Commodore 1541
Encyclopedia
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...
, was the best-known 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 for the Commodore 64
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...
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...
. The 1541 was a single-sided 170 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...
drive for 5¼" disks. The 1541 followed the previous Commodore 1540
Commodore 1540
The Commodore 1540 was the companion floppy disk drive for the Commodore VIC-20 home computer. It used single-sided 5¼" floppy disks, on which it stored roughly 170 KB of data utilizing Commodore's GCR data encoding scheme.Because of the low price of both the VIC-20 and the 1540, this...
(meant for the VIC-20
Commodore VIC-20
The VIC-20 is an 8-bit home computer which was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the PET...
).
The disk drive used Group Code Recording
Group Code Recording
In computer science, group code recording refers to several distinct but related encoding methods for magnetic media. The first, used in 6250 cpi magnetic tape, is an error-correcting code combined with a run length limited encoding scheme...
(GCR) and contained a MOS
MOS Technology
MOS Technology, Inc., also known as CSG , was a semiconductor design and fabrication company based in Norristown, Pennsylvania, in the United States. It is most famous for its 6502 microprocessor, and various designs for Commodore International's range of home computers.-History:MOS Technology, Inc...
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...
microprocessor, doubling as a disk controller
Disk controller
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card...
and on-board disk operating system
Disk operating system
Disk Operating System and disk operating system , most often abbreviated as DOS, refers to an operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them...
processor. The number of sectors per track varied from 17 to 21 (an early implementation of Zone Bit Recording
Zone bit recording
Zone Bit Recording is used by disk drives to store more sectors per track on outer tracks than on inner tracks. It is also called Zone Constant Angular Velocity ....
). The drive's built-in disk operating system was CBM DOS 2.6
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...
.
Disk capacity
Each side of 170 kBKilobyte
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 was split into 683 sectors on 35 tracks, each of the sectors holding 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 file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
made each sector individually rewritable.
However, one track was reserved by DOS for directory and file allocation information (so-called BAM, Block Allocation Map
Block allocation map
In computer file systems, a block allocation map is a data structure used to track disk blocks that are considered "allocated" or "free for writing."...
). And since for normal files, two bytes of each physical sector were used by DOS as a pointer to the next physical track and sector of the file, only 254 out of the 256 bytes of a block were used for file contents.
If the disk was not otherwise prepared with a custom format, (e.g. for data disks), 664 blocks would be free after formatting, giving 664 × 254 = 168,656 bytes (or almost 165 kB) for user data.
By using custom formatting and load/save routines (sometimes included in third-party DOSes, see below), all of the mechanically possible 40 tracks could be used. The reason why Commodore decided not to use the upper five tracks by default (or at least more than 35) was the bad quality of some of the drive mechanisms which did not always work reliably at the highest tracks. So by reducing the number of tracks used and thus capacity, it was possible to further reduce cost - in contrast to Double Density drives used e.g. in IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
computers of the day which saved 180 kB on one side (by using a 40 tracks format).
The 1541 did not have an index hole sensor, making it straightforward to use the reverse side of a disk by flipping it. A disc could be converted to a "flippy disk
Flippy disk
A flippy disk is a double-sided 5¼" floppy disk, specially modified so that the two sides can be used independently in single-sided drives...
" by simply cutting/punching a notch on the left-hand side, causing the drive to recognize both sides as writable. This would effectively double the storage capacity. The notch could be made with a scissors
Scissors
Scissors are hand-operated cutting instruments. They consist of a pair of metal blades pivoted so that the sharpened edges slide against each other when the handles opposite to the pivot are closed. Scissors are used for cutting various thin materials, such as paper, cardboard, metal foil, thin...
, knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...
, hole punch
Hole punch
A hole punch is a common office tool that is used to create holes in sheets of paper, often for the purpose of collecting the sheets in a binder or folder.The origins of the hole punch date back to Germany via Matthias Theel, where two early patents for a...
, or "disk notcher" tool that was specifically designed for this task. Most soft sectored and all hard sectored drives would have also required an extra cut-out for the index hole — a harder modification.
| Track | Sectors (256 bytes) | bits/s |
|---|---|---|
| 1 - 17 | 21 | 16M/4/(13+0) = 307 692 |
| 18 - 24 | 19 | 16M/4/(13+1) = 285 714 |
| 25 - 30 | 18 | 16M/4/(13+2) = 266 667 |
| 31 - 35 | 17 | 16M/4/(13+3) = 250 000 |
| 36 - 42 | 17 | 16M/4/(13+3) = 250 000 |
Tracks 36-42 are non standard.
The bitrate is after GCR encoding, so actual data is a factor 5/4 less.
