Editing Apple Macintosh IIci Cache Card

{{Infobox computer peripheral
| name = Apple Macintosh IIci Cache Card
| image = [[File:Macintosh IIci Cache Card, revised (Apple Rescue of Denver).jpg|260px|frameless]]
| caption = The revised card (board 820-0351-A) with its plastic bracket
| manufacturer = Apple Computer
| type = Level 2 static RAM cache card
| interface = 120-pin Euro-DIN cache connector
| compatible = [[Macintosh IIci]] only
| power = +5 V only, 1.0 A (5 W) maximum
| model = M0326LL/A, M0326LL/B
| part_number = 661-1602 (original), 661-1619 (revised)
}}
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The '''Apple Macintosh IIci Cache Card''' is a 32 KB static RAM cache that plugs into the cache connector on the [[Macintosh IIci]] logic board. Apple sold it under order numbers M0326LL/A and M0326LL/B,<ref name="til4832">Apple Computer, Tech Info Library article 4832, ''Macintosh IIci: Using Cache Memory Card (5/94)'', created 26 November 1989, updated 23 May 1994, [http://absurdengineering.org/library/MASTER%20Tech%20Info%20Library/Macintosh%20Hardware/Mac%20II,%20IIx,%20IIcx,%20IIci,%20IIsi%20&%20IIfx/Memory%20-%20RAM%20Issues/TIL04832%20-%20Macintosh%20IIci%20-%20Using%20Cache%20Memory%20Card%20(5-94).pdf absurdengineering.org library]. Source for: the 32K size of Apple's card; the diminishing return beyond 32K and the marginal gain from 64K; order numbers M0326LL/A (discontinued) and M0326LL/B.</ref> and from September 1991 it was included with every IIci.<ref name="til6624">Apple Computer, Tech Info Library article 6624, ''Cache Cards for Macintosh IIci'', created 10 January 1991, updated 9 February 1993, [http://absurdengineering.org/library/MASTER%20Tech%20Info%20Library/Macintosh%20Hardware/Mac%20II,%20IIx,%20IIcx,%20IIci,%20IIsi%20&%20IIfx/Memory%20-%20RAM%20Issues/TIL06624%20-%20Cache%20Cards%20for%20Macintosh%20IIci.pdf absurdengineering.org library]. Source for: the DayStar Fast Cache IIci and the Micron (later Xceed) MBXC1 with 128K; the Apple card included with all IIci computers from September 1991.</ref> Apple's hardware guide says a cache card can improve the IIci's performance "by as much as 50 percent, depending on the application and on the pixel size used by the built-in video display".<ref name="gtmfh">Apple Computer, ''Guide to the Macintosh Family Hardware'', 2nd edition, Addison-Wesley, 1990, Chapter 5 "Memory", "RAM cache card in the Macintosh IIci computer", pp. 222-225: the performance figure; tag RAM and data RAM; hit, miss and write cycles; the CACHE signal inhibiting the MDU; burst fills; the $5200 0000-$52FF FFFF test space; the EnableExtCache, DisableExtCache and FlushExtCache traps; the 120-pin Euro-DIN connector; the warning against fitting a PDS card. Hosted here: [[:File:Apple Guide to the Macintosh Family Hardware 2nd Edition 1990.pdf]].</ref>

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''Macintosh IIci Cache Card versions'''
! Version !! Service part !! Serial number prefix !! Apple's note
|-
| Original || 661-1602 || CF || Can cause frequent system crashes; return to Apple
|-
| Revised || 661-1619 || AF || Replacement for the CF cards
|}
The part numbers, prefixes and notes are from Apple's 1994 module identification manual, where both pages are dated October 1991.<ref name="mi">Apple Computer, ''Module Identification'', PN 072-8124, June 1994, Interface Cards, pp. 4.3.1 "Macintosh IIci Cache Card, Apple P/N 661-1602" and 4.3.2 "Macintosh IIci Cache Card, Revised, Apple P/N 661-1619", both rev. Oct 91 (PDF pp. 251-252), and the part-number cross-reference (PDF pp. 30-31). Hosted here: [[:File:Apple Module Identification (PN 072-8124, June 1994).pdf]] (see [[Apple Module Identification Manual (1994)]]).</ref>

