Disk II: Difference between revisions
Fix infobox template name |
Rewrite against Apple's own Disk II manual (now hosted here) and Weyhrich's Apple II History: corrected release to July 1978 and price to $495 pre-order / $595 retail; corrected the mechanism origin (Shugart SA390 supplied without read/write electronics, head load solenoid, track zero or index sensors - not a modified SA400); corrected chip count (about 40 down to 9, then 8 - not one-tenth); deleted unsourced approximations (dimensions, weight, ~15 KB/s transfer rate, 1985 discontinuation, 14... |
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{{Infobox computer peripheral | {{Infobox computer peripheral | ||
| image = | | image = [[File:Disk II.jpg]] | ||
| caption = Disk II Floppy Disk Subsystem ( | | caption = Disk II Floppy Disk Subsystem (model A2M0003) | ||
| manufacturer = Apple Computer, Inc. | | manufacturer = Apple Computer, Inc. | ||
| type = Floppy disk drive | | type = Floppy disk drive | ||
| released = | | released = July 1978 | ||
| price = US$495 pre-order / US$595 retail, including the controller card | |||
| price = US$595 | | interface = 20-pin ribbon cable to a dedicated controller card | ||
| interface = 20-pin ribbon to controller card | | compatible = [[Apple II]], Apple II Plus, Apple IIe | ||
| compatible = Apple II, Apple II Plus, Apple IIe | | media = 5.25-inch single-sided, 35 tracks | ||
| | |||
| model = A2M0003 | | model = A2M0003 | ||
}} | }} | ||
The '''Disk II Floppy Disk Subsystem''' (often | The '''Disk II Floppy Disk Subsystem''' (often written '''Disk ][''', model A2M0003) is the 5.25-inch floppy drive designed for the [[Apple II]] by Steve Wozniak, with the controller card that made it remarkable. It became available in '''July 1978''' alongside the first full release of Apple DOS, at an introductory price of '''US$495''' including the controller for customers who ordered before Apple had stock, and '''US$595''' thereafter.<ref name="a2history">Steven Weyhrich, ''Apple II History'', chapter 5, "The Disk II", apple2history.org. Cited for: availability in July 1978 with DOS 3.1; the introductory price of $495 including the controller card for pre-orders and $595 otherwise; the formatted capacity of 113 K, 23 K more than Shugart's own figure for the SA400; the origin of the mechanism as the stripped-down Shugart '''SA390''' supplied without read/write electronics, head load solenoid, track zero sensor or index hole sensor; the reduction of the controller from about forty chips on S-100 designs to nine and finally eight; the progression from FM at nine and then ten sectors per track to GCR at thirteen; early production of about thirty drives a day by two people; and the later move to Alps Electric mechanisms within a couple of years of introduction to reduce cost. A well-sourced secondary history, cited here as a secondary source; its own footnotes reference ''Byte'' (January 1985), Freiberger and Swaine, and Rose's ''West of Eden''.</ref> | ||
== | == Origin == | ||
By late 1977 the Apple II stored programs on cassette, and did it badly. Mike Markkula put "floppy disk" at the top of Apple's goals at the December 1977 executive meeting after finding that his checkbook program took two minutes to load from tape and another two for its data.<ref name="a2history" /> | |||
Wozniak studied IBM and North Star | Wozniak studied how IBM and North Star controlled drives and concluded that most of the hardware was unnecessary if the data were written differently. Steve Jobs went to Shugart Associates and asked not for a drive but for a '''mechanism''': no read/write electronics, no head load solenoid, no track zero sensor and no index hole sensor. Shugart called these stripped-down units the '''SA390'''. Apple's Cliff Huston made the analogue electronics work reliably and devised the production-line adjustment procedures; the first drive off the line was given to him.<ref name="a2history" /> | ||
