The Commodore serial IEEE-488 bus, is Commodore's interface for magnetic disk data storage and printers for the Commodore 8-bit home/personal computers, notably the VIC-20, C64, C128, Plus/4, C16 and C65. The parallel IEEE-488 interface used on the Commodore PET computer line was too costly, so a cost reduced version was developed, which consisted of a stripped down, serial version of the IEEE-488 interface, with only a few signals remaining. Commodore began using this bus with the VIC-20. Connection to the computer utilizes a DIN-6 connector; the bus signals are active when negative. Bus devices have to provide their own power; because the bus lines are electrically open collector it works like a long OR gate between all device line drivers. The logical value for ground is true and vice versa. Any device may set a line "true". A line only becomes "false". Transmission begins with the bus talker holding the Clock line true, the listener holding the Data line true. To begin the talker releases the Clock line to false.
When all bus listeners are ready to receive they release the Data line to false. If the talker waits more than 200 µs without the Clock line going true, listeners have to perform End-or-Identify. If the Data line being false isn't acknowledged by the talker within 200 µs, the listener knows that the talker is in the process of EOI that means "this character will be the last one." When the listener detects the 200 µs timeout, it must acknowledge this by pulling the Data line true for at least 60 µs, release it. The talker can revert to transmitting again within 60 µs by pulling the Clock line true. Data is eight bits starting with the least significant bit; the Data line is set according to the bit to send. Once the Data line is set, the Clock line is released to false; the Clock and Data lines will be held steady for at least 20 µs. After 8 bits has been sent, the talker releases the Data line to false and the listener acknowledge the talker by pulling the Data line true within 1000 µs. After this the talker sets the Clock line true and listener sets the Data line true thus back where the transmission begun.
If an EOI is signaled by holding the Clock line false the transmission is ended and the listener acknowledge this by pulling the Data line true for 200 µs. The ATN line is set to true and bytes are sent like above to all devices, but the byte is interpreted as one of the commands "Talk," "Listen," "Untalk," and "Unlisten"; that tell a specific device to become a listener. Only devices with matching device numbers listen mode. A secondary address may follow. On higher logical level the host will set the ATN line to true and transmit the bytes "Device number 8, listen", "Secondary address 2, open". Next it will set the ATN line false and the host becomes the talker, holding the Clock line true; the device will be the listener. The host will end it with an EOI signal sequence. After this the host will set with ATN line true, "Device number 8, unlisten". Followed up by ATN line true and "Device number 8, listen", "Secondary address 2, data"; the host sets the ATN line false and sends the data. When the host has finished sending data the ATN line is set to true and "Device number 8, unlisten" is sent.
When it is necessary to switch roles and make the host a listener and the device a talker the occurs after a talk command has been sent to the device. The host releases the Clock line to false; the device waits for the Clock line to go false and pulls it to true and release the Data line to false. After this sequence the standard talk-listener interaction may follow. To read a normal file from the floppy device number 8 the command LOAD "filename",8,1 is issued on a Commodore 64; that causes the following high level communication to take place: The Commodore 1541 floppy drive uses a slower Commodore 64 compatible mode which can be deactivated for faster speed by using the command OPEN 15,8,15,"UI-":CLOSE 15. Device number 0–3 will not be sent to the physical bus; the Commodore VIC-20 computer and the Commodore 1540 and 1541 floppy drives use the MOS Technology 6522 VIA to handle IEC Bus transmissions. The Commodore 64 and 128 computers and the Commodore 1571 drive use the Complex Interface Adapter.
The Commodore 1541 floppy drive is the most common peripheral used with this bus and can store 170 KB. Commodore DOS Commodore 64 peripherals List of device bit rates Commodore 1541 Fast loader Magnetic tape data storage IEEE-488, the original parallel version "Saving with 64HDD / XE1541 cable length..." lemon64.com. "Design case history: the Commodore 64". IEEE Spectrum. March 1985. "Serial Bus signal description". Uwaterloo.ca. "IEC disected". Zimmers.net. 2008-02-24. Archived from the original on 2017-01-16. – IEC-bus documentation as used for the 1541-III IEC dissected
The Commodore 128 known as the C128, C-128, C= 128, or CBM 128, is the last 8-bit home computer, commercially released by Commodore Business Machines. Introduced in January 1985 at the CES in Las Vegas, it appeared three years after its predecessor, the bestselling Commodore 64; the C128 is a expanded successor to the C64, with nearly full compatibility. The newer machine has 128 KB of RAM in two 64 KB banks, an 80-column color video output, it has keyboard. Included is a Zilog Z80 CPU which allows the C128 to run CP/M, as an alternative to the usual Commodore BASIC environment; the presence of the Z80 and the huge CP/M software library it brings, coupled with the C64's software library, gives the C128 one of the broadest ranges of available software among its competitors. The primary hardware designer of the C128 was Bil Herd, who had worked on the Plus/4. Other hardware engineers were Dave Haynie and Frank Palaia, while the IC design work was done by Dave DiOrio; the main Commodore system software was developed by Fred Bowen and Terry Ryan, while the CP/M subsystem was developed by Von Ertwine.