== How the card works ==
The card works directly on the 68030's bus signals. Its RAM is split into tag RAM, which holds the main-memory addresses of the data in the cache, and data RAM. When the processor starts a read, the card checks its tag RAM. On a hit it holds the CACHE signal asserted, which stops the IIci's Memory Decode Unit (MDU) from starting the cycle, and supplies the data itself. On a miss it makes the processor retry the read by asserting BERR and HALT, releases CACHE so the MDU can fetch from main memory, and copies the data into its own RAM as it passes. Fills use burst mode: five clocks for the first longword of a four-longword block and two for each of the other three.<ref name="gtmfh" />

The cache is physical: the card cannot see the 68030's memory management unit. The MMU tables mark NuBus slot space and I/O space as non-cacheable, so accesses there bypass the card.<ref name="dn">Apple Computer, ''Macintosh IIci Developer Notes'' (1989), Chapter 4 "The Cache Connector", pp. 29-39: the 120-pin Euro-DIN connector shared with the SE/30 but with a different pinout; the IIci's 25 MHz clock against the SE/30's 16 MHz; no rear-panel cutout; the physical cache and non-cacheable NuBus and I/O space; Table 4-1 cache address space; Table 4-2 cache control traps; the CACHE signal; the BGACK~ pull-up; Tables 4-3 and 4-4, signals and pinout; Table 4-5, power; the 3.0 by 6.1 inch maximum card size with the component side facing the power supply. Hosted here: [[:File:Macintosh IIci Developer Note.pdf]] (see [[Macintosh IIci Developer Note]]).</ref> System software does not assume anything about a card's organisation. It turns the cache on and off and flushes it through the HWPriv trap (A098) with selectors 4 (EnableExtCache), 5 (DisableExtCache) and 6 (FlushExtCache). Test software can reach the card's data RAM at $5200 0000-$527F FFFF and its tag RAM at $5280 0000-$52FF FFFF, in 32-bit mode only.<ref name="dn" />

Apple chose 32 KB because the gain per kilobyte falls off quickly beyond it. Its tests found 64 KB gave only a marginal improvement for double the static RAM cost, and almost nothing above that.<ref name="til4832" />

== Hardware ==
[[File:Macintosh IIci Cache Card original and revised (Apple Module Identification 1994).png|thumb|360px|The original card, 661-1602 (top), and the revised card, 661-1619 (bottom), from Apple's 1994 module identification manual]]
Both versions carry a VLSI controller in the centre, four cache SRAMs along the left edge, three tag SRAMs on the right, and two surface-mount electrolytic capacitors, but the layouts differ.<ref name="mi" /> On the revised card the cache SRAMs are U2A-U5A, with a small IC at U1A. On the revised card in the Apple Rescue of Denver photograph the controller is a VLSI part numbered 344S1032 ("U3B NMC controller", © 1990), the cache SRAMs are Micron MT5C6408DJ-15 (8K × 8, 15 ns), the tag SRAMs are IDT 6116SA20 (2K × 8, 20 ns), and the two electrolytics, C10 and C22, are marked 22 and 25V.<ref name="ard">Apple Rescue of Denver, product listing "Macintosh IIci Cache Card", https://applerescueofdenver.com/products-page/cards-boards-cpu-macintosh/macintosh-iici-cache-card/ (retrieved 2026-10-04). Listing text: "Apple 661-1619, 820-0351-A. 32K Level 2 Cache"; the card may or may not come with the small plastic bracket that sits on it. The chip and capacitor markings are read from the listing's photograph.</ref> Four 8K × 8 chips make the 32 KB.

The SRAM makers varied from card to card. Owners on TinkerDifferent reported cache SRAMs from Micron (MT5C6408DJ-15), Cypress (CY7C185A-25VC) and Performance Semiconductor (P4C164), and tag SRAMs from Cypress (CY7C128A-20VC), Micron (MT5C1608DJ-20) and Performance Semiconductor (P4C116). The cache chips are 28-pin SOJ and the tag chips 24-pin.<ref name="td">TinkerDifferent forum, thread "Mac IIci Success Story", https://tinkerdifferent.com/threads/mac-iici-success-story.1656/ and page 2 (retrieved 2026-10-04). Posts by rikerjoe (11 September 2022: two electrolytics replaced with tantalums, chime but no video with the card fitted; 16 June 2023: SRAM types on a working and a faulty card; Renesas 6116SA20 fitted as a tag SRAM substitute without curing the fault), ClassicHasClass (17-18 September 2022: in a IIci running NetBSD around the clock the cache card was the part that failed most, about every couple of years, recapped or not; running without it is more reliable but noticeably slower) and speakers (16 June to 1 July 2023: SRAM types; two of three Cypress tag SRAMs testing bad on a TL866; card booting but not caching after replacement; Snooper not testing the card while MacTest Pro does; unsoldered tag SRAM pins found and fixed, after which the card passed MacTest Pro).</ref>

