consultado el 14 de junio de 2017. «[…] 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 […]».
Guzis, Charles "Chuck" P. (20 de septiembre de 2015). «Multi-platform distribution format». Sydex. Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. «[…] 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 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. […]».
mirrorservice.org
«Chapter 7. Disk Drive Assembly». Victor 9000 Technical Reference Manual. Victor Business Products, Inc. June 1982. pp. 7-1..7-9. 710620. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017. «[…] Track density is 96 tracks per inch, and recording density is maintained at approximately 8000 bits per inch on all tracks. […] The 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. […]».
narkive.com
de.alt.folklore.computer.narkive.com
Gieseke, Hans-Werner (27 de agosto de 2003). «Brother WP-1»(en alemán). Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. (NB. Reportedly, the Brother WP-1 technical data was derived from page 109 of the user manual.)
Allen, David (February 1978). «A Minifloppy Interface». BYTE (Kansas City, USA) 3 (2): 114, 116-118, 120, 122, 134-125. Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. «[…] 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. […]».[1]
sharppocketcomputers.com
«Model CE-1600F». Sharp PC-1600 Service Manual. Yamatokoriyama, Japan: Sharp Corporation, Information Systems Group, Quality & Reliability Control Center. July 1986. pp. 98-104. Archivado desde el original el 7 de mayo de 2017. Consultado el 23 de marzo de 2017. «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.»
Guzis, Charles "Chuck" P. (October 2006). «The Durango F-85 Computer». Sydex. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017.
thegalleryofoldiron.com
«The Gallery of Old Iron». 2004. Archivado desde el original el 25 de diciembre de 2008. «[…] I moved to the lab at Poughkeepsie in 1958 […] I later was Lead designer and architect for the 2802 Tape Control Unit and a few years after that, Lead Designer and Architect of the 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. […]». (NB. An anonymous comment by one of the developers on the origin of the name "Group Coded Recording".)
tiscali.co.uk
myweb.tiscali.co.uk
French, Mick (13 de septiembre de 2002). «Brother WP-6». Archivado desde el original el 22 de noviembre de 2017. Consultado el 14 de junio de 2017. «[…] 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. […]».
Guzis, Charles "Chuck" P. (13 de septiembre de 2009). «Durango GCR». Sydex. Archivado desde el original el 4 de noviembre de 2017. Consultado el 25 de marzo de 2017.
web.archive.org
«The Gallery of Old Iron». 2004. Archivado desde el original el 25 de diciembre de 2008. «[…] I moved to the lab at Poughkeepsie in 1958 […] I later was Lead designer and architect for the 2802 Tape Control Unit and a few years after that, Lead Designer and Architect of the 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. […]». (NB. An anonymous comment by one of the developers on the origin of the name "Group Coded Recording".)
Guzis, Charles "Chuck" P. (20 de septiembre de 2015). «Multi-platform distribution format». Sydex. Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. «[…] 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 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. […]».
Allen, David (February 1978). «A Minifloppy Interface». BYTE (Kansas City, USA) 3 (2): 114, 116-118, 120, 122, 134-125. Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. «[…] 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. […]».[1]
Guzis, Charles "Chuck" P. (13 de septiembre de 2009). «Durango GCR». Sydex. Archivado desde el original el 4 de noviembre de 2017. Consultado el 25 de marzo de 2017.
Guzis, Charles "Chuck" P. (October 2006). «The Durango F-85 Computer». Sydex. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017.
Hildon, Karl J. H. (March 1985). «GCR codes». The Complete Commodore Inner Space Anthology. Milton, Ontario, Canada: Transactor Publishing Incorporated. p. 49. ISBN0-9692086-0-X. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017.[7] (NB. Commodore GCR codes—but this reference erroneously claims that a 1-bit indicates a lack of a transition.)
«Chapter 7. Disk Drive Assembly». Victor 9000 Technical Reference Manual. Victor Business Products, Inc. June 1982. pp. 7-1..7-9. 710620. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017. «[…] Track density is 96 tracks per inch, and recording density is maintained at approximately 8000 bits per inch on all tracks. […] The 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. […]».
Gieseke, Hans-Werner (27 de agosto de 2003). «Brother WP-1»(en alemán). Archivado desde el original el 14 de junio de 2017. Consultado el 14 de junio de 2017. (NB. Reportedly, the Brother WP-1 technical data was derived from page 109 of the user manual.)
French, Mick (13 de septiembre de 2002). «Brother WP-6». Archivado desde el original el 22 de noviembre de 2017. Consultado el 14 de junio de 2017. «[…] 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. […]».
«Model CE-1600F». Sharp PC-1600 Service Manual. Yamatokoriyama, Japan: Sharp Corporation, Information Systems Group, Quality & Reliability Control Center. July 1986. pp. 98-104. Archivado desde el original el 7 de mayo de 2017. Consultado el 23 de marzo de 2017. «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.»
Hildon, Karl J. H. (March 1985). «GCR codes». The Complete Commodore Inner Space Anthology. Milton, Ontario, Canada: Transactor Publishing Incorporated. p. 49. ISBN0-9692086-0-X. Archivado desde el original el 23 de marzo de 2017. Consultado el 23 de marzo de 2017.[7] (NB. Commodore GCR codes—but this reference erroneously claims that a 1-bit indicates a lack of a transition.)
![[7]](http://www.zimmers.net/anonftp/pub/cbm/manuals/anthology/p049.jpg){kind=link}