RetroTechCollection

Apple UniDisk 3.5: Difference between revisions

← Older edit

Josh (talk | contribs)

5 user groups
9,527 edits
undo
VisualWikitext
Fix category to Apple Vintage Accessories
P4 verification: add Apple's own UniDisk illustrated parts list with part numbers, from the hosted Technical Procedures binder
 
(5 intermediate revisions by the same user not shown)
Line 1: Line 1:
{{Infobox computer peripheral
{{Infobox computer peripheral
| image =  
| image = [[File:Apple Unidisk 3.5.jpg]]
| caption = Apple UniDisk 3.5 (Model A2M2053)
| caption = Apple UniDisk 3.5 (model A2M2053)
| manufacturer = Apple Computer, Inc. (Sony mechanism)
| manufacturer = Apple Computer, Inc. (Sony mechanism)
| type = Floppy disk drive
| type = Floppy disk drive
| released = September 1985
| released = September 1985
| discontinued = 1990
| interface = 19-pin D-sub disk port, SmartPort protocol
| price = US$499
| compatible = Apple IIc with the November 1985 firmware or later; Apple IIe and II Plus with a Liron card; Apple IIGS; Apple IIc Plus
| interface = 19-pin D-sub (SmartPort)
| compatible = Apple IIc (ROM upgrade), Apple IIe (Liron card), Apple IIGS
| dimensions = ~200 mm × 175 mm × 50 mm
| weight = ~800 g
| predecessor = [[Disk II]]
| predecessor = [[Disk II]]
| successor = [[Apple 3.5 Drive]]
| model = A2M2053
| model = A2M2053
}}
}}


The '''Apple UniDisk 3.5''' (model A2M2053) was Apple's first 3½-inch floppy drive for the Apple II series, released in September 1985—four months before the equivalent drive was available for the Macintosh. The UniDisk 3.5 was an "intelligent" or "smart" drive containing its own processor, RAM, and firmware, making it incompatible with the Macintosh despite using an identical Sony 800K mechanism.
The '''Apple UniDisk 3.5''' (model A2M2053) was the first 800 KB 3.5-inch drive Apple shipped for the Apple II, released in September 1985 - before the 800 KB drive for the Macintosh.<ref name="a2h9">Steven Weyhrich, ''Apple II History'', Chapter 9, "The Apple IIc Plus", [https://www.apple2history.org/history/ah09/ apple2history.org], sections "The UniDisk 3.5 and Apple 3.5" and "Advances in Apple II disk storage". The September 1985 release; the order of Apple's four 3.5-inch drives (400K Mac drive, 800K UniDisk 3.5, 800K Mac drive, Apple 3.5); the intelligent-drive design with its own 65C02 and buffer memory, and why the 1 MHz 6502 needed it; the variable-speed modification to Sony's design that gains the extra 80K over 720K; the Apple 3.5's removal of the processor and its 2:1 interleave against the UniDisk's 4:1; the statement that the Apple 3.5 worked on the Apple IIGS and the Macintosh but not on the IIe and the original IIc; the IIc Plus disk port supporting three external 3.5-inch drives and two 5.25-inch drives.</ref>


== Background ==
It is an '''intelligent''' drive: it contains its own processor, RAM and firmware, and the host issues high-level commands rather than driving the mechanism directly. That is why it works on a 1 MHz Apple II at all, and it is also why it will not work on a Macintosh despite using the same Sony mechanism.


Apple introduced the 3.5-inch format with the Macintosh in 1984, but the Apple II's 1 MHz 6502 processor was too slow to handle the higher bitrate of 3.5-inch drives using software-driven control. The UniDisk 3.5 solved this by incorporating its own controller within the drive.
== Why it exists ==
A 1 MHz 6502 cannot take raw data off a 3.5-inch drive, de-nibblise it and hand it to the operating system fast enough. Apple's answer was to put the work inside the drive: a small computer buffers the data and talks to the host over a simple protocol.<ref name="a2h9" /> The cost is speed - the extra processing means the UniDisk works best at a '''4:1 interleave''', where the later, dumber [[Apple 3.5 Drive Service Source|Apple 3.5 Drive]] uses 2:1 and is faster.<ref name="a2h9" />


