Apple Macintosh L2 cache SIMM

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01 Mar 1998

Updated: 29 Jun 2026

The Apple Macintosh L2 cache SIMM is a 160-pin proprietary DIMM-style connector used to attach second-level cache modules to selected Power Macintosh logic boards, including the 7200, 7500, 8500, and 9500 models. The socket fitted to the logic board is a Burndy ELF160; physical keying — a 25-35-20 pin grouping on PCI-era models — prevents inadvertent installation of mechanically incompatible modules from other Power Macintosh families. The connector carries both +5 V and +3.3 V power rails alongside a 64-bit data bus (D0–D63), address lines A0–A28, and a set of proprietary cache-control signals. Cache modules were available in capacities of 256 KB, 512 KB, and 1 MB and are electrically and mechanically incompatible with the earlier 120-pin Euro-DIN cache card slot used in the Macintosh IIci.

DIMM = Dual Inline Memory Module DRAM = Dynamic Random Access Memory, Synchronous to Positive Clock Edge

160 pin CONNECTOR

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	+5 V	41	/TOEN	81	+3.3	V 121	/DOEN
2	GND	42	/TWEN	82	GND	122	/DWEN
3	D0	43	/ADV	83	D1	123	/ADSC
4	D2	44	A12	84	D3	124	/CSIZ(2)
5	D4	45	CSIZ(1)	85	D5	125	GND
6	D6	46	A14	86	D7	126	A13
7	GND	47	A16	87	GND	127	A15
8	D8	48	A18	88	D9	128	A17
9	D10	49	A20	89	D11	129	A19
10	D12	50	GND	90	D13	130	GND
11	D14	51	A22	91	D15	131	A21
12	GND	52	A24	92	GND	132	A23
13	+5 V	53	A26	93	+3.3 V	133	A25
14	GND	54	A28	94	GND	134	A27
15	D16	55	GND	95	D17	135	GND
16	D18	56	+5 V	96	D19	136	+3.3 V
17	D20	57	GND	97	D21	137	D33
18	D22	58	D32	98	D23	138	D35
19	GND	59	D34	99	GND	139	D35
20	D24	60	D36	100	D25	140	D37
21	D26	61	D38	101	D27	141	D39
22	D28	62	GND	102	D29	142	GND
23	D30	63	D40	103	D31	143	D41
24	GND	64	D42	104	GND	144	D43
25	+5 V	65	D44	105	+3.3 V	145	D45
26	GND	66	D46	106	GND	146	D47
27	T0	67	GND	107	T1	147	GND
28	T2	68	+5 V	108	T3	148	+3.3 V
29	T4	69	GND	109	T5	149	GND
30	T6	70	D48	110	T7	150	D49
31	GND	71	D50	111	GND	151	D51
32	T8	72	D52	112	T9	152	D53
33	T10	73	D54	113	T11	153	D55
34	T12	74	GND	114	T13	154	GND
35	T14	75	D56	115	T15	155	D57
36	GND	76	D58	116	GND	156	D59
37	+5 V	77	D60	117	+3.3 V	157	D61
38	GND	78	D62	118	GND	158	D63
39	CLK	79	GND	119	CPRES	159	GND
40	GND	80	+5 V	120	A11	160	+3.3 V

Notes

The physical keying differs across Power Macintosh families: PCI-era models (7200, 7300, 7500, 7600, 8500, 8600) use a 25-35-20 pin grouping, whilst NuBus-era Power Macintosh models use a 30-25-25 grouping, and the 6200/4400 series use a 35-25-20 grouping. These key differences mean that modules are not interchangeable between families even though all use the 160-pin Burndy ELF160 socket. The connector is entirely proprietary to Apple and conforms to no JEDEC or other third-party standard.

The Apple Macintosh IIci cache card uses a separate 120-pin Euro-DIN connector derived from the Processor Direct Slot and is electrically and mechanically incompatible with the PowerPC L2 cache SIMM; IIci cache cards must not be inserted into Power Macintosh L2 slots, and vice versa.

Signals

+5 V — 5-volt power supply
+3.3 V — 3.3-volt power supply
GND — ground
D0–D63 — 64-bit bidirectional data bus
A0–A28 — address bus (29 lines)
CLK — synchronous bus clock
CPRES — cache module presence detect
T0–T15 — test signals
CSIZ(1), /CSIZ(2) — cache size configuration signals
/TOEN — test output enable
/TWEN — test write enable
/ADV — address valid / advance
/DOEN — data output enable
/DWEN — data write enable
/ADSC — address strobe / cache select

References

Apple Tech Info Library article 18547 — Power Macintosh 7200, 7500, 8500, 9500: Pinouts (Apple Computer, Inc.)
Guide to the Macintosh Family Hardware, Second Edition — Apple Computer / Addison-Wesley, 1990 (ISBN 0201524058)

Category:Memory Connectors