DIMM SDRAM 168 Pin · AllPinouts

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01 Mar 1998

Updated: 29 Jun 2026

168-pin SDRAM DIMM

DIMM: Dual Inline Memory Module
SDRAM: Synchronous Dynamic Random Access Memory, Synchronous to Positive Clock Edge.

The 168-pin DIMM is the standard SDRAM main-memory module of late-1990s and early-2000s PCs (PC66/PC100/PC133). It carries a 64-bit data path (72-bit with ECC) at 3.3 V and runs synchronously to the system clock. A single module fills a Pentium-class 64-bit memory bank, where two 72-pin SIMMs were previously needed. JEDEC standardised the pinout, and the module was succeeded by the 184-pin DDR DIMM.

The 168-pin DIMM have 84 pins per PWB side. The Front Side board pinout contains left side pins 1-42, and right side pins 43-84. The Back Side board pinout has left side pins 85-126, and right side pins 127-168.

PIN CONFIGURATIONS (Front side / back side)

Pin#	Front Side	Pin#	Front Side	Pin#	Back Side	Pin#	Back Side
1	VSS	43	VSS	85	VSS	127	VSS
2	DQ0	44	NC	86	DQ32	128	CKE0
3	DQ1	45	/S2	87	DQ33	129	/S3
4	DQ2	46	DQMB2	88	DQ34	130	DQMB6
5	DQ3	47	DQMB3	89	DQ35	131	DQMB7
6	VCC	48	NC	90	VCC	132	A13
7	DQ4	49	VCC	91	DQ36	133	VCC
8	DQ5	50	NC	92	DQ37	134	NC
9	DQ6	51	NC	93	DQ38	135	NC
10	DQ7	52	CB2	94	DQ39	136	CB6
11	DQ8	53	CB3	95	DQ40	137	CB7
12	VSS	54	VSS	96	VSS	138	VSS
13	DQ9	55	DQ16	97	DQ41	139	DQ48
14	DQ10	56	DQ17	98	DQ42	140	DQ49
15	DQ11	57	DQ18	99	DQ43	141	DQ50
16	DQ12	58	DQ19	100	DQ44	142	DQ51
17	DQ13	59	VCC	101	DQ45	143	VCC
18	VCC	60	DQ20	102	VCC	144	DQ52
19	DQ14	61	NC	103	DQ46	145	NC
20	DQ15	62	NC	104	DQ47	146	NC
21	CB0	63	CKE1	105	CB4	147	NC
22	CB1	64	VSS	106	CB5	148	VSS
23	VSS	65	DQ21	107	VSS	149	DQ53
24	NC	66	DQ22	108	NC	150	DQ54
25	NC	67	DQ23	109	NC	151	DQ55
26	VCC	68	VSS	110	VCC	152	VSS
27	/WE0	69	DQ24	111	/CAS	153	DQ56
28	DQMB0	70	DQ25	112	DQMB4	154	DQ57
29	DQMB1	71	DQ26	113	DQMB5	155	DQ58
30	/S0	72	DQ27	114	/S1	156	DQ59
31	NC	73	VCC	115	/RAS	157	VCC
32	VSS	74	DQ28	116	VSS	158	DQ60
33	A0	75	DQ29	117	A1	159	DQ61
34	A2	76	DQ30	118	A3	160	DQ62
35	A4	77	DQ31	119	A5	161	DQ63
36	A6	78	VSS	120	A7	162	VSS
37	A8	79	CK2	121	A9	163	CK3
38	A10/(AP)	80	NC	122	BA0	164	NC
39	BA1	81	WP	123	A11	165	SA0
40	VCC	82	SDA	124	VCC	166	SA1
41	VCC	83	SCL	125	CK1	167	SA2
42	CK0	84	VCC	126	A12	168	VCC

Notes

Keying. Two notches in the contact edge encode the module type and voltage: one between pins 10 and 11 marks an unbuffered module, and one centred between pins 40 and 41 marks 3.3 V signalling. A registered/buffered module has its type notch in a different position, so it cannot be fitted in an unbuffered socket. Contact pitch is 1.27 mm (0.05 in).
Serial Presence Detect. A small I²C EEPROM (read on SDA/SCL, addressed by SA0–SA2, write-protected by WP) holds the module’s organisation and timing so the BIOS can configure it automatically.
ECC. The eight check-bit lines CB0–CB7 carry error-correction bits on 72-bit modules; they are not connected on plain 64-bit modules.
Width. One 168-pin DIMM provides a complete 64-bit data path. Unbuffered modules drive the SDRAMs directly; registered modules re-drive command and address through a register and PLL for heavier loading.

Signals

DQ0–DQ63 — bidirectional 64-bit data bus.
CB0–CB7 — ECC check bits (72-bit modules only).
A0–A13, BA0/BA1 — multiplexed row/column address and bank-address inputs (A10/AP doubles as auto-precharge).
/S0–/S3 — chip selects, one per physical row of SDRAMs.
DQMB0–DQMB7 — byte data masks.
/RAS, /CAS, /WE0 — row-address-strobe, column-address-strobe and write-enable command inputs.
CK0–CK3, CKE0/CKE1 — clock inputs and clock enables.
SDA / SCL / SA0–SA2 / WP — serial presence-detect EEPROM data, clock, address and write-protect.
VDD / VSS — +3.3 V supply and ground.

References

Intel PC SDRAM Unbuffered DIMM Specification, Rev 1.0 (1998) — the 168-pin connector pinout, the two-notch keying and the SPD interface.
Micron 168-pin SDRAM UDIMM datasheet (MT8/16LSDTxx64A) — PC100/PC133 unbuffered module, signal set and front/back pin split.

Category:Memory Connectors