== Design ==
Apple's design also departs from Sony's: the rotation speed varies with the track being accessed, which packs the inner tracks tightly enough to gain '''an extra 80 KB over the 720 KB''' otherwise available - hence 800 KB.<ref name="a2h9" />


=== Smart Drive Architecture ===
== Inside the drive ==
The UniDisk 3.5 contains substantial internal electronics:
The drive's internals have been documented in detail by a community project that uses the UniDisk as a co-processor for an Apple II:<ref name="rigreco">Riccardo Greco, ''UniDisk 3.5 Apple II co-processor in Merlin Assembler'', [https://github.com/rigreco/UniDisk github.com/rigreco/UniDisk]. '''This is a community project, not an Apple publication.''' It documents the UniDisk 3.5 board's devices and their markings (GTE G65SC02P-2 65C02 at 2.0 MHz in PDIP40; Hitachi HM6116LP-2 2 KB 120 ns static RAM in PDIP24; A2M2053-V1.0 / TC5365P-8718 8 KB 250 ns ROM in PDIP28; VLI VF4060-001 / 344-0041-B IWM in PDIP28), the 527 bytes of gate-array I/O locations and 15 bytes of IWM registers in the memory map, the authorship of the firmware (Michael Askins) and the Liron design team, and the rule that a Disk II in a Protocol Converter daisy chain must be the terminal device and stays dormant while a bus resident is addressed.</ref>
* '''CPU:''' 65C02 at 2.0 MHz (GTE G65SC02P-2)
* '''RAM:''' 2 KB static RAM (Hitachi HM6116LP-2)
* '''ROM:''' 8 KB firmware (A2M2053-V1.0)
* '''Controller:''' IWM (Integrated Woz Machine) chip


This architecture allows the drive to handle disk I/O independently, communicating with the Apple II via the SmartPort protocol.
{| class="wikitable"
|-
! Function !! Device
|-
| Processor || 65C02 at 2.0 MHz - GTE '''G65SC02P-2''', PDIP40
|-
| RAM || 2 KB static - Hitachi '''HM6116LP-2''', 120 ns, PDIP24
|-
| ROM || 8 KB firmware - '''A2M2053-V1.0''' / TC5365P-8718, 250 ns, PDIP28
|-
| Disk controller || IWM - VLI '''VF4060-001''' / 344-0041-B, PDIP28
|}


=== Physical Construction ===
The processor's memory map also carries 527 bytes of gate-array I/O locations and 15 bytes of IWM registers.<ref name="rigreco" /> The firmware was written by Michael Askins, who also wrote the software for the Liron controller card.<ref name="rigreco" />
The drive uses Snow White design language:
* Matching case color for Apple IIc
* Daisy-chain pass-through connector
* Manual eject button
* Sony 800K double-sided mechanism


=== SmartPort Interface ===
== SmartPort and the daisy chain ==
The 19-pin D-sub connector uses the SmartPort protocol:
The 19-pin D-sub disk port carries Apple's '''Protocol Converter''' protocol, later renamed '''SmartPort'''. The host sends high-level commands; the drive does the low-level work; and several devices can be chained.<ref name="rigreco" /><ref name="a2h8">Steven Weyhrich, ''Apple II History'', Chapter 8, "The Apple IIc", [https://www.apple2history.org/history/ah08/ apple2history.org]. The UniDisk 3.5 firmware upgrade for the IIc in November 1985, the move from a 16K to a bank-switched 32K ROM, and the resulting support for four 3.5-inch drives, or three 3.5-inch drives and one 5.25-inch drive.</ref>
* Drive handles low-level disk operations
* Host computer issues high-level commands
* Enables use with slower processors
* Supports daisy-chaining multiple devices


== Compatibility ==
'''A Disk II in the chain must be last.''' The Protocol Converter bus is a daisy chain of the disk port, one or more intelligent devices, and optionally one Disk II, which "must be the terminal member of the daisy chain and remains dormant when a bus resident is addressed".<ref name="rigreco" /> A 5.25-inch drive in the middle of the chain will not work, and that is a configuration error rather than a fault.


