A report on Group coded recording and Zone bit recording

Physical layout of sectors in a zone-bit disc: As distance from the centre increases, the number of sectors in a given angle increases from one (red) to two (green) to four (grey).

Commodore 1541 floppy disk (combined ZBR, ZCAV and GCR for 17–21 sectors á 256 bytes in 4 writing speed zones)

- Zone bit recording

This more efficient GCR scheme, combined with an approach at constant bit-density recording by gradually increasing the clock rate (zone constant angular velocity, ZCAV) and storing more physical sectors on the outer tracks than on the inner ones (zone bit recording, ZBR), enabled Commodore to fit 170 kB on a standard single-sided single-density 5.25-inch floppy, where Apple fit 140 kB (with 6-and-2 encoding) or 114 kB (with 5-and-3 encoding) and an FM-encoded floppy held only 88 kB.

- Group coded recording
Physical layout of sectors in a zone-bit disc: As distance from the centre increases, the number of sectors in a given angle increases from one (red) to two (green) to four (grey).

2 related topics with Alpha

Overall
8-inch, 5¼-inch, and 3½-inch floppy disks

Floppy disk

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Obsolete type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a fabric that removes dust particles from the spinning disk.

Obsolete type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a fabric that removes dust particles from the spinning disk.

8-inch, 5¼-inch, and 3½-inch floppy disks
8-inch, 5¼-inch (full height), and 3½-inch drives
A 3½-inch floppy disk removed from its housing
8-inch floppy disk, inserted in drive, (3½-inch floppy diskette, in front, shown for scale)
3½-inch, high-density floppy diskettes with adhesive labels affixed
Imation USB floppy drive, model 01946: an external drive that accepts high-density disks
Front and rear of a retail 3½-inch and 5¼-inch floppy disk cleaning kit, as sold in Australia at retailer Big W, circa early 1990s
Different data storage media (Examples include: Flash drive, CD, Tape drive, and CompactFlash)
A floppy hardware emulator, same size as a 3½-inch drive, provides a USB interface to the user
Screenshot depicting a floppy disk as "save" icon
Inside the 8-inch floppy disk
Disk notcher converts single-sided 5¼-inch diskettes to double-sided.
Rear side of a 3½-inch floppy disk in a transparent case, showing its internal parts
The spindle motor from a 3½‑inch unit
A read-write head from a 3½‑inch unit
How the read-write head is applied on the floppy
Visualization of magnetic information on floppy disk (image recorded with CMOS-MagView)
8-inch floppy disk
A 3 1⁄2-inch floppy disk drive
A box of about 80 floppy disks together with one USB memory stick. The stick is capable of holding over 130 times as much data as the entire box of disks put together.

There were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as differential Manchester encoding (DM), modified frequency modulation (MFM), M2FM and group coded recording (GCR).

A more space-efficient technique would be to increase the number of sectors per track toward the outer edge of the disk, from 18 to 30 for instance, thereby keeping nearly constant the amount of physical disk space used for storing each sector; an example is zone bit recording.

Sirius Systems Technology

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Personal computer manufacturer in Scotts Valley, California.

Personal computer manufacturer in Scotts Valley, California.

One striking difference between it and other machines on the market at the time was the fact that the disc utilized a form of zoned constant linear velocity (ZCLV) (using 9 different speed-zones selected out of 15 supported by the hardware) with a variant of zone bit recording (ZBR) (11 to 19 sectors depending on zone) to spun at different speeds according to where the data was stored, running slower towards the outer edge of the disc in such a way that bit density (bits per cm passing the head), rather than rotational speed, was approximately constant.

This, combined with group-coded recording (GCR), allowed standard floppy disks to hold more data than others at the time, 600 KB on single- and 1.2 MB on double-sided floppies compared with 140–160 KB per side of other machines such as the Apple II and early IBM PC, but disks made at constant bit density were not compatible with machines with standard drives.