The CMD FD series was Creative Micro Designs

Creative Micro Designs

Creative Micro Designs is a computer technologies company which today sells PCs and related equipment, but which started out in 1987 selling self-designed firmware updates and hardware for the Commodore 64 and C128 8-bit home/personal computers....

 (CMD)'s range of third-party floppy disk

Floppy disk

A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

 drives for the Commodore

Commodore International

Commodore is the commonly used name for Commodore Business Machines , the U.S.-based home computer manufacturer and electronics manufacturer headquartered in West Chester, Pennsylvania, which also housed Commodore's corporate parent company, Commodore International Limited...

 8-bit

8-bit

The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...

 line of home computer

Home computer

Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...

s. Using 3½" floppy disks, they provided a significantly larger storage capacity than Commodore-produced drives; the FD-2000 offered 1600KB

Kilobyte

The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...

 of storage using standard double-sided, high-density floppies, while the FD-4000 also allowed the use of 3200KB extended-density floppies. In contrast, the Commodore 1581

Commodore 1581

The Commodore 1581 is a 3½ inch double sided double density floppy disk drive made by Commodore Business Machines primarily for its C64 and C128 home/personal computers. The drive stores 800 kilobytes using an MFM encoding but format different from both MS-DOS , and the Amiga formats. With...

 3½" drive only supported 800KB double-sided, double-density disks.

Features

In addition to the higher storage capacity, the FD series also provided additional features not found on the Commodore 1581. A "SWAP" button on the front panel allowed the drive number to be easily switched with that of another Commodore drive on the serial bus, without the need to enter any commands into the computer. It also provided a "1541 emulation mode", allowing partitions on a 3½" disk to simulate the behavior of a 5¼" Commodore 1541

Commodore 1541

The Commodore 1541 , made by Commodore International, was the best-known floppy disk drive for the Commodore 64 home computer. The 1541 was a single-sided 170 kilobyte drive for 5¼" disks...

 floppy. The ability to use partitions and subdirectories was also expanded beyond the rudimentary form found in the 1581. A real-time clock was also available as an add-on feature; it could be used to time-stamp files and to automatically set the system clock in the GEOS

GEOS (8-bit operating system)

GEOS is an operating system from Berkeley Softworks . Originally designed for the Commodore 64 and released in 1986, it provided a graphical user interface for this popular 8-bit computer.GEOS closely resembled early versions of Mac OS and included a graphical word processor and paint program...

 operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

. The CMD FD series also included native JiffyDOS compatibility; while using the JiffyDOS system with a Commodore drive required replacing both the KERNAL

KERNAL

The KERNAL is Commodore's name for the ROM-resident operating system core in its 8-bit home computers; from the original PET of 1977, followed by the extended but strongly related versions used in its successors; the VIC-20, Commodore 64, Plus/4, C16, and C128...

 and drive ROM

Read-only memory

Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

chips, for full JiffyDOS use, only the computer's KERNAL ROM needed to be replaced when used in conjunction with an FD-2000 or FD-4000.

Native Partition Structure

The System Partition header is at track 26, sectors 5, 8, 9, 10, and 11. Sector 5 is the Device Information Block, which is $FF filled except in a few specific places. Sectors 8 thru 11 contain the System Partition Directory.

The first sector of a FD2000 native partition is the header.

Header Contents
$00-01: T/S reference to root directory block of this
partition ($01/$24).
02: DOS Type ("H")
04-15: Disk label, $A0 padded
16-17: Disk ID
19-1A: DOS Version ("1H")
20-21: T/S reference to present directory header block
22-23: T/S reference to parent directory header block
(set to $00/$00 when at the top of the directory)
24-25: T/S reference to dir entry in previous directory
(set to $00/$00 when at the top of the directory)
26: Index to parent directory entry ($00 at the top)
AB-AC: GEOS border sector
AD-BC: GEOS format string (GEOS format Vx.x)

The BAM (Block Allocation Map) starts at 1/2 (track 1, sector 2) and continues to 1/33.

BAM Contents
02: DOS Type ("H")
04-05: Disk ID
06: I/O byte (as the 1581)
bit 7 set - Verify on
bit 7 clear - Verify off
bit 6 set - Check header CRC
bit 6 clear - Don't check header CRC
08: Last available track # in partition ($19=#25)
20-FF: BAM for tracks 1-7

Its directory structure is slightly different from the Commodore structure.