1541 Image Layout
Tracks 1-17 are for data, as are tracks 19-35. Track 18 is reserved for the directory and the disk header. . The directory starts on 18/1 (track 18, sector 1). The header is on 18/0, and the BAM (Block Allocation Map) resides on 18/0 as well.Header Contents
$00-01 T/S reference to first directory sector (18/1)
02 DOS version ('A')
04-8F BAM entries (4 bytes per track: Free Sector Count + 24 bits for sectors)
90-9F Disk Label, $A0 padded
A2-A3 Disk ID
A5-A6 DOS type ('2A')
Introduction and early problems
Priced at under US$United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
400 at its introduction, the 1541 became widely popular. Although expensive by today's standards, a C64 plus a 1541 cost about $900, while an Apple II with no disk drive cost $1395. The demand caught Commodore by surprise, and they struggled to produce the drive in adequate quantities.
Failure rates on the 1541 initially were very high, and the drives were virtually impossible to find. The lead editorial in the December 1983 issue of Compute!'s Gazette
COMPUTE!'s Gazette
COMPUTE!'s Gazette was a computer magazine of the 1980s, directed at users of Commodore's 8-bit home computers. Publishing its first issue in July 1983, the Gazette was a Commodore-only daughter magazine of the computer hobbyist magazine COMPUTE!....
lamented that four of the seven drives the magazine had in its editorial offices had failed. Eventually the problems subsided and the drive became nearly as widely available as the C64 itself.
The 1541 did not have dip switches to change the drive 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 number, or hand-wire an external switch to allow it to be changed externally. It was also possible to change the number temporarily from the operating system.
The 1541 also had an internal power source, which generated some heat. The heat generation was a frequent source of humour. For example, series of humorous tips in MikroBitti
MikroBitti
MikroBitti is a Finnish computer magazine, founded in May 1984 and published by Sanoma Magazines, a division of the Sanoma Group. MikroBitti is aimed mainly for beginner to mid-level computer users...
5/1989 said "When programming late, coffee
Coffee
Coffee is a brewed beverage with a dark,init brooo acidic flavor prepared from the roasted seeds of the coffee plant, colloquially called coffee beans. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia,...
and kebab
Kebab
Kebab is a wide variety of meat dishes originating in Middle East and later on adopted by the Middle East, and Asia Minor, and now found worldwide. In English, kebab with no qualification generally refers more specifically to shish kebab served on the skewer...
keep nicely warm on top of the 1541." The MikroBitti review of the 1541-II said that its external power source "should end the jokes about toasters".
The early 1541's had a spring eject mechanism (Alps Drive), and the discs often failed to release. This style of drive had the popular nickname "Toaster Drive", because it required the use of a knife or other thin object to pry out the stuck media just like a piece of toast stuck in a real toaster (though this is inadvisable with real toasters). This was fixed later, when Commodore changed the vendor of the drive mechanism (Mitsumi
Mitsumi
is a Japanese manufacturer of consumer electronic components, founded in 1954.-Products:One of the company's most noticeable product lines are video game console controllers...
) and went to a flip handle that allowed extraction of the disc using your fingers, and no longer requiring the spring.
Versions and third-party clones
Mitsumi
is a Japanese manufacturer of consumer electronic components, founded in 1954.-Products:One of the company's most noticeable product lines are video game console controllers...
), which used a lever release. All but the very earliest 1541s can use either the Alps or Newtronics mechanism. Visually, the first models, of the VIC-1541 denomination, had an off-white color like the VIC-20 and VIC-1540. Then, to match the look of the C64, 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...
changed the drive's color to brown-beige and the name to Commodore 1541.
MSD Super Disk
The MSD Super Disk was a series of floppy disk drives produced by Micro Systems Development for use with Commodore 8-bit home computers. Two different versions of the MSD Super Disk were available: the single-drive SD-1 and the dual-drive SD-2....
single and dual drives, the Enhancer 2000, the Indus GT
Indus GT
The Indus GT was a floppy disk drive made by Indus Systems of California, USA during the early 1980s for Commodore, Apple II series and Atari home computer platforms of the day. It came in a black casing with a smoke plexiglas cover over the drive mechanism. Behind the cover was an 8 segment LED...
, and 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....
's FD-2000 and FD-4000. Nevertheless, 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 slightly 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 used an external power supply to provide cooler operation and allow the drive to have a smaller desktop footprint (the power supply "brick" being placed elsewhere, typically on the floor).