== | The result was a controller of '''nine chips''', later '''eight''' when two 555 timers were replaced by a single 556 — against roughly forty on the S-100 controllers of the day.<ref name="a2history" /> Wozniak's encoding work took the format from FM at nine sectors per track, to FM at ten, and finally to group coded recording at thirteen, which is where the '''113 K''' formatted capacity comes from — 23 K more than Shugart got out of the same media.<ref name="a2history" /> | ||
Early production was two people building about thirty drives a day.<ref name="a2history" /> | |||
=== | == Format and capacity == | ||
= | <templatestyles src="Template:StyledTable/styles.css" /> | ||
{| class="wikitable styled-table" style="width:100%;" | |||
{| class="wikitable" | |||
|- | |- | ||
! DOS | ! DOS version !! Sectors per track !! Capacity !! Encoding | ||
|- | |- | ||
| DOS 3.2.1 | | DOS 3.1 / 3.2 / 3.2.1 || 13 || 113.75 KiB (116,480 bytes) || GCR, 5-and-3 | ||
|- | |- | ||
| DOS 3.3 || 16 || 140 | | DOS 3.3 || 16 || 140 KiB (143,360 bytes) || GCR, 6-and-2 | ||
|- | |- | ||
| ProDOS || 16 || 140 | | ProDOS || 16 || 140 KiB || GCR, 6-and-2 | ||
|} | |} | ||
35 tracks, single-sided, 256 bytes per sector. Apple's own manual describes the 13-sector format as holding "over 116,000 characters".<ref name="manual">''Disk II Floppy Disk Subsystem — Installation and Operating Manual'', Apple Computer, Inc., copyright 1978, including Disk II Application Note part number 030-0011-00 dated 30 July 1978 — hosted on this wiki as [[:File:Apple Disk II Floppy Disk Subsystem Installation and Operating Manual.pdf]]. Cited for: capacity of over 116,000 characters per diskette; the controller's two drive connectors (upper pins marked DRIVE 1, lower pins for the second drive); the warning that incorrectly attaching the ribbon cable to the controller can cause considerable physical damage to the drive and its electronics, with the rule that the cable must leave the connector on the side away from the controller card and that every pin must enter its matching hole; the recommendation to fit the cable to the controller card before installing the card in the machine; and the note that the COPY program only works when the two drives' speeds are matched to about one half of one per cent.</ref> | |||
The 16-sector upgrade changed the controller card's firmware; the drive itself was unaltered. | |||
'''Flippy disks.''' Cutting a second write-enable notch in the jacket lets the disk be turned over and used on its other side in a single-sided drive. Commercial software was sometimes shipped this way. | |||
== The connector warning == | |||
= | {{Warning|'''An incorrectly fitted ribbon cable will destroy the drive.''' Apple's own application note is explicit: "If the cable from the disk drive to the controller card is not plugged into the controller's printed circuit card correctly, considerable physical damage can be done to the disk drive unit and its electronics," and in capitals, "YOU CAN PERMANENTLY DAMAGE THE DISK DRIVE IF YOU ATTACH THE CABLE INCORRECTLY."<ref name="manual" />}} | ||
Apple | Apple's two rules:<ref name="manual" /> | ||
# '''The cable leaves the connector on the side away from the card.''' If you have to jam the cable between the connector and the controller board, it is on the wrong way round. | |||
# '''Every pin must go into its matching hole.''' The failure is offsetting the connector by one row or one column, which puts supply rails on signal pins. | |||
Apple's own recommendation is to '''plug the cable into the controller card before putting the card in the machine''', where you can see the pins engage.<ref name="manual" /> | |||
= | The upper set of pins on the controller is marked DRIVE 1; the second drive goes on the lower set.<ref name="manual" /> Each controller therefore handles two drives, and the Apple II's expansion slots allow more than one controller. Later Apple 5.25-inch drives moved to an external DB-19 port, which cannot be misaligned in this way. | ||
== Maintenance == | |||
== | === Head cleaning === | ||
