[Duo2400] Re: Alternate RAM

[Andrew Butitta]

> The PowerBook 2400c computer accommodates one SO (small outline) DIMM for
> RAM expansion. The DIMM can have either 16 or 32 MB of additional RAM.
>

Obviously, this is false.. 64M and 96M modules exist.

> The mechanical characteristics of the RAM expansion DIMM are given in the
> JEDEC speciÞcation for the 144-pin 8-byte DRAM SO DIMM. The PowerBook  2400c
> computer can accommodate an SO DIMM with a height of 1.0, 1.25, or  1.5
> inches. While the JEDEC speciÞcation for the SO DIMM deÞnes a Serial
> Presence Detect (SPD) feature that contains the attributes of the module,
> the Macintosh PowerBook 2400c computer does not support the SPD feature.
> The computer requires the DIMM to contain EDO DRAM devices with access
> times of 60 ns or less.

The card itself must be an SO-DIMM I take it...

> IMPORTANT - Unlike the RAM expansion module for the PowerBook 3400
> computer, the SO DIMM for the PowerBook 2400c computer does not require  an
> address buffer.
>

That's a plus... it can take unbuffered EDO RAM... cheaper, easier to find...

> The PowerBook 2400c computer can accept a DIMM that uses 64-megabit DRAM
> devices. The electrical characteristics of such a DIMM must be the same  as
> those of the corresponding expansion module for the PowerBook 3400
> computer: the DRAM devices must be 4 M by 16-bit devices with 12-by-10
> address multiplexing, and the connections to device address bits 9 and 10
> must be swapped on the DIMM.

It sounds like a modified 4x64 part. 32MB chips... 16-bit bus... 4 devices...
64-bit total.. sounds like a standard part so far..

You're right though, Dan. That part about the address bits being swapped.. I
wonder if that's standard practise or not?


> Type of DRAM device
> 512K by 8; 10 row bits, 9 column bits
> 2M by 8; 12 row bits, 9 column bits
> 1M by 4 or 1M by 16; 10 row bits, 10 column bits
> 2M by 8; 11 row bits, 10 column bits
> 4M by 1 or 4M by 4; 11 row bits, 11 column bits
> 4 M by 16; 12 row bits, 10 column bits
>

These sound like per-chip specifics... useful for manufacturers... but is it
useful for us?

> RAM Banks
> The RAM expansion card can have up to four banks of RAM. Banks can be 4  MB,
> 8 MB, 16 MB, or 32 MB in size.
>

4x32MB= 128MB RAM cards.. in addition to what's on board? 128 looks like the
spec max. on the card itself...

The rest is more chip-level specifics. Pico-farads and millivolts and whatnot.


Perhaps ... 3400 chips on a bare SO-DIMM?

$0.02
-Andrew