# Tristate Buffer Output if Input is High-Z?

Teo Zenios teoz at neo.rr.com
Thu Sep 29 16:16:42 CDT 2005

```All the IIfx ram I have and have seen were 9 chip (1MB and 4MB SIMMs). I
think the 16MB SIMMs were very tall and had more then 9 chips on them like
the ones in the picture below.

http://www.mathdittos2.com/columns/bh/bh990511.html

The machine pictured has 68MB of ram (4x16MB plus 4x1MB). 128MB is the
maximum ram available. It looks like the 16MB SIMMs in the picture have 