The C128's keyboard includes four cursor keys, an Alt key, Help key, Esc key, Tab key and a numeric keypad. None of these were present on the C64 which had only two cursor keys, requiring the use of the Shift key to move the cursor up or left; this alternate arrangement was retained for use under C64 mode. The lack of a numeric keypad, Alt key, Esc key on the C64 was an issue with some CP/M productivity software when used with the C64's Z80 cartridge. A keypad was requested by many C64 owners who spent long hours entering machine language type-in programs. Many of the added keys matched counterparts present on the IBM PC's keyboard and made the new computer more attractive to business software developers. While the 128's 40-column mode duplicates that of the C64, an extra 1K of color RAM is made available to the programmer, as it is multiplexed through memory address 1; the C128's power supply is improved over the C64's unreliable design, being much larger and equipped with cooling vents and a replaceable fuse.
The C128 does not perform a system RAM test on power-up like previous Commodore machines. Instead of the single 6510 microprocessor of the C64, the C128 incorporates a two-CPU design; the primary CPU, the 8502, is a improved version of the 6510, capable of being clocked at 2 MHz. The second CPU is a Zilog Z80, used to run CP/M software, as well as to initiate operating-mode selection at boot time; the two processors cannot run concurrently, thus the C128 is not a multiprocessing system. The C128's complex architecture includes four differently accessed kinds of RAM, two or three CPUs, two different video chips for its various operational modes. Early versions of the C128 experience temperature-related reliability issues due to the use of an electromagnetic shield over the main circuit board; the shield was equipped with fingers that contacted the tops of the major chips, ostensibly causing the shield to act as a large heat sink. A combination of poor contact between the shield and the chips, the inherently limited heat conductivity of plastic chip packages, as well as the poor thermal conductivity of the shield itself, resulted in overheating and failure in some cases.
The SID sound chip is vulnerable in this respect. The most common remedy is to remove the shield, which Commodore had added late in development in order to comply with FCC radio-frequency regulations; the C128 has three operating modes. C128 Mode has both 40 - and 80-column text modes available. CP/M Mode is able to function in both 40 - or 80-column text mode. C64 Mode is nearly 100 percent compatible with the earlier computer. Selection of these modes is implemented via the Z80 chip; the Z80 controls the bus on initial boot-up and checks to see if there is a CP/M disk in the drive, if there are any C64/C128 cartridges present, or if the Commodore key is being depressed on boot-up. Based on these conditions, it will switch to the appropriate mode of operation. In 1984, a year before the release of the Commodore 128, Commodore released the Plus/4. Although targeted at a low-end business market that could not afford the high cost and training requirements of early IBM PC compatibles, it was perceived by the Commodore press as a follow-up to the 64 and would be expected to improve upon that model's capabilities.
While the C64's graphics and sound capabilities were considered excellent, the response to the Plus/4 was one of disappointment. Upon the Plus/4's introduction, repeated recommendations were made in the Commodore press for a new computer called the "C-128" with increased RAM capacity, an 80-column display as was standard in business computers, a new BASIC programming language that made it easy for programmers to use the computer's graphics and sound without resorting to PEEK and POKEs, a new disk drive that improved upon the 1541's abysmal transfer rate, as well as total C64 compatibility; the designers of the C128 succeeded in addressing most of these concerns. A new chip, the VDC, provides the C128 with an 80-column color CGA-compatible display; the then-new 8502 microprocessor is backward-compatible with the C64's 6510, but can run at double the speed if desired. The C64's BASIC 2.0 was replaced with BASIC 7.0, which inc
Data storage is the recording of information in a storage medium. DNA and RNA, phonographic recording, magnetic tape, optical discs are all examples of storage media. Recording is accomplished by any form of energy. Electronic data storage requires electrical power to retrieve data. Data storage in a digital, machine-readable medium is sometimes called digital data. Computer data storage is one of the core functions of a general purpose computer. Electronic documents can be stored in much less space than paper documents. Barcodes and magnetic ink character recognition are two ways of recording machine-readable data on paper. A recording medium is a physical material. Newly created information is distributed and can be stored in four storage media–print, film and optical–and seen or heard in four information flows–telephone, radio and TV, the Internet as well as being observed directly. Digital information is stored on electronic media in many different recording formats. With electronic media, the data and the recording media are sometimes referred to as "software" despite the more common use of the word to describe computer software.