The serial computer interface
The 1541 used a proprietary bit-serial derivative of the standardized IEEE-488IEEE-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...
parallel interface, which was used on Commodore's earlier drives for the PET/CBM
Commodore PET
The Commodore PET was a home/personal computer produced from 1977 by Commodore International...
range of personal/business computers. To ensure a ready supply of inexpensive cabling for its home computer peripherals, Commodore chose standard DIN connector
DIN connector
A DIN connector is a connector that was originally standardized by the , the German national standards organization. There are DIN standards for a large number of different connectors, therefore the term "DIN connector" alone does not unambiguously identify any particular type of connector unless...
s for the serial interface. Disk drives and other peripherals such as printers were connected to the computer via a daisy chain
Daisy chain (electrical engineering)
In electrical and electronic engineering a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring...
scheme, necessitating only a single connector on the computer itself.
Initially, Commodore intended to use a hardware shift register (one component of the 6522 VIA
MOS Technology 6522
The 6522 Versatile Interface Adapter was an integrated circuit made by MOS Technology, as well as second sources including Rockwell and Synertek. It served as a I/O port controller for the 6502 family of microprocessors, providing the parallel I/O capabilities of the PIA as well as timers and a...
) to maintain relatively brisk drive speeds with the new serial interface. However, a hardware bug with this chip prevented the initial design from working as anticipated, and the ROM code was hastily rewritten to handle the entire operation in software. According to Jim Butterfield
Jim Butterfield
-External links:* * featuring Brad Templeton, Jim Butterfield, and Steve Punter** * * , previous unpublished, presented by the Personal Computer Museum, Brantford, Ontario...
, this caused a speed reduction by a factor of five.
As implemented on the VIC-20 and Commodore 64
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...
, CBM 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...
could transfer only about 300 bytes per second, which translated to about 20 minutes to copy one disk—10 minutes of reading time, and 10 minutes of writing time. However, since both the computer and the drive could easily be reprogrammed, third parties quickly wrote more efficient firmware that would speed up drive operations drastically. Without hardware modifications, some "fast loader
Fast loader
A fast loader is a software program for a home computer - most commonly, the Commodore 64 - that accelerates the speed of file loading from the floppy disk drive.- Background :...
" utilities managed to achieve speeds of up to 4 kB/s. The most common of these products were the Epyx FastLoad
Epyx FastLoad
The Epyx FastLoad is a floppy disk fast loader cartridge made by American software company Epyx in 1984 for the Commodore 64 home computer. It was programmed by Epyx employee Scott Nelson, who later designed the Epyx Vorpal fastloading system for the company's games.Epyx FastLoad allowed programs...
, the Final Cartridge
The Final Cartridge III
The Final Cartridge III was a popular extension cartridge which was created for the Commodore 64 and Commodore 128, produced by Riska B.V. Home & Personal Computers...
, and the Action Replay plug-in cartridges, which all had machine code monitor
Machine code monitor
A machine code monitor is software built into or separately available for various computers, allowing the user to enter commands to view and change memory locations on the machine, with options to load and save memory contents from/to secondary storage.Machine code monitors became something of a...
and disk editor
Disk editor
A disk editor is a computer program that allows its user to read, edit, and write raw data on disk drives ; as such, they are sometimes called sector editors, since the read/write routines built into the electronics of most disk drives require to read/write data in...
software on board as well. The popular Commodore computer magazines of the era also entered the arena with type-in fast-load utilities, with Compute!'s Gazette
COMPUTE!'s Gazette
COMPUTE!'s Gazette was a computer magazine of the 1980s, directed at users of Commodore's 8-bit home computers. Publishing its first issue in July 1983, the Gazette was a Commodore-only daughter magazine of the computer hobbyist magazine COMPUTE!....
publishing TurboDisk in 1985 and RUN publishing Sizzle in 1987.
Even though each 1541 had its own on board disk controller and disk 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...
, it was not possible for a user to command two 1541 drives to copy a disk (one drive reading and the other writing) as with older dual drives like the 4040
Commodore 4040
The Commodore 4040 and its sibling, the 2040 and the European marketed 3040, were dual unit 5¼" floppy disk drives for Commodore International computers...
and 8050
Commodore 8050
The Commodore 8050 and Commodore 8250 were dual unit 5¼" floppy disk drives for Commodore International computers. They used a wide rectangular steel case form similar to that of the Commodore 4040, and used the IEEE-488 interface common to Commodore PET/CBM computers.The 8050 was a single...
that were often found with the PET computer, and which the 1541 was backward compatible to (it could read 4040 disks but not write to them since its internal Operating System was essentially the same). Unfortunately, however, the routines in the 1541 disk operating system to enable disk copy were removed as it was intended to be a stand-alone unit. To copy from drive to drive, software running on the C64 was needed and it would first read from one drive into memory, then write out to the other. Only later when first Fast Hack'em
Fast Hack'em
Fast Hack'em was a Commodore 64 nibbler and disk editor written by Mike J. Henry and released in 1985. It was distributed in the U.S. via Henry's "Basement Boys Software", and in the U.K. via Datel Electronics. In the U.S., it retailed for $29.95.-Features:...
then other disk backup programs were released was true drive to drive copying possible. One could then (in theory at least) unplug the C64 itself from the drives (i.e. from the first drive in the daisy chain) and do something else with the computer as the drives proceeded to copy the entire disk. This is not a recommended practice as disconnecting the serial lead from a powered drive and/or computer could result in destruction of one or both of the port chips in the disk drive.
