The Commodore 1581 is a 3½-inch
double-sided double-density
Disk density is a capacity designation on magnetic storage, usually floppy disks. Each designation describes a set of characteristics that can affect the areal density of a disk or the efficiency of the encoded data. Such characteristics include ...
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent 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 w ...
drive that was released by
Commodore Business Machines (CBM) in 1987, primarily for its
C64
The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness Wo ...
and
C128 home
A home, or domicile, is a space used as a permanent or semi-permanent residence for one or many humans, and sometimes various companion animals. It is a fully or semi sheltered space and can have both interior and exterior aspects to it. H ...
/
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
s. The drive stores 800
kilobyte
The kilobyte is a multiple of the unit byte for digital information.
The International System of Units (SI) defines the prefix ''kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quantiti ...
s using an
MFM encoding
but formats different from the
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
(720 kB),
Amiga
Amiga is a family of personal computers introduced by Commodore in 1985. The original model is one of a number of mid-1980s computers with 16- or 32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphi ...
(880 kB), and
Mac Plus (800 kB) formats. With special software it's possible to read C1581 disks on an x86 PC system, and likewise, read MS-DOS and other formats of disks in the C1581 (using Big Blue Reader), provided that the PC or other floppy handles the size format.
[ This capability was most frequently used to read MS-DOS disks. The drive was released in the summer of 1987 and quickly became popular with bulletin board system (BBS) operators and other users.
Like the ]1541
__NOTOC__
Year 1541 ( MDXLI) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar.
Events
January–June
* February 12 – Pedro de Valdivia founds Santiago del Nuevo Extremo, whi ...
and 1571
Year 1571 ( MDLXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar.
Events
January–June
* January 11 – The Austrian nobility are granted freedom of religion.
* January 23 &nd ...
, the 1581 has an onboard MOS Technology 6502 CPU with its own ROM and RAM, and uses a serial version of the IEEE-488 interface. Inexplicably, the drive's ROM contains commands for parallel use, although no parallel interface was available. Unlike the 1571, which is nearly 100% backward-compatible with the 1541, the 1581 is only compatible with previous Commodore drives at the DOS level and cannot utilize software that performs low-level disk access (as the vast majority of Commodore 64 games do).
The version of Commodore DOS
Commodore DOS, also known as CBM DOS, is the disk operating system used with Commodore's 8-bit computers. Unlike most other DOSes, which are loaded from disk into the computer's own RAM and executed there, CBM DOS is executed internally in the dr ...
built into the 1581 added support for partitions
Partition may refer to:
Computing Hardware
* Disk partitioning, the division of a hard disk drive
* Memory partition, a subdivision of a computer's memory, usually for use by a single job
Software
* Partition (database), the division of a ...
, which could also function as fixed-allocation subdirectories. PC-style subdirectories were rejected as being too difficult to work with in terms of block availability maps, then still much in vogue, and which for some time had been the traditional way of inquiring into block availability. The 1581 supports the C128's burst mode for fast disk access, but not when connected to an older Commodore machine like the Commodore 64
The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness ...
. The 1581 provides a total of 3160 blocks free when formatted (a block being equal to 256 byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
s). The number of permitted directory entries was also increased, to 296 entries. With a storage capacity of 800 kB, the 1581 is the highest-capacity serial-bus drive that was ever made by Commodore (the 1-MB SFD-1001 uses the parallel IEEE-488), and the only 3½" one. However, starting in 1991, Creative Micro Designs (CMD) made the FD-2000
The HQ-9 () is a long-range semi-active radar homing (SARH) surface-to-air missile (SAM) developed by the People's Republic of China. The naval variant is the HHQ-9 ().
Description
The HQ-9 is a derivative of the Russian S-300 missile system, ...
high density (1.6 MB) and FD-4000 extra-high density
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent 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 wi ...
(3.2 MB) 3½" drives, both of which offered not only a 1581-emulation mode but also 1541- and 1571-compatibility modes.
Like the 1541
__NOTOC__
Year 1541 ( MDXLI) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar.
Events
January–June
* February 12 – Pedro de Valdivia founds Santiago del Nuevo Extremo, whi ...
and 1571
Year 1571 ( MDLXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar.
Events
January–June
* January 11 – The Austrian nobility are granted freedom of religion.
* January 23 &nd ...
, a nearly identical job queue
In system software, a job queue ( batch queue, input queue), is a data structure maintained by job scheduler software containing jobs to run.
Users submit their programs that they want executed, "jobs", to the queue for batch processing.
The s ...
is available to the user in zero page (except for job 0), providing for exceptional degrees of compatibility.
Unlike the cases of the 1541 and 1571, the low-level disk format used by the 1581 is similar enough to the MS-DOS format as the 1581 is built around a WD1770
The FD1771, sometimes WD1771, is the first in a line of floppy disk controllers produced by Western Digital. It uses single density FM encoding introduced in the IBM 3740. It is packaged in a 40-pin DIP."The FD1771 is a single-chip floppy disk f ...
FM/MFM floppy controller chip. The 1581 disk format consists of 80 tracks and ten 512 byte sectors per track, used as 20 logical sectors of 256 bytes each. Special software is required to read 1581 disks on a PC due to the different file system. An internal floppy drive and controller are required as well; USB floppy drives operate strictly at the file system level and do not allow low-level disk access. The WD1770 controller chip, however, was the seat of some early problems with 1581 drives when the first production runs were recalled due to a high failure rate; the problem was quickly corrected. Later versions of the 1581 drive have a smaller, more streamlined-looking external power supply provided with them.
Specifications
1581 Image Layout
The 1581 disk has 80 logical tracks, each with 40 logical sectors (the actual physical layout of the diskette is abstracted and managed by a hardware translation layer). The directory starts on 40/3 (track 40, sector 3). The disk header is on 40/0, and the BAM (block availability map) resides on 40/1 and 40/2.
Header Contents
$00–01 T/S reference to first directory sector (40/3)
02 DOS version ('D')
04-13 Disk Label, $A0 padded
16-17 Disk ID
19-1A DOS type ('3D')
BAM Contents, 40/1
$00–01 T/S to next BAM sector (40/2)
02 DOS version ('D')
04-05 Disk ID
06 I/O byte
07 Autoboot flag
10-FF BAM entries for Tracks 1-40
BAM Contents, 40/2
$00–01 00/FF
02 DOS version ('D')
04-05 Disk ID
06 I/O byte
07 Autoboot flag
10-FF BAM entries for Tracks 41-80
See also
* Commodore 64 peripherals
* Commodore 128
The Commodore 128, also known as the C128, C-128, C= 128,The "C=" represents the graphical part of the logo. is the last 8-bit home computer that was commercially released by Commodore Business Machines (CBM). Introduced in January 1985 at the ...
References
External links
d81.de: Permanent home of 1581-Copy
A MS-Windows based Tool uses any standard x86-PC 3.5" drive to WRITE & READ 1581 disk images (d81).
Tools & Games specifically for the 1581 disk drive.
How to use a PC 3.5" floppy drive in the 1581 device
vice-emu: Commodore compatible Disk Drives
drive info
C1581 clone (complete)
{{Commodore disk drives
Products introduced in 1987
Commodore 64
CBM floppy disk drives