With static media, art materials such as crayons may be considered both equipment and medium as the wax, charcoal or chalk material from the equipment becomes part of the surface of the medium. Some recording media may be temporary either by nature. Volatile organic compounds may be used to preserve the environment or to purposely make data expire over time. Data such as smoke signals or skywriting are temporary by nature. Depending on the volatility, a gas or a liquid surface such as a lake would be considered a temporary recording medium if at all. A 2003 UC Berkeley report estimated that about five exabytes of new information were produced in 2002, that 92% of this data was stored on hard disk drives; this was about twice the data produced in 2000. The amount of data transmitted over telecommunication systems in 2002 was nearly 18 exabytes—three and a half times more than was recorded on non-volatile storage. Telephone calls constituted 98% of the telecommunicated information in 2002; the researchers' highest estimate for the growth rate of newly stored information was more than 30% per year.
It has been estimated that the year 2002 was the beginning of the digital age for information storage: an age in which more information is stored on digital storage devices than on analog storage devices. In 1986 1% of the world's capacity to store information was in digital format; these figures correspond to less than three compressed exabytes in 1986, 295 compressed exabytes in 2007. The quantity of digital storage doubled every three years. In a more limited study, the International Data Corporation estimated that the total amount of digital data in 2007 was 281 exabytes, that the total amount of digital data produced exceeded the global storage capacity for the first time. A study published in 2011 estimated that the world's technological capacity to store information in analog and digital devices grew from less than three exabytes in 1986, to 295 exabytes in 2007, doubles every three years. Data storage portal Bennett, John C.. "'JISC/NPO Studies on the Preservation of Electronic Materials: A Framework of Data Types and Formats, Issues Affecting the Long Term Preservation of Digital Material".
British Library Research and Innovation Report 50. History of Computer Storage from 1928 to 2013 History of Computer Data Storage History of Storage from Cave Paintings to Electrons The Evolution of Data Storage
Commodore International was an American home computer and electronics manufacturer founded by Jack Tramiel. Commodore International, along with its subsidiary Commodore Business Machines, participated in the development of the home–personal computer industry in the 1970s and 1980s; the company developed and marketed the world's best-selling desktop computer, the Commodore 64, released its Amiga computer line in July 1985. With quarterly sales ending 1983 of $49 million, Commodore was one of the world's largest personal computer manufacturers; the company that would become Commodore Business Machines, Inc. was founded in 1954 in Toronto as the Commodore Portable Typewriter Company by Polish-Jewish immigrant and Auschwitz survivor Jack Tramiel. For a few years he had been living in New York, driving a taxicab, running a small business repairing typewriters, when he managed to sign a deal with a Czechoslovakian company to manufacture their designs in Canada, he moved to Toronto to start production.
By the late 1950s a wave of Japanese machines forced most North American typewriter companies to cease business, but Tramiel instead turned to adding machines. In 1955, the company was formally incorporated as Inc. in Canada. In 1962 Commodore went public on the New York Stock Exchange, under the name of Commodore International Limited. In the late 1960s, history repeated itself when Japanese firms started producing and exporting adding machines; the company's main investor and chairman, Irving Gould, suggested that Tramiel travel to Japan to understand how to compete. Instead, Tramiel returned with the new idea to produce electronic calculators, which were just coming on the market. Commodore soon had a profitable calculator line and was one of the more popular brands in the early 1970s, producing both consumer as well as scientific/programmable calculators. However, in 1975, Texas Instruments, the main supplier of calculator parts, entered the market directly and put out a line of machines priced at less than Commodore's cost for the parts.