The | The Disk II has a single head, on the lower side of the mechanism. Head contamination shows as read errors that worsen over time, and the usual cause is a perished diskette shedding oxide. Use a 5.25-inch cleaning diskette rather than a swab; cleaning diskettes are mildly abrasive, so use them when there is a reason to and not on a schedule. The general discussion — including what to do about heavy oxide contamination, and why manufacturers of the period told service engineers not to clean heads by hand — is at [[Floppy Drive Repair]]. | ||
=== Speed === | |||
= | Spindle speed drift is a common cause of a Disk II that reads its own disks but not other people's. Apple's own application note gives a sense of how tight the tolerance is in practice: the DOS '''COPY''' program only works if the two drives' speeds are matched "to something like one-half of one percent", and Apple noted there was no easy cure if a customer's drives were not that close.<ref name="manual" /> | ||
Apple | Speed is checked in software — the Apple II utilities of the period (Copy II Plus, Locksmith and similar) include drive-speed tests — and trimmed on the drive's analogue card. Adjust by measurement, not by ear. | ||
== | === Belt and mechanism === | ||
* The drive belt perishes and stretches; a slipping belt gives intermittent faults that look like speed drift. | |||
* | * Clean hardened lubricant off the head carriage rails and re-lubricate with a silicone grease. See [[Floppy Drive Repair]] for what not to use. | ||
* | * The door and cone mechanism should clamp the disk centrally and release cleanly. | ||
* | |||
=== | === Common faults === | ||
{| class="wikitable styled-table" style="width:100%;" | |||
|- | |||
{| class="wikitable" | ! Symptom !! Likely cause !! Action | ||
|- | |- | ||
| Will not read any disk || Fouled head; perished belt; rail drag || Clean, re-belt, re-lubricate before suspecting electronics | |||
|- | |- | ||
| | | Reads its own disks only || Speed drift, or head alignment || Check and correct speed first; alignment needs a certified diskette and a scope | ||
|- | |- | ||
| | | Intermittent, worse when warm || Belt, or a dry joint on the analogue card || Re-belt; reflow suspect joints | ||
|- | |- | ||
| | | Damages disks as soon as they spin || Analogue card damaged by a misfitted controller cable || Stop using the drive immediately and repair the card before inserting anything you care about | ||
|- | |- | ||
| No | | No spindle rotation || Motor, motor drive circuitry, or the controller || Confirm the controller works with a known-good drive first | ||
|} | |} | ||
== | == Successors == | ||
Apple's later 5.25-inch drives — the Disk III for the Apple III, the dual-drive DuoDisk, the half-height drive for the Apple IIc, the UniDisk 5.25 and the platinum Apple 5.25 Drive — all use the same low-level disk format as the Disk II, which is why disks written on one read on the others. They differ in case, height and, from the DuoDisk onwards, in using the external DB-19 connector rather than the internal 20-way ribbon. A full model-number and date table is not given here because this wiki has no primary Apple source for one. | |||
A black-painted Disk II was made to match the Bell & Howell version of the Apple II Plus sold into education. | |||
=== | == Related pages == | ||
* [[Apple II]] | * [[Apple II]] | ||
* [[ | * [[Floppy Drive Repair]] | ||
* [[Recommended Tools]] | |||
* [[ | |||
== References == | == References == | ||
<references /> | |||
[[Category:Apple Vintage Accessories]] | |||
[[Category:Storage Devices]] | |||
{{Navbox-AppleVintageAccessories}} | {{Navbox-AppleVintageAccessories}} | ||
Latest revision as of 02:21, 23 September 2026
| Disk II | |
|---|---|
 |
|
| Disk II Floppy Disk Subsystem (model A2M0003) | |
| Manufacturer | Apple Computer, Inc. |
| Type | Floppy disk drive |
| Price | US$495 pre-order / US$595 retail, including the controller card |
| Interface | 20-pin ribbon cable to a dedicated controller card |
| Compatible | Apple II, Apple II Plus, Apple IIe |
| Model | A2M0003 |
| Media | 5.25-inch single-sided, 35 tracks |
The Disk II Floppy Disk Subsystem (often written Disk ][, model A2M0003) is the 5.25-inch floppy drive designed for the Apple II by Steve Wozniak, with the controller card that made it remarkable. It became available in July 1978 alongside the first full release of Apple DOS, at an introductory price of US$495 including the controller for customers who ordered before Apple had stock, and US$595 thereafter.[1]