=== Requires Special Hardware ===
On an [[Apple IIc]] with the November 1985 firmware the port supports four 3.5-inch drives, or three 3.5-inch drives and one 5.25-inch drive.<ref name="a2h8" />
The UniDisk 3.5 cannot use standard Disk II controllers:
 
'''Apple IIc:'''
* Original IIc requires ROM upgrade (256K ROM)
* Later production IIc includes compatible ROM
* IIc Plus natively compatible
 
'''Apple IIe:'''
* Requires Liron controller card (or later SWIM-based card)
* Standard Disk II controller not compatible
 
'''Apple IIGS:'''
* Native SmartPort support
* However, [[Apple 3.5 Drive]] (A9M0106) operates faster
* UniDisk 3.5 was intentionally slowed for Apple II compatibility
 
=== Not Macintosh Compatible ===
Despite using the same Sony mechanism as the Mac 800K drive, the UniDisk 3.5 is ''not'' compatible with any Macintosh. The internal controller circuitry can be bypassed to enable Mac compatibility, but this voids the "smart" functionality.
 
== Format ==


== Compatibility ==
{| class="wikitable"
{| class="wikitable"
|-
|-
! Parameter !! Value
! Host !! What is needed
|-
|-
| Capacity || 800 KB
| [[Apple IIc]] || The '''November 1985 firmware''' (the 32 KB "UniDisk 3.5" ROM) or later. The original 16 KB firmware drives one external 5.25-inch drive and nothing else<ref name="a2h8" />
|-
|-
| Sides || Double-sided
| [[Apple IIe]], [[Apple II Plus]] || A '''Liron''' controller card. A Disk II controller will not do<ref name="rigreco" /><ref name="a2h9" />
|-
|-
| Tracks || 80 per side
| [[Apple IIGS]] || Native SmartPort support<ref name="a2h9" />
|-
|-
| Encoding || GCR variable speed
| [[Apple IIc Plus]] || Native; the external port takes three 3.5-inch drives and two 5.25-inch drives<ref name="a2h9" />
|-
|-
| File system || ProDOS (Apple II), HFS (not recommended)
| Macintosh || '''Not supported.''' The mechanism is the same Sony 800 KB unit, but the Macintosh drives its floppy hardware directly and cannot talk to an intelligent drive<ref name="a2h9" />
|}
|}


The 800K format matches the Macintosh format, enabling disk exchange between platforms when properly formatted.
== Format ==
 
== Specifications ==
 
{| class="wikitable"
{| class="wikitable"
|-
|-
! Parameter !! Value
! Parameter !! Value
|-
| Model number || A2M2053
|-
|-
| Capacity || 800 KB
| Capacity || 800 KB
|-
|-
| Media || 3.5-inch DD floppy
| Sides || Double-sided
|-
|-
| Interface || 19-pin D-sub (SmartPort)
| Tracks || 80 per side
|-
| Internal CPU || 65C02 @ 2.0 MHz
|-
| Internal RAM || 2 KB
|-
| Internal ROM || 8 KB
|-
|-
| Mechanism || Sony 800K double-sided
| Encoding || GCR, with the rotation speed varying by track group
|-
|-
| Case color || Snow White (IIc matching)
| File system || ProDOS on the Apple II; the Macintosh 800 KB format is the same physical format
|-
| Price (1985) || US$499
|}
|}
<ref name="a2h9" />


== Market Reception ==
Disks formatted on a UniDisk 3.5 and on an [[Apple 3.5 Drive Service Source|Apple 3.5 Drive]] are interchangeable, but each is slower reading the other's interleave.<ref name="a2h9" />


The 3.5-inch format was not widely adopted by Apple II users (except IIGS owners):
== The successor: Apple 3.5 Drive ==
* Most commercial software remained on 5.25-inch disks
The '''Apple 3.5 Drive''' (A9M0106), introduced with the [[Apple IIGS]] in September 1986, is the same mechanism with the intelligence removed: no 65C02, no buffering, and the host does the work. That makes it cheaper and, on a machine fast enough to keep up, faster - 2:1 interleave against the UniDisk's 4:1. It '''works on the Apple IIGS and the Macintosh, but not on the Apple IIe or the original Apple IIc'''.<ref name="a2h9" />
* Larger installed base of Disk II drives
* Required expensive controller card for IIe
* ROM upgrade needed for original IIc


