Commodore 1581
Encyclopedia
Double-sided disk
In computer science, a double-sided disk is a disk of which both sides are used to store data.Early floppy disks only used one surface for recording. The term "single sided disk" was not common until the introduction of double-sided disks, which offered double the capacity in the same physical size...
double density
Double density
Double density, often shortened DD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding of information, which can encode on average twice as many bits per time unit compared to single density...
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...
drive made by Commodore Business Machines (CBM)
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...
primarily for its C64
Commodore 64
The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
and C128
Commodore 128
The Commodore 128 home/personal computer was the last 8-bit machine commercially released by Commodore Business Machines...
home
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...
/personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s. The drive stores 800 kilobyte
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...
s using an MFM
Modified Frequency Modulation
Modified Frequency Modulation, commonly MFM, is a line coding scheme used to encode the actual data-bits on most floppy disk formats, hardware examples include Amiga, most CP/M machines as well as IBM PC compatibles. Early hard disk drives also used this coding.MFM is a modification to the original...
encoding but format different from both MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
(720 kB), and the Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
(880 kB) formats. With special software it's possible to read C1581 disks on a x86 PC system. And read MS-DOS disks in the C1581 (Big blue reader) provided the PC floppy handles the "720 kB" size format. It was released in the summer of 1987 and quickly became popular with bulletin board system (BBS)
Bulletin board system
A Bulletin Board System, or BBS, is a computer system running software that allows users to connect and log in to the system using a terminal program. Once logged in, a user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging...
operators and other users.
Like the 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...
and 1571
Commodore 1571
The Commodore 1571 was Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it had the ability to utilize double-sided, double-density floppy disks natively. This was in contrast to its predecessors, the 1541 and 1570, which could fully utilize such disks only if the...
, the 1581 has an on board MOS Technology 6502
MOS Technology 6502
The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...
CPU with its own ROM and RAM, and uses a serial version of the IEEE-488
IEEE-488
IEEE-488 is a short-range digital communications bus specification. It was created for use with automated test equipment in the late 1960s, and is still in use for that purpose. IEEE-488 was created as HP-IB , and is commonly called GPIB...
interface. Inexplicably, the drive's ROM contains commands for parallel use, although no parallel interface was available. Like the 1571, it can read various other disk formats using special software. This capability was most frequently used to read MS-DOS disks. However, unlike the 1571, which is nearly 100% backward-compatible with the 1541, the 1581 has limited compatibility with Commodore's earlier drives. Although it responds to the same DOS commands, most disk utilities written prior to 1987, most notably fast loaders, are so 1541-specific that they do not work with the 1581.
The version of Commodore DOS
Commodore DOS
Commodore DOS, aka CBM DOS, was the disk operating system used with Commodore's 8-bit computers. Unlike most other DOS systems before or since—which are booted from disk into the main computer's own RAM at startup, and executed there—CBM DOS was executed internally in the drive: the DOS...
built into the 1581 added support for partitions
Disk partitioning
Disk partitioning is the act of dividing a hard disk drive into multiple logical storage units referred to as partitions, to treat one physical disk drive as if it were multiple disks. Partitions are also termed "slices" for operating systems based on BSD, Solaris or GNU Hurd...
, which could also function as fixed-allocation subdirectories
Directory (file systems)
In computing, a folder, directory, catalog, or drawer, is a virtual container originally derived from an earlier Object-oriented programming concept by the same name within a digital file system, in which groups of computer files and other folders can be kept and organized.A typical file system may...
. PC style subdirectories were rejected as being too difficult to work with in terms of Block Allocation Maps, then still much in vogue, and which for some time had been the traditional way of inquiring into block availability. When used together with the C128, it implements faster burst mode
Burst mode (computing)
Burst mode is a generic computing term referring to any situation in which a device is transmitting data repeatedly without waiting for input from another device or waiting for an internal process to terminate before continuing the transfer of data.In the case of DMA, the DMA controller and the...
access than the Commodore 1571
Commodore 1571
The Commodore 1571 was Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it had the ability to utilize double-sided, double-density floppy disks natively. This was in contrast to its predecessors, the 1541 and 1570, which could fully utilize such disks only if the...
5¼" drive. When using the 1581 together with the older C64, however, it is almost as slow as the older 1541 drive, due to limitations of the C64's ROM code. The 1581 provides a total of 3160 blocks free when formatted (a block being equal to 256 byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s). The number of permitted directory entries was also increased, to 288 entries. With a storage capacity of 800 KB, the 1581 was the highest capacity serial bus drive ever made by Commodore (the 1 MB SFD-1001 used the parallel IEEE-488), and the only 3½" one. However, starting in 1991, Creative Micro Designs (CMD)
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....
made the FD-2000 high density (1.6 MB) and FD-4000 extended density (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
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...
and 1571
Commodore 1571
The Commodore 1571 was Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it had the ability to utilize double-sided, double-density floppy disks natively. This was in contrast to its predecessors, the 1541 and 1570, which could fully utilize such disks only if the...
, a nearly identical job queue is available to the User in Zero page
Zero page
The zero page is the series of memory addresses at the absolute beginning of a computer's address space; that is, the page whose starting address is zero. The size of a "page" depends on the context, and the significance of zero-page memory versus higher addressed memory is highly dependent on...
(except for Job 0), providing for exceptional degrees of compatibility.
Unlike the case 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 FM/MFM floppy controller chip. PC Floppy controllers (ISA or onboard, but not USB floppy drives) are able to deal with the 1581 format without need for any special tricks. Thus, utilities to format, read, and write 1581-format disks in standard PC floppy drives under Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
or Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
exist. This 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 had a smaller, more streamlined looking external power supply provided with them.
Specifications
- Onboard CPU: MOS Technology 6502MOS Technology 6502The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...
@ 2 MHz - RAM: 8 kBKilobyteThe 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...
- ROM: 32 kB
- Transfer protocols: Standard and fast serial; burst modeBurst mode (computing)Burst mode is a generic computing term referring to any situation in which a device is transmitting data repeatedly without waiting for input from another device or waiting for an internal process to terminate before continuing the transfer of data.In the case of DMA, the DMA controller and the...
; and commands for parallel interface (the latter not used) - Disk type: 3,5" inch
- Storage format: MFMModified Frequency ModulationModified Frequency Modulation, commonly MFM, is a line coding scheme used to encode the actual data-bits on most floppy disk formats, hardware examples include Amiga, most CP/M machines as well as IBM PC compatibles. Early hard disk drives also used this coding.MFM is a modification to the original...
, double density, double-sided - Interface: CBM's proprietary serial IEEE-488
- Power: @ , @
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 Allocation 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
External links
- viceteam.org - drive info
- tut.fi - C1581 clone (complete)