Origin
[edit | edit source]By late 1977 the Apple II stored programs on cassette, and did it badly. Mike Markkula put "floppy disk" at the top of Apple's goals at the December 1977 executive meeting after finding that his checkbook program took two minutes to load from tape and another two for its data.[1]
Wozniak studied how IBM and North Star controlled drives and concluded that most of the hardware was unnecessary if the data were written differently. Steve Jobs went to Shugart Associates and asked not for a drive but for a mechanism: no read/write electronics, no head load solenoid, no track zero sensor and no index hole sensor. Shugart called these stripped-down units the SA390. Apple's Cliff Huston made the analogue electronics work reliably and devised the production-line adjustment procedures; the first drive off the line was given to him.[1]
The result was a controller of nine chips, later eight when two 555 timers were replaced by a single 556 — against roughly forty on the S-100 controllers of the day.[1] Wozniak's encoding work took the format from FM at nine sectors per track, to FM at ten, and finally to group coded recording at thirteen, which is where the 113 K formatted capacity comes from — 23 K more than Shugart got out of the same media.[1]
Early production was two people building about thirty drives a day.[1]
Format and capacity
[edit | edit source]| DOS version | Sectors per track | Capacity | Encoding |
|---|---|---|---|
| DOS 3.1 / 3.2 / 3.2.1 | 13 | 113.75 KiB (116,480 bytes) | GCR, 5-and-3 |
| DOS 3.3 | 16 | 140 KiB (143,360 bytes) | GCR, 6-and-2 |
| ProDOS | 16 | 140 KiB | GCR, 6-and-2 |
35 tracks, single-sided, 256 bytes per sector. Apple's own manual describes the 13-sector format as holding "over 116,000 characters".[2]
The 16-sector upgrade changed the controller card's firmware; the drive itself was unaltered.
Flippy disks. Cutting a second write-enable notch in the jacket lets the disk be turned over and used on its other side in a single-sided drive. Commercial software was sometimes shipped this way.
The connector warning
[edit | edit source] | An incorrectly fitted ribbon cable will destroy the drive. Apple's own application note is explicit: "If the cable from the disk drive to the controller card is not plugged into the controller's printed circuit card correctly, considerable physical damage can be done to the disk drive unit and its electronics," and in capitals, "YOU CAN PERMANENTLY DAMAGE THE DISK DRIVE IF YOU ATTACH THE CABLE INCORRECTLY."[2] |
Apple's two rules:[2]
- The cable leaves the connector on the side away from the card. If you have to jam the cable between the connector and the controller board, it is on the wrong way round.
- Every pin must go into its matching hole. The failure is offsetting the connector by one row or one column, which puts supply rails on signal pins.
Apple's own recommendation is to plug the cable into the controller card before putting the card in the machine, where you can see the pins engage.[2]
The upper set of pins on the controller is marked DRIVE 1; the second drive goes on the lower set.[2] Each controller therefore handles two drives, and the Apple II's expansion slots allow more than one controller. Later Apple 5.25-inch drives moved to an external DB-19 port, which cannot be misaligned in this way.
Maintenance
[edit | edit source]Head cleaning
[edit | edit source]The Disk II has a single head, on the lower side of the mechanism. Head contamination shows as read errors that worsen over time, and the usual cause is a perished diskette shedding oxide. Use a 5.25-inch cleaning diskette rather than a swab; cleaning diskettes are mildly abrasive, so use them when there is a reason to and not on a schedule. The general discussion — including what to do about heavy oxide contamination, and why manufacturers of the period told service engineers not to clean heads by hand — is at Floppy Drive Repair.