== Fitting and compatibility ==
The card fits only the IIci. The cache connector is the same 120-pin Euro-DIN part the [[Macintosh SE/30]] uses for its processor-direct slot, but the pinout is different. Apple warns that an SE/30 card or any PDS card in the IIci's cache connector will not work and may damage both the computer and the card.<ref name="dn" /><ref name="gtmfh" /> The connector supplies +5 V only, and the card may draw no more than 1.0 A (5 W).<ref name="dn" /><ref name="til6972">Apple Computer, Tech Info Library article 6972, ''Macintosh IIci Cache: Specifications'', created 15 March 1991, [http://absurdengineering.org/library/MASTER%20Tech%20Info%20Library/Macintosh%20Hardware/Mac%20II,%20IIx,%20IIcx,%20IIci,%20IIsi%20&%20IIfx/Macintosh%20IIci%20Information/TIL06972%20-%20Macintosh%20IIci%20Cache%20-%20Specifications.pdf absurdengineering.org library]. Interface: Macintosh IIci Cache Card Connector (120-pin Euro-DIN style); power dissipation +5 V, 5 W maximum.</ref> A card for the connector may be at most 3.0 inches high and 6.1 inches long, with its component side facing the power supply.<ref name="dn" />

Apple's own specification for the IIci lists 32K of level 2 cache and "1 cache" slot alongside the three NuBus slots.<ref name="sp197">Apple Computer, ''Macintosh IIci: Technical Specifications'', https://support.apple.com/kb/sp197 (retrieved 2026-10-04). L2 cache 32K; slots: 3 NuBus, 1 cache.</ref> The IIci runs normally with the connector empty.<ref name="td" /> Other cards were made for the same connector, among them the DayStar Fast Cache IIci and the Micron MBXC1 with 128 KB of cache,<ref name="til6624" /> and IIci accelerators such as MicroMac's Carrera 040 also plug in there.<ref name="basal">"Mac IIci", ''Retro Mac Computing'', http://basalgangster.macgui.com/RetroMacComputing/Mac_IIci.html (retrieved 2026-10-04). Apple's 32K level 2 cache card "made a big difference in performance"; the slot later used for a MicroMac Carrera 040 accelerator with a 33 MHz 68040.</ref> Only one card fits at a time.

To reach the connector, remove the IIci's lid as described in the [[Macintosh IIcx/IIci/ Quadra 700 Service Source]].

== Faults ==
{| class="wikitable styled-table" style="width:100%;"
|+'''Macintosh IIci Cache Card faults'''
! Symptom !! Likely cause !! Action
|-
| Frequent system crashes with an early card || Original card with a CF serial prefix || Apple asked for these cards to be returned and replaced them with the revised card, 661-1619 (AF prefix)<ref name="mi" />
|-
| Startup chime but no video and no startup with the card fitted; normal without it || Faulty SRAM or a bad joint || Run the machine without the card to confirm. One owner found two of the three tag SRAMs dead; another fitted a substitute tag chip without curing the fault<ref name="td" />
|-
| Machine boots with the card but runs slightly slower, or a diagnostic reports a cache failure || Card not caching: a dead or badly soldered tag SRAM || MacTest Pro includes a cache test; Snooper does not. In the reported case the fault was unsoldered pins on a replacement tag SRAM<ref name="td" />
|-
| Crashes after long running || Unknown; reported from round-the-clock use || One NetBSD user replaced cards every couple of years, recapped or not, and now runs without one<ref name="td" />
|-
| Electrolyte residue around C10 or C22 || Leaking surface-mount electrolytic capacitors || Replace both; owners have used tantalum parts. See [[Capacitor Failure Symptoms]]<ref name="td" />
|}
Larry Pina wrote in 1991 that the original IIci cache cards "haven't worked out very well", which agrees with Apple's note on the CF-prefix cards.<ref name="pina">Larry Pina, ''Macintosh II Repair and Upgrade Secrets'', Brady Publishing, 1991, "CPU Maintenance - Logic Board Upgrades", p. 113 (PDF p. 133). Hosted here: [[:File:Macintosh II Repair and Upgrade Secrets 1991.pdf]].</ref>

== Related pages ==
* [[Macintosh IIci]]
* [[Macintosh IIci Developer Note]]
* [[Macintosh IIcx/IIci/ Quadra 700 Service Source]]
* [[Apple Module Identification Manual (1994)]]

== References ==
<references />

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