Commodore obtained an infusion of cash from Gould, which Tramiel used beginning in 1976 to purchase several second-source chip suppliers, including MOS Technology, Inc. in order to assure his supply. He agreed to buy MOS, having troubles of its own, only on the condition that its chip designer Chuck Peddle join Commodore directly as head of engineering. Through the 1970s Commodore produced numerous peripherals and consumer electronic products such as the Chessmate, a chess computer based around a MOS 6504 chip, released in 1978. In December 2007, when Tramiel was visiting the Computer History Museum in Mountain View, for the 25th anniversary of the Commodore 64, he was asked why he called his company Commodore, he said: "I wanted to call my company General, but there's so many Generals in the U. S.: General Electric, General Motors. I went to Admiral, but, taken. So I wind up in Berlin, with my wife, we were in a cab, the cab made a short stop, in front of us was an Opel Commodore." Tramiel gave this account in many interviews, but Opel's Commodore didn't debut until 1967, years after the company had been named.
Once Chuck Peddle had taken over engineering at Commodore, he convinced Jack Tramiel that calculators were a dead end, that they should turn their attention to home computers. Peddle packaged his single-board computer design in a metal case with a keyboard using calculator keys with a full-travel QWERTY keyboard, monochrome monitor, tape recorder for program and data storage, to produce the Commodore PET. From PET's 1977 debut, Commodore would be a computer company. Commodore had been reorganized the year before into Commodore International, Ltd. moving its financial headquarters to the Bahamas and its operational headquarters to West Chester, near the MOS Technology site. The operational headquarters, where research and development of new products occurred, retained the name Commodore Business Machines, Inc. In 1980 Commodore launched production for the European market in Braunschweig. By 1980, Commodore was one of the three largest microcomputer companies, the largest in the Common Market.
The company had lost its early domestic-market sales leadership, however. BYTE stated of the business computer market that "the lack of a marketing strategy by Commodore, as well as its past nonchalant attitude toward the encouragement and development of good software, has hurt its credibility in comparison to the other systems on the market"; the author of Programming the PET/CBM stated in its introduction that "CBM's product manuals are recognized to be unhelpful. Commodore reemphasized the US market with the VIC-20; the PET computer line was used in schools, where its tough all-metal construction and ability to share printers and disk drives on a simple local area network were advantages, but PETs did not compete well in the home setting where graphics and sound were important. This was addressed with the VIC-20 in 1981, introduced at a cost of US$299 and sold in retail stores. Commodore bought aggressive advertisements featuring William Shatner asking consumers "Why buy just a video game?"
The strategy worked and the VIC-20 became the first computer to ship more than one million units. A total of 2.5 million units were sold over the machine's lifetime and helped Commodore's sales to Canadian schools. In another promotion aimed at schools (and as a
Read-only memory is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM can only be modified with difficulty, or not at all, so it is used to store firmware or application software in plug-in cartridges. Read-only memory refers to memory, hard-wired, such as diode matrix and the mask ROM, which cannot be changed after manufacture. Although discrete circuits can be altered in principle, integrated circuits cannot, are useless if the data is bad or requires an update; that such memory can never be changed is a disadvantage in many applications, as bugs and security issues cannot be fixed, new features cannot be added. More ROM has come to include memory, read-only in normal operation, but can still be reprogrammed in some way. Erasable programmable read-only memory and electrically erasable programmable read-only memory can be erased and re-programmed, but this can only be done at slow speeds, may require special equipment to achieve, is only possible a certain number of times.
IBM used Capacitor Read Only Storage and Transformer Read Only Storage to store microcode for the smaller System/360 models, the 360/85 and the initial two models of the S/370. On some models there was a Writeable Control Store for additional diagnostics and emulation support; the simplest type of solid-state ROM is as old as the semiconductor technology itself. Combinational logic gates can be joined manually to map n-bit address input onto arbitrary values of m-bit data output. With the invention of the integrated circuit came mask ROM. Mask ROM consists of a grid of word lines and bit lines, selectively joined together with transistor switches, can represent an arbitrary look-up table with a regular physical layout and predictable propagation delay. In mask ROM, the data is physically encoded in the circuit, so it can only be programmed during fabrication; this leads to a number of serious disadvantages: It is only economical to buy mask ROM in large quantities, since users must contract with a foundry to produce a custom design.
