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68-455: Like the 1541 and 1571 , 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

136-401: 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 (an early implementation of zone bit recording with 4 constant angular velocity zones ). 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 with

204-454: A cyclic redundancy check (CRC) replacing parity per character detection of prior generations. These IBM physical records have three basic parts, a Count field which acts as an ID field, an optional Key field to aid in searching for data and a Data field; in practice, most records had no Key field, indicated by a key length of zero. The structure of these three fields is called the CKD track format for

272-500: A proprietary serialized derivative of the IEEE-488 parallel interface, found in previous disk drives for the PET/CBM range of personal and business computers, but when the VIC-20 was in development, a cheaper alternative to the expensive IEEE-488 cables was sought. To ensure a ready supply of inexpensive cabling for its home computer peripherals, Commodore chose standard DIN connectors for

340-499: A 1541 cost about $ 900, while an Apple II with no disk drive cost $ 1,295. The first 1541 drives produced in 1982 have a label on the front reading VIC-1541 and an off-white case to match the VIC-20. In 1983, the 1541 switched to the familiar beige case and a front label reading simply "1541" along with rainbow stripes to match the Commodore 64. By 1983, a 1541 sold for $ 300 or less. After a home computer price war instigated by Commodore,

408-482: A favorite with amateur and professional chefs since they could compute and cook on top of their 1500-series disk drives at the same time". A series of humorous tips in MikroBitti in 1989 said "When programming late, coffee and kebab 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 drive-head mechanism installed in

476-464: A future IDEMA standard, Samsung and Toshiba began shipments of 1.8-inch hard disk drives with 4096 byte sectors. In 2010 IDEMA completed the Advanced Format standard for 4096 sector drives, setting the date for the transition from 512 to 4096 byte sectors as January 2011 for all manufacturers, and Advanced Format drives soon became prevalent. While sector specifically means the physical disk area,

544-459: A hardware shift register (one component of the 6522) to maintain fast drive speeds with the new serial interface . However, a hardware bug with this chip prevents 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 , this causes a speed reduction by a factor of five; had 1540 compatibility not been

612-427: A larger cluster size reduces bookkeeping overhead and fragmentation, which may improve reading and writing speed overall. Typical cluster sizes range from 1 sector (512 B) to 128 sectors (64 KiB ). A cluster need not be physically contiguous on the disk; it may span more than one track or, if sector interleaving is used, may even be discontiguous within a track. This should not be confused with fragmentation , as

680-470: A lever rather than a pull-down tab to close the drive door. Although the alignment issues were resolved after the switch, the Newtronics drives add a new reliability problem in that many of the read/write heads are improperly sealed, causing moisture to penetrate the head and short it out. The 1541's PCB consists mainly of a 6502 CPU, two 6522 VIA chips, and 2k of work RAM. Up to 48k of RAM can be added; this

748-484: A record. The 1970 IBM 3330 disk storage replaced the CRC on the data field of each record with an error correcting code (ECC) to improve data integrity by detecting most errors and allowing correction of many errors. Ultimately all fields of disk sectors had ECCs. Prior to the 1980s, there was little standardization of sector sizes; disk drives had a maximum number of bits per track and various system manufacturers subdivided

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816-606: A requirement, the disk interface would have been much faster. In any case, the C64 normally cannot work with a 1540 unless the VIC-II display output is disabled via a register write to the DEN bit (register $ D011, bit 4), which stops the halting of the CPU during certain video lines to ensure correct serial timing. As implemented on the VIC-20 and C64, Commodore DOS transfers 512 bytes per second, compared to

884-466: A small number of contiguous tracks. Each zone is then divided into sectors such that each sector has a similar physical size. Because outer zones have a greater circumference than inner zones, they are allocated more sectors. This is known as zoned bit recording . A consequence of zone bit recording is that contiguous reads and writes are noticeably faster on outer tracks (corresponding to lower block addresses) than on inner tracks, as more bits pass under

952-493: A spring-eject mechanism ( Alps drive), and the disks often 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 later when Commodore changed the vendor of the drive mechanism ( Mitsumi ) and adopted the flip-lever Newtronics mechanism, greatly improving reliability. In addition, Commodore made