Speed
[edit | edit source]Spindle speed drift is a common cause of a Disk II that reads its own disks but not other people's. Apple's own application note gives a sense of how tight the tolerance is in practice: the DOS COPY program only works if the two drives' speeds are matched "to something like one-half of one percent", and Apple noted there was no easy cure if a customer's drives were not that close.[2]
Speed is checked in software — the Apple II utilities of the period (Copy II Plus, Locksmith and similar) include drive-speed tests — and trimmed on the drive's analogue card. Adjust by measurement, not by ear.
Belt and mechanism
[edit | edit source]- The drive belt perishes and stretches; a slipping belt gives intermittent faults that look like speed drift.
- Clean hardened lubricant off the head carriage rails and re-lubricate with a silicone grease. See Floppy Drive Repair for what not to use.
- The door and cone mechanism should clamp the disk centrally and release cleanly.
Common faults
[edit | edit source]| Symptom | Likely cause | Action |
|---|---|---|
| Will not read any disk | Fouled head; perished belt; rail drag | Clean, re-belt, re-lubricate before suspecting electronics |
| Reads its own disks only | Speed drift, or head alignment | Check and correct speed first; alignment needs a certified diskette and a scope |
| Intermittent, worse when warm | Belt, or a dry joint on the analogue card | Re-belt; reflow suspect joints |
| Damages disks as soon as they spin | Analogue card damaged by a misfitted controller cable | Stop using the drive immediately and repair the card before inserting anything you care about |
| No spindle rotation | Motor, motor drive circuitry, or the controller | Confirm the controller works with a known-good drive first |
Successors
[edit | edit source]Apple's later 5.25-inch drives — the Disk III for the Apple III, the dual-drive DuoDisk, the half-height drive for the Apple IIc, the UniDisk 5.25 and the platinum Apple 5.25 Drive — all use the same low-level disk format as the Disk II, which is why disks written on one read on the others. They differ in case, height and, from the DuoDisk onwards, in using the external DB-19 connector rather than the internal 20-way ribbon. A full model-number and date table is not given here because this wiki has no primary Apple source for one.
A black-painted Disk II was made to match the Bell & Howell version of the Apple II Plus sold into education.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Steven Weyhrich, Apple II History, chapter 5, "The Disk II", apple2history.org. Cited for: availability in July 1978 with DOS 3.1; the introductory price of $495 including the controller card for pre-orders and $595 otherwise; the formatted capacity of 113 K, 23 K more than Shugart's own figure for the SA400; the origin of the mechanism as the stripped-down Shugart SA390 supplied without read/write electronics, head load solenoid, track zero sensor or index hole sensor; the reduction of the controller from about forty chips on S-100 designs to nine and finally eight; the progression from FM at nine and then ten sectors per track to GCR at thirteen; early production of about thirty drives a day by two people; and the later move to Alps Electric mechanisms within a couple of years of introduction to reduce cost. A well-sourced secondary history, cited here as a secondary source; its own footnotes reference Byte (January 1985), Freiberger and Swaine, and Rose's West of Eden.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Disk II Floppy Disk Subsystem — Installation and Operating Manual, Apple Computer, Inc., copyright 1978, including Disk II Application Note part number 030-0011-00 dated 30 July 1978 — hosted on this wiki as File:Apple Disk II Floppy Disk Subsystem Installation and Operating Manual.pdf. Cited for: capacity of over 116,000 characters per diskette; the controller's two drive connectors (upper pins marked DRIVE 1, lower pins for the second drive); the warning that incorrectly attaching the ribbon cable to the controller can cause considerable physical damage to the drive and its electronics, with the rule that the cable must leave the connector on the side away from the controller card and that every pin must enter its matching hole; the recommendation to fit the cable to the controller card before installing the card in the machine; and the note that the COPY program only works when the two drives' speeds are matched to about one half of one per cent.