The IIGS, with its enhanced capabilities and native SmartPort support, was the primary market for 3.5-inch drives in the Apple II ecosystem.
Apple's published figures for that drive give a sense of what the mechanism itself does:<ref name="a35ss">''Apple 3.5 Drive Service Source'', Apple Computer, Inc. - hosted on this wiki at [[Apple 3.5 Drive Service Source]]. Specifications chapter: 80 tracks per inch and two recording surfaces; track-to-track seek time 6 ms maximum, settle time 30 ms maximum, drive startup time 600 ms maximum; head position accuracy &plusmn;0.035 mm; formatted capacity 800K and unformatted capacity 1,246K; electrical figures for +12 V (10 &micro;A standby, 120 mA typical, 600 mA peak during eject only for a maximum of 2 seconds) and +5 V (10 mA standby, 360 mA typical); operating temperature 5 to 50&nbsp;&deg;C; size 51 &times; 120 &times; 200 mm and weight 1.3 kg. '''These are the Apple 3.5 Drive's figures, not the UniDisk 3.5's.'''</ref>
* Track-to-track seek 6 ms maximum, settle 30 ms maximum, startup 600 ms maximum
* Head position accuracy &plusmn;0.035 mm
* 800 KB formatted, 1,246 KB unformatted
* +12 V at 120 mA typical, rising to 600 mA during eject for up to 2 seconds; +5 V at 360 mA typical
* Operating temperature 5 to 50&nbsp;&deg;C


== Successor: Apple 3.5 Drive ==
Those are the Apple 3.5 Drive's numbers. Apple did not publish an equivalent specification sheet for the UniDisk 3.5, and the UniDisk's own electronics draw more, so do not apply the current figures to it.


The [[Apple 3.5 Drive]] (A9M0106, 1986) replaced the UniDisk 3.5:
== Maintenance ==
* Removed internal controller (cheaper)
* Cross-platform (Mac and Apple II)
* Only compatible with IIGS and IIc Plus
* Faster operation on IIGS


The UniDisk 3.5 remained available for IIe and original IIc users who couldn't use the simpler Apple 3.5 Drive.
=== Heads ===
Clean the heads with a proper 3.5-inch cleaning disk, or with isopropyl alcohol on a lint-free swab with the drive opened and unpowered. Both surfaces have a head; clean both.


== Maintenance ==
=== The eject mechanism ===
 
The commonest mechanical fault on any Sony 800 KB mechanism is the eject and loading gear becoming stiff with old grease. Clean the old grease out completely and regrease with a light plastic-safe grease. See [[Floppy Drive Repair]] for the general procedure.
=== Head Cleaning ===
Use a 3.5-inch head cleaning disk periodically.


=== Firmware ===
=== Firmware ===
The internal ROM can become corrupted or fail. Replacement ROMs are scarce; non-functional smart drives are often converted to "dumb" drives for Mac use.
The 8 KB ROM is a '''mask-programmed A2M2053-V1.0'''.<ref name="rigreco" /> Replacements are scarce. A drive whose intelligence has failed can be converted to a "dumb" drive for Macintosh use, which destroys its value as a UniDisk but keeps a working mechanism in service.
 
=== Common Issues ===


=== Common faults ===
{| class="wikitable"
{| class="wikitable"
|-
|-
! Problem !! Cause !! Solution
! Symptom !! Likely cause !! What to do
|-
|-
| Not recognized || SmartPort not supported || Verify compatible host
| Not recognised at all || Host does not support SmartPort || Check the firmware revision on a IIc, or that a IIe has a Liron card
|-
|-
| Read errors || Dirty heads || Clean heads
| Not recognised in a chain || Wrong chain order || A Disk II must be last in the chain<ref name="rigreco" />
|-
|-
| Intermittent || Failing internal electronics || Difficult repair
| Read errors || Dirty or worn heads, or degraded media || Clean the heads; try a known-good disk
|-
|-
| Slow operation || Normal on Apple II || IIGS operates faster
| Disk will not eject, or grinds || Hardened grease in the eject mechanism || Strip, clean and regrease
|-
| Slow compared with a IIGS with an Apple 3.5 || Normal || 4:1 interleave against 2:1<ref name="a2h9" />
|}
|}


