30 pin 2MB SIMMs

[Jeff Walther]

>Date: Mon, 29 May 2006 23:58:48 -0300
>From: "Alexandre Souza" <alexandre-listas at e-secure.com.br>


>     Well, there is - believe it or not - 16MB 30-pin SIMM. I always thought
>it was a mistake, but I saw that with my own eyes. Unbeliaveable as it can
>be, there is only ONE equipment I saw using that, which is a Equinox (or
>Ensoniq?) music keyboard. It was the first and last time. I hadn't ever
>stopped to think how can it be possible (maybe a non-standard pinout) but it
>is true indeed, 16 MB SIMMs, four of them making 64MB. Believe it or not.

The 16 MB 30 pin SIMM is not uncommon in the early Macintosh World. 
The Mac II used 30 pin SIMMs and had a theoretical maximum of 128 MB 
of RAM when all eight sockets were populated with 16 MB SIMMs.

I write "theoretical" because I think that there were *details* until 
the SE/30 and IIcx came out around 1989.   The IIx (later than the 
II, but earlier than the SE/30 and IIcx) required PAL SIMMs (not sure 
what these were, except they apparently had a PAL on board) to use 
larger capacity SIMMs.

Anyway, the SE/30, IIcx and IIci all had eight SIMM sockets capable 
of using 16 MB 30 pin SIMMs giving a 128 MB memory capacity back in 
the very late 80s and early 90s.   Quite a forward looking memory 
capacity for the day.  Of course, it was years before you could 
actually get SIMMs with such high capacities.

Later Apple Mac models with the same CPU chips were built with lower 
maximum RAM capacities for no apparent reason other than marketing 
weenies.  Compare, e.g., the SE/30 and the Classic II or Color 
Classic.

The pinout is standard.  There are 12 address lines available on the 
30 pin SIMM, giving a multiplexed address of 24 bits which translates 
to 16M addresses.

Pin 	Name 	Description
1	VCC	+5 VDC
2	/CAS	Column Address Strobe
3	DQ0	Data 0
4	A0	Address 0
5	A1	Address 1
6	DQ1	Data 1
7	A2	Address 2
8	A3	Address 3
9	GND	Ground
10	DQ2	Data 2
11	A4	Address 4
12	A5	Address 5
13	DQ3	Data 3
14	A6	Address 6
15	A7	Address 7
16	DQ4	Data 4
17	A8	Address 8
18	A9	Address 9
19	A10	Address 10
20	DQ5	Data 5
21	/WE	Write Enable
22	GND	Ground
23	DQ6	Data 6
24	A11	Address 11
25	DQ7	Data 7
26	QP	Data Parity Out
27	/RAS	Row Address Strobe
28	/CASP	Something Parity ????
29	DP	Data Parity In
30	VCC	+5 VDC

Sets of four 30 pin 16MB SIMMs typically go for about $25 plus 
shipping on Ebay.

Jeff Walther