Copy protection by read error
Early copy protectionCopy protection
Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...
schemes deliberately introduced read errors on the disk, the software refusing to load unless the correct error message was returned. The general idea was that simple disk copy programs were incapable of copying the errors. When one of these errors was encountered, the disk drive (as do all disk drives) would attempt one or more re-read attempts after first resetting the head to track zero. Few of these schemes had much deterrent effect, as various software companies soon released "nibbler" utilities that enabled protected disks to be copied and, in some cases, the protection removed.
The drive head misalignment issue
The drive-head mechanism was notoriously easy to misalign, and had a tendency to make a "machine-gun" rattle when out of alignment or when formatting a new disk. Some people even wrote code to vibrate the head at different frequencies to play simple tunes such as "Daisy BellDaisy Bell
"Daisy Bell" is a popular song with the well-known chorus "Daisy, Daisy/Give me your answer do/I'm half crazy/all for the love of you" as well as the line "...a bicycle built for two".-History:"Daisy Bell" was composed by Harry Dacre in 1892...
", "Amazing Grace
Amazing Grace
"Amazing Grace" is a Christian hymn with words written by the English poet and clergyman John Newton , published in 1779. With a message that forgiveness and redemption are possible regardless of the sins people commit and that the soul can be delivered from despair through the mercy of God,...
", and, perhaps most appropriately, "When I'm Sixty-Four
When I'm Sixty-Four
"When I'm Sixty-Four" is a song by The Beatles, written by Paul McCartney and released in 1967 on their album Sgt. Pepper's Lonely Hearts Club Band.-Composition:...
". The most common cause of the 1541's drive head knocking and subsequent misalignment, however, was copy protection schemes on commercial software.
The main cause of the problem was that the disk drive itself did not feature any means of detecting when the read/write head had reached track zero. Accordingly, when a disk was formatted or a disk error occurred, the unit would try to physically move the head 40 times in the direction of track zero (although the 1541 DOS only used 35 tracks, the drive itself was a 40 track unit, so this ensured track zero would be reached no matter where the head was before). Once track zero was reached, every further attempt to move the head in that direction would cause it to be physically rammed against a solid stop - e.g. if the head happened to be on track 18 before this procedure, the head would be actually moved 18 times, and then rammed against the stop another 22 times. This ramming gave the characteristic "machine gun" noise and would, sooner or later, throw the head out of alignment.
There were at least one or two "home remedy" software products on the market during the heyday of the 1541 drive and Commodore 64 computer that could be used to re-align the drive yourself and save a costly trip to a repair center and down time. They generally consisted of a software program and a calibration disk. What the user would do is remove the drive from its case and then loosen the screws holding the stepper motor that moved the head. Then with the calibration disk in the drive gently turn the stepper motor back and forth until the program showed a good alignment. The screws were then tightened and the drive put back into its case. The real problem actually was that the sprocket which moved the head would slip on the stepper motor shaft after repeated hammering and this would put the drive gradually out of alignment.
The later 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...
drive (which was 1541 compatible) incorporated track zero detection by photo-interrupter and was thus immune to the problem. A third-party fix for the 1541 appeared where the solid head stop was replaced by a sprung stop, giving the head a much easier life. Also, a software solution, which resided in the drive controller's ROM, could prevent the re-reads from occurring, though this could cause problems when genuine errors did occur.
Commodore's successor products
The Commodore 1570Commodore 1570
The Commodore 1570 was a 5¼" floppy disk drive for the Commodore 128 home/personal computer. It was a single-sided, 170KB version of the double-sided Commodore 1571, released as a stopgap measure when Commodore International was unable to provide large enough quantities of 1571s due to a shortage...
was an upgraded 1541 for use with the Commodore 128
Commodore 128
The Commodore 128 home/personal computer was the last 8-bit machine commercially released by Commodore Business Machines...
, available in Europe. It offered 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...
capability for accessing CP/M disks, improved speed, and somewhat quieter operation, but was only manufactured until Commodore got its production lines going with the double-sided 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...
. Finally, the small, external power supply, MFM-based 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 was made, giving 800 KB access to the C128 and C64. By this time, however, many CBM users had shifted their attention to the 16/32-bit 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...
, and the 1581 was mostly sold to remaining 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...
users.
External links
- C64 Preservation Project Discusses internal drive mechanics and copy protection
- Undocumented 1541 drive functions – From the Project 64 website