The turnaround time between completing the design for a mask ROM and receiving the finished product is long, for the same reason. Mask ROM is impractical for R&D work since designers need to modify the contents of memory as they refine a design. If a product is shipped with faulty mask ROM, the only way to fix it is to recall the product and physically replace the ROM in every unit shipped. Subsequent developments have addressed these shortcomings. PROM, invented in 1956, allowed users to program its contents once by physically altering its structure with the application of high-voltage pulses; this addressed problems 1 and 2 above, since a company can order a large batch of fresh PROM chips and program them with the desired contents at its designers' convenience. The 1971 invention of EPROM solved problem 3, since EPROM can be reset to its unprogrammed state by exposure to strong ultraviolet light. EEPROM, invented in 1983, went a long way to solving problem 4, since an EEPROM can be programmed in-place if the containing device provides a means to receive the program contents from an external source.
Flash memory, invented at Toshiba in the mid-1980s, commercialized in the early 1990s, is a form of EEPROM that makes efficient use of chip area and can be erased and reprogrammed thousands of times without damage. All of these technologies improved the flexibility of ROM, but at a significant cost-per-chip, so that in large quantities mask ROM would remain an economical choice for many years. Rewriteable technologies were envisioned as replacements for mask ROM; the most recent development is NAND flash invented at Toshiba. Its designers explicitly broke from past practice, stating plainly that "the aim of NAND Flash is to replace hard disks," rather than the traditional use of ROM as a form of non-volatile primary storage; as of 2007, NAND has achieved this goal by offering throughput comparable to hard disks, higher tolerance of physical shock, extreme miniaturization, much lower power consumption. Every stored-program computer may use a form of non-volatile storage to store the initial program that runs when the computer is powered on or otherwise begins execution.
Every non-trivial computer needs some form of mutable memory to record changes in its state as it executes. Forms of read-only memory were employed as non-volatile storage for programs in most early stored-program computers, such as ENIAC after 1948. Read-only memory was simpler to implement since it needed only a mechanism to read stored values, not to change them in-place, thus could be implemented with crude electromechanical devices. With the advent of integrated circuits in the 1960s, both ROM and its mutable counterpart static RAM were implemented as arrays of transistors in silicon chips.
The Commodore 1541 is a floppy disk drive, made by Commodore International for the Commodore 64, Commodore's most popular home computer. The best-known floppy disk drive for the C64, the 1541 is a single-sided 170-kilobyte drive for 5¼" disks; the 1541 directly followed the Commodore 1540. The disk drive uses group coded recording and contains a MOS Technology 6502 microprocessor, doubling as a disk controller and on-board disk operating system processor; the number of sectors per track varies from 17 to 21. The drive's built-in disk operating system is CBM DOS 2.6. The 1541 was priced at under US$400 at its introduction. A C64 plus a 1541 cost about $900, while an Apple II with no disk drive cost $1295; the first 1541 drives produced in 1982 have a label on the front reading VIC-1541 and have an off-white case to match the VIC-20. In 1983, the 1541 was switched to having the familiar beige case and a front label reading "1541" along with rainbow stripes to match the Commodore 64. By 1983 a 1541 sold for $300 or less.
After a brutal home-computer price war that Commodore began, the C64 and 1541 together cost under $500. The drive became popular, became difficult to find; the company claimed that the shortage occurred because 90% of C64 owners bought the 1541 compared to its 30% expectation, but the press discussed what Creative Computing described as "an alarming return rate" because of defects. The magazine reported in March 1984 that it received three defective drives in two weeks, Compute!'s Gazette reported in December 1983 that four of the magazine's seven drives had failed. Publications sorely needs additional 1541s for in-house use. After numerous phone calls over several days, we were able to locate only two units in the entire continental United States" because of Commodore's attempt to resolve a manufacturing issue that caused the high failures; the early 1541s have a spring-eject mechanism, the disks fail to release. This style of drive has the popular nickname "Toaster Drive", because it requires the use of a knife or other hard thin object to pry out the stuck media just like a piece of toast stuck in an actual toaster.
This was fixed when Commodore changed the vendor of the drive mechanism and adopted the flip-lever Newtronics mechanism improving reliability. In addition, Commodore made the drive's controller board smaller and reduced its chip count compared to the early 1541s; the beige-case Newtronics 1541 was produced from 1984 to 1986. All but the earliest non-II model 1541s can use either the Alps or Newtronics mechanism. Visually, the first models, of the VIC-1541 denomination, have an off-white color like the VIC-20 and VIC-1540. To match the look of the C64, CBM changed the drive's color to brown-beige and the name to Commodore 1541; the 1541's numerous shortcomings opened a market for a number of third-party clones of the disk drive, a situation that continued for the lifetime of the C64. Well-known clones are the Oceanic OC-118 a.k.a. Excelerator+, the MSD Super Disk single and dual drives, the Enhancer 2000, the Indus GT, CMD's FD-2000 and FD-4000; the 1541 became the first disk drive to see widespread use in the home and Commodore sold millions of the units.