== Collecting ==
== Identification ==
* '''A2M2053''' on the label
* 19-pin D-sub disk connector with a pass-through for daisy-chaining
* Manual eject button
* Case colour matching the [[Apple IIc]] rather than the later platinum


=== Identification ===
An Apple 3.5 Drive (A9M0106) looks similar but has no internal processor; if a drive is being sold as a UniDisk, the model number on the label is the thing to check.
* Model A2M2053 on label
* Snow White case (not Platinum)
* "UniDisk 3.5" nameplate
* 19-pin D-sub connector


=== Value Factors ===
== Apple's own parts list for this drive ==
* Working internal electronics (smart functionality)
* Original packaging
* Condition of mechanism


UniDisk 3.5 drives command higher prices than Apple 3.5 Drives due to their smart drive capability and relative scarcity.
Apple published an '''Illustrated Parts List''' for the UniDisk as Section 4 of its ''UniDisk
Technical Procedures'', which is held here inside the Service Support Training Programs binder
described at [[Service Support Tranning Programs Laserwriter Technical Procedures Jan 1985]].<ref name="lwtp85">Apple Computer, ''Apple LaserWriter Printer Technical Procedures'', preliminary version for internal use only, sections stamped rev. Jan 85 and rev. Feb 85. Held on this wiki inside the Service Support Training Programs binder scan, described at [[Service Support Tranning Programs Laserwriter Technical Procedures Jan 1985]] ([[:File:Service_Support_Tranning_Programs_Laserwriter_Technical_Procedures_Jan_1985.pdf]]).</ref>
Apple's part numbers, as printed:


=== Testing ===
<templatestyles src="Template:StyledTable/styles.css" />
Test on appropriate system:
{| class="wikitable styled-table"
* Apple IIc (with ROM upgrade)
|-
* Apple IIe (with Liron card)
! Part !! Number
* Apple IIGS
|-
| Analog card, UniDisk || '''661-0287'''
|-
| Uni/DuoDisk disk mechanism assembly || '''661-72128'''
|-
| Assembly, cable, LED, D1 || 590-0140
|-
| Assembly, cable, drive to CPU || 590-0327
|-
| Sub-bezel, Uni/DuoDisk || 970-1258
|-
| Shield, bottom || 805-0890
|-
| Shield, top || 805-0891
|-
| Subassembly, bottom cover || 675-5101
|-
| Top case assembly || 675-5103
|-
| Label, drive number, Uni/DuoDisk || 825-0548
|-
| Spring || 870-0023
|-
| Load button || U815-0064
|}


Verify SmartPort functionality, not just basic disk operations.
The same binder carries the '''DuoDisk Analog Card Chip Swapping Chart''', which is component-level
and applies to the closely related DuoDisk analogue card. Apple's warning there is worth carrying
across to this drive as well: inspect the card for melted or broken components before changing
anything, because a card connected to a computer '''with the power on''' typically shows "fuzz" and
an exploded capacitor.<ref name="lwtp85" />


== See Also ==
== See also ==
* [[Disk II]]
* [[Disk II]]
* [[Apple 3.5 Drive]]
* [[Apple 3.5 Drive Service Source]]
* [[Apple IIc]]
* [[Apple IIGS]]
* [[Apple IIGS]]
* [[Apple IIc]]
* [[Floppy Drive Repair]]


== References ==
== References ==
* Wikipedia — Macintosh External Disk Drive
<references />
* wiki.apple2.org — A2 3.5 Drives
* GitHub rigreco/UniDisk — UniDisk co-processor documentation


[[Category:Apple Vintage Accessories]]
[[Category:Apple Vintage Accessories]]


{{Navbox-AppleVintageAccessories}}
{{Navbox-AppleVintageAccessories|state=collapsed}}
Retrieved from "https://wiki.retrotechcollection.com/Apple_UniDisk_3.5"