1020-475: Is 1541-compatible) incorporates track-zero detection by photo-interrupter and is thus immune to the problem. Also, a software solution, which resides in the drive controller's ROM, prevents the rereads from occurring, though this can cause problems when genuine errors do occur. Due to the alignment issues on the Alps drive mechanisms, Commodore switched suppliers to Newtronics in 1984. The Newtronics mechanism drives have

1088-476: Is a factor 5/4 less due to GCR encoding . The 1541 disk typically has 35 tracks. Track 18 is reserved; the remaining tracks are available for data storage. The header is on 18/0 (track 18, sector 0) along with the BAM, and the directory starts on 18/1 (track 18, sector 1). The file interleave is 10 blocks, while the directory interleave is 3 blocks. Header contents: The header is similar to other Commodore disk headers,

1156-399: Is a unit of disk space allocation for files and directories. To reduce the overhead of managing on-disk data structures, the filesystem does not allocate individual disk sectors by default, but contiguous groups of sectors, called clusters. On a disk that uses 512-byte sectors, a 512-byte cluster contains one sector, whereas a 4- kibibyte ( KiB ) cluster contains eight sectors. A cluster is

1224-507: Is detected. The tape version will even crash if a floppy drive is switched on while the game is running. Disk sector In computer disk storage , a sector is a subdivision of a track on a magnetic disk or optical disc . For most disks, each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs), and 2048 bytes for CD-ROMs , DVD-ROMs and BD-ROMs . Newer HDDs and SSDs use 4096 byte (4  KiB ) sectors, which are known as

1292-449: Is mainly useful for defeating copy protection schemes since an entire disk track could be loaded into drive RAM, while the standard 2k only accommodates a few sectors (theoretically eight, but some of the RAM was used by CBM DOS as work space). Some Commodore users use 1541s as an impromptu math coprocessor by uploading math-intensive code to the drive for background processing . The 1541 uses

1360-499: Is 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 that was often found with the PET computer, and which the 1541 is backward-compatible with (it can read 4040 disks but not write to them as a minor difference in the number of header bytes makes the 4040 and 1541 only read-compatible). Originally, to copy from drive to drive, software running on

1428-410: 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

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1496-443: Is similar to the format used on the PET 2031, 2040 & 4040 drives, but a minor difference in the number of header bytes makes these drives and the 1541 only read-compatible; disks formatted with one drive cannot be written to by the other. The drives will allow writes to occur, but the inconsistent header size will damage the data in the data portions of each track. The 4040 drives use Shugart SA-400s, which were 35-track units, thus

1564-409: 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 (if three drives were used, then the first drive in the chain would be set to device #10), then power on the next drive, alter its device number to the next lowest, and repeat the procedure until the final drive at the end of the chain was powered on and left as device #8. Unlike

1632-559: The 1541 and 1571 , a nearly identical job queue 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 FM/MFM floppy controller chip. The 1581 disk format consists of 80 tracks and ten 512 byte sectors per track, per side, used as 40 logical sectors of 256 bytes each. Special software

1700-443: The Advanced Format (AF). The sector is the minimum storage unit of a hard drive. Most disk partitioning schemes are designed to have files occupy an integral number of sectors regardless of the file's actual size. Files that do not fill a whole sector will have the remainder of their last sector filled with zeroes. In practice, operating systems typically operate on blocks of data , which may span multiple sectors. Geometrically,

1768-556: The Apple II , where support for two drives is normal, it is relatively uncommon for Commodore software to support this setup, and the CBM DOS copy file command is not able to copy files between drives – a third party copy utility is necessary. The pre-II 1541s also have an internal power source, which generates a lot of heat. The heat generation was a frequent source of humour. For example, Compute! stated in 1988 that "Commodore 64s used to be

1836-709: The Atari 810 's 1,000 bytes per second, the Apple Disk II 's 15,000 bytes per second, and the 300- baud data rate of the Commodore Datasette storage system. About 20 minutes are needed to copy one disk—10 minutes of reading time, and 10 minutes of writing time. However, since both the computer and the drive can easily be reprogrammed, third parties quickly wrote more efficient firmware that would speed up drive operations drastically. Without hardware modifications, some " fast loader " utilities (which bypassed routines in