In 1986, Commodore released the 1541C, a revised version that offered quieter and more reliable operation and a light beige case matching the color scheme of the Commodore 64C. It was replaced in 1988 by the 1541-II, which uses an external power supply to provide cooler operation and allows the drive to have a smaller desktop footprint. ROM revisions fixed assorted problems, including a software bug that caused the save-and-replace command to corrupt data; the Commodore 1570 is an upgrade from the 1541 for use with the Commodore 128, available in Europe. It offers MFM capability for accessing CP/M disks, improved speed, somewhat quieter operation, but was only manufactured until Commodore got its production lines going with the 1571, the double-sided drive; the small, external-power-supply-based, MFM-based Commodore 1581 3½" drive was made, giving 800 KB access to the C128 and C64. The 1541 does not have DIP switches to change the device number. If a user added more than one drive to a system the user had to open the case and cut a trace in the circuit board to permanently change the drive's device number, or hand-wire an external switch to allow it to be changed externally.
It was possible to change the drive number via a software command, temporary and would be erased as soon as the drive was powered off. 1541 drives at power up always default to device #8. If multiple drives in a chain are used the startup procedure is to power on the first drive in the chain, alter its device number via a software command to the highest number in the chain power on the next drive, alter its device number to the next lowest, repeat the procedure until the final drive at the end of the chain was powered on and left as device #8. Unlike the Apple II, where support for two drives was normal, it was uncommon for Commodore software to support this setup, the CBM DOS copy file command was not able to copy files between drives--a third party copy utility must be used instead; the pre-II 1541s have an internal power source, which generate much heat. The
The Commodore 1581 is a 3½-inch double-sided double-density floppy disk drive, released by Commodore Business Machines in 1987 for its C64 and C128 home/personal computers. The drive stores 800 kilobytes using an MFM encoding but formats different from the MS-DOS, Mac Plus formats. With special software it's possible to read C1581 disks on an x86 PC system, read MS-DOS and other formats of disks in the C1581, provided that the PC or other floppy handles the "720 kB" size format; this capability was most used to read MS-DOS disks. The drive was released in the summer of 1987 and became popular with bulletin board system operators and other users. Like the 1541 and 1571, the 1581 has an onboard MOS Technology 6502 CPU with its own ROM and RAM, 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, 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.
The version of Commodore DOS built into the 1581 added support for partitions, which could function as fixed-allocation subdirectories. PC-style subdirectories were rejected as being too difficult to work with in terms of block availability maps still much in vogue, 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 1581 provides a total of 3160 blocks free; the number of permitted directory entries was increased, to 296 entries. With a storage capacity of 800 kB, the 1581 is the highest-capacity serial-bus drive, made by Commodore, the only 3½" one. However, starting in 1991, Creative Micro Designs made the FD-2000 high density and FD-4000 extra-high density 3½" drives, both of which offered not only a 1581-emulation mode but 1541- and 1571-compatibility modes. Like the 1541 and 1571, a nearly identical job queue is available to the user in zero page, 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 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; the WD1770 controller chip, was the seat of some early problems with 1581 drives when the first production runs were recalled due to a high failure rate. Versions of the 1581 drive have a smaller, more streamlined-looking external power supply provided with them; this article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later. The 1581 disk has each with 40 logical sectors; the directory starts on 40/3. The disk header is on 40/0, the BAM resides on 40/1 and 40/2.
Header Contents $00–01 T/S reference to first directory sector 02 DOS version 04-13 Disk Label, $A0 padded 16-17 Disk ID 19-1A DOS type BAM Contents, 40/1 $00–01 T/S to next BAM sector 02 DOS version 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 04-05 Disk ID 06 I/O byte 07 Autoboot flag 10-FF BAM entries for Tracks 41-80 Commodore 64 peripherals Commodore 128 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. Optusnet.com.au: 1581 Games, Commodore 1581 Games, D81, CMD FD2000 & FD4000 Games, Tools & Games for the 1581 disk drive. Optusnet.com.au: SEGA SF-7000 with PC 3.5" Floppy Drive, Copy disk to PC and vice versa, How to use a PC 3.5" floppy drive in the 1581 device vice-emu: Commodore compatible Disk Drives, drive info tut.fi: DCN-2692 floppy controller board, C1581 clone