1904-564: The CBM 1541 and VIC-1541 ) is a floppy disk drive which was made by Commodore International for the Commodore 64 (C64), 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 (meant for the VIC-20 ). The disk drive uses group coded recording (GCR) and contains

1972-415: 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 offers 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 uses an external power supply to provide cooler operation and allows

2040-804: The 1541's onboard ROM) managed to achieve speeds of up to 4 kbit/s. The most common of these products are the Epyx Fast Load , the Final Cartridge , and the Action Replay plug-in ROM cartridges , which all have machine code monitor and disk editor 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 publishing TurboDisk in 1985 and RUN publishing Sizzle in 1987. Even though each 1541 has its own on-board disk controller and disk operating system, it

2108-472: 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 high density (1.6 MB) and FD-4000 extra-high density (3.2 MB) 3½" drives, both of which offered not only a 1581-emulation mode but also 1541- and 1571-compatibility modes. Like

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2176-596: The C64 and 1541 together cost under $ 500. The drive became very popular and difficult to find. The company said 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 absolutely alarming return rate" because of defects. The magazine reported in March 1984 that it received three defective drives in two weeks, and Compute!'s Gazette reported in December 1983 that four of

2244-403: The C64 was needed and it would first read from one drive into computer memory, then write out to the other. Only when Fast Hack'em and, later, other disk backup programs were released, was true drive-to-drive copying possible for a pair of 1541s. The user could, if they wished, unplug the C64 from the drives (i.e., from the first drive in the daisy chain) and do something else with the computer as

2312-503: 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 built into the 1581 added support for partitions , 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, which were still very much in vogue, and which for some time had been

2380-458: The IBM FBA DASD supported sector sizes of 512, 1024, 2048, or 4096 bytes. In 2000 the industry trade organization, International Disk Drive Equipment and Materials Association ( IDEMA ) started work to define the implementation and standards that would govern sector size formats exceeding 512 bytes to accommodate future increases in data storage capacities. By the end of 2007 in anticipation of

2448-700: The VIC-20 and VIC-1540. Then, 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. Examples include the Oceanic OC-118 a.k.a. Excelerator+ , the MSD Super Disk single and dual drives, the Enhancer 2000 , the Indus GT , Blue Chip Electronics 's BCD/5.25, and CMD ' s FD-2000 and FD-4000 . Nevertheless,

2516-453: The block size to be used during execution with the parameter bs=bytes . This specifies the size of the chunks of data as delivered by dd, and is unrelated to sectors or filesystem blocks. In Linux, disk sector size can be determined with sudo fdisk -l | grep "Sector size" and block size can be determined with sudo blockdev --getbsz /dev/sda . In computer file systems , a cluster (sometimes also called allocation unit or block )

2584-457: The business market with the Apple and perhaps with other business computers. With the present disk drive, though, it is hard-pressed to lose its image as a toy. The C-64's designers blamed the 1541's slow speed on the marketing department's insistence that the computer be compatible with the 1540, which is slow because of a flaw in the 6522 VIA interface controller. Initially, Commodore intended to use

2652-408: 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 is also possible to change the drive number via a software command, which is 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, then the startup procedure

2720-630: The concept of zoned recording (ZBR) which allowed the number of sectors per track to vary as a function of the track's diameter – there are more sectors on an outer track than on an inner track. In the late 1980s ZBR was again used in disk drives then announced by Imprimis and Quantum and by 1997 its industry usage was ubiquitous. The disk drives and other DASDs announced with the IBM System/360 in 1964 used self-formatting variable length sectors, termed records or physical records by IBM. They detected errors in all fields of their records with

2788-435: The correct location. The data area contains the sync bytes, user data and an error-correcting code (ECC) that is used to check and possibly correct errors that may have been introduced into the data. The first disk drive, the 1957 IBM 350 disk storage , had ten 100 character sectors per track; each character was six bits and included a parity bit. The number of sectors per track was identical on all recording surfaces. There

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2856-423: The data area. The sector header contains information used by the drive and controller; this information includes sync bytes, address identification , flaw flag and error detection and correction information. The header may also include an alternate address to be used if the data area is undependable. The address identification is used to ensure that the mechanics of the drive have positioned the read/write head over

2924-403: The directory is located) before this procedure, the head would be actually moved 18 times, and then rammed against the stop 22 times. This ramming gives the characteristic "machine gun" noise and sooner or later throws the head out of alignment. A defective head-alignment part likely caused many of the reliability issues in early 1541 drives; one dealer told Compute! ' s Gazette in 1983 that

2992-673: The disk. However, one track is reserved by DOS for directory and file allocation information (the BAM, block availability map ). And since for normal files, two bytes of each physical sector are 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 are used for file contents. If the disk side is 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

3060-511: The drive to have a smaller desktop footprint (the power supply "brick" being placed elsewhere, typically on the floor). Later ROM revisions fixed assorted problems, including a software bug that causes 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, and somewhat quieter operation, but

3128-477: The drive's controller board smaller and reduced its chip count compared to the early 1541s (which had a large PCB running the length of the case, with dozens of TTL chips ). The beige-case Newtronics 1541 was produced from 1984 to 1986. All but the very 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

3196-464: The drives proceeded to copy the entire disk. The 1541 drive uses standard 5¼-inch double-density floppy media; high-density media will not work due to its different magnetic coating requiring a higher magnetic coercivity . As the GCR encoding scheme does not use the index hole, the drive was also compatible with hard-sectored disks. The standard CBM DOS format is 170 KB with 35 tracks and 256-byte sectors. It

3264-410: The early production years is notoriously easy to misalign. The most common cause of the 1541's drive head knocking and subsequent misalignment is copy-protection schemes on commercial software. The main cause of the problem is that the disk drive itself does not feature any means of detecting when the read/write head reaches track zero. Accordingly, when a disk is not formatted or a disk error occurs,

3332-435: The format there is due to physical limitations of the drive mechanism. The 1541 uses 40 track mechanisms, but Commodore intentionally limited the CBM DOS format to 35 tracks because of reliability issues with the early units. It is possible via low-level programming to move the drive head to tracks 36–40 and write on them, this is sometimes done by commercial software for copy protection purposes and/or to get additional data on

3400-474: The head to track zero. Few of these schemes have much deterrent effect, as various software companies soon released " nibbler " utilities that enable protected disks to be copied and, in some cases, the protection removed. Commodore copy protection sometimes fails on specific hardware configurations. Gunship , for example, does not load if a second disk drive or printer is connected to the computer. Similarly Roland's Ratrace will crash if additional hardware

3468-400: The head with each rotation; this difference can be 25% or more. In 1998 the traditional 512-byte sector size was identified as one impediment to increasing capacity which at that time was growing at a rate exceeding Moore's Law . Increasing the length of the data field through the implementation of Advanced Format using 4096-byte sectors removed this impediment; it increased the efficiency of

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3536-414: The magazine's seven drives had failed; "COMPUTE! Publications sorely needs additional 1541s for in-house use, yet we can't find any to buy. After numerous phone calls over several days, we were able to locate only two units in the entire continental United States ", reportedly because of Commodore's attempt to resolve a manufacturing issue that caused the high failures. The early (1982 to 1983) 1541s have

3604-442: The mechanically possible 40 tracks can be used. Owing to the drive's non-use of the index hole, it is also possible to make " flippy floppies " by inserting the diskette upside-down and formatting the other side, and it is commonplace and normal for commercial software to be distributed on such disks. Tracks 36–42 are non-standard. The bitrate is the raw one between the read/write head and signal circuitry so actual useful data rate

3672-420: The part had caused all but three of several hundred drive failures that he had repaired. The drives were so unreliable that Info magazine joked, "Sometimes it seems as if one of the original design specs ... must have said ' Mean time between failure : 10 accesses.'" Users can realign the drive themselves with a software program and a calibration disk. The user can remove the drive from its case and then loosen

3740-430: The screws holding the stepper motor that move the head, then with the calibration disk in the drive gently turn the stepper motor back and forth until the program shows a good alignment. The screws are then tightened and the drive is put back into its case. A third-party fix for the 1541 appeared in which the solid head stop was replaced by a sprung stop, giving the head a much easier life. The later 1571 drive (which

3808-510: The sectors are still logically contiguous. A "lost cluster" occurs when a file is deleted from the directory listing, but the File Allocation Table (FAT) still shows the clusters allocated to the file. The term cluster was changed to allocation unit in DOS 4.0. However the term cluster is still widely used. If a sector is defined as the intersection between a radius and a track, as

3876-466: The serial interface. Disk drives and other peripherals such as printers connect to the computer via a daisy chain setup, necessitating only a single connector on the computer itself. IEEE Spectrum in 1985 stated that: The one major flaw of the C-64 is not in the machine itself, but in its disk drive. With a reasonably fast disk drive and an adequate disk-operating system (DOS), the C-64 could compete in

3944-432: The smallest logical amount of disk space that can be allocated to hold a file. Storing small files on a filesystem with large clusters will therefore waste disk space; such wasted disk space is called slack space . For cluster sizes which are small versus the average file size, the wasted space per file will be statistically about half of the cluster size; for large cluster sizes, the wasted space will become greater. However,

4012-503: The structural differences being the BAM offset ( $ 04 ) and size, and the label+ID+type offset ( $ 90 ). Early copy protection schemes deliberately introduce read errors on the disk, the software refusing to load unless the correct error message is returned. The general idea is that simple disk-copy programs are incapable of copying the errors. When one of these errors is encountered, the disk drive (as do many floppy disk drives) will attempt one or more reread attempts after first resetting

4080-451: The term block has been used loosely to refer to a small chunk of data. Block has multiple meanings depending on the context. In the context of data storage, a filesystem block is an abstraction over disk sectors possibly encompassing multiple sectors. In other contexts, it may be a unit of a data stream or a unit of operation for a utility. For example, the Unix program dd allows one to set

4148-558: The track into different sector sizes to suit their OSes and applications. The popularity of the PC beginning in the 1980s and the advent of the IDE interface in the late 1980s led to a 512-byte sector becoming an industry standard sector size for HDDs and similar storage devices. In the 1970s, IBM added fixed-block architecture Direct Access Storage Devices (FBA DASDs) to its line of CKD DASD. CKD DASD supported multiple variable length sectors while

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4216-458: 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 when formatted (a block being equal to 256 bytes ). The number of permitted directory entries was also increased, to 296 entries. With a storage capacity of 800 kB,

4284-438: The unit tries to move the head 40 times in the direction of track zero (although the 1541 DOS only uses 35 tracks, the drive mechanism itself is a 40-track unit, so this ensured track zero would be reached no matter where the head was before). Once track zero is reached, every further attempt to move the head in that direction would cause it to be rammed against a solid stop: for example, if the head happened to be on track 18 (where

4352-403: The word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), which is shaped like a slice of a pie. Thus, the disk sector (Figure 1, item C) refers to the intersection of a track and geometrical sector . In modern disk drives, each physical sector is made up of two basic parts, the sector header area (typically called "ID") and

4420-431: Was no recorded identifier field (ID) associated with each sector. The 1961 IBM 1301 disk storage introduced variable length sectors, termed records or physical records by IBM, and added to each record a record address field separate from the data in a record. All modern disk drives have sector address fields, called ID fields, separate from the data in a sector. Also in 1961 Bryant with its 4000 series introduced

4488-451: Was only manufactured until Commodore got its production lines going with the 1571 , the double-sided drive. Finally, the small, external-power-supply-based, MFM-based Commodore 1581 3½-inch 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 adds more than one drive to a system, the user has to cut a trace in

4556-577: Was quickly corrected. Later versions of the 1581 drive have a smaller, more streamlined-looking external power supply provided with them. 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 BAM Contents, 40/1 BAM Contents, 40/2 Commodore 1541 The Commodore 1541 (also known as

4624-427: Was the case with early hard drives and most floppy disks, the sectors towards the outside of the disk are physically longer than those nearer the spindle. Because each sector still contains the same number of bytes, the outer sectors have lower bit density than the inner ones, which is an inefficient use of the magnetic surface. The solution is zone bit recording, wherein the disk is divided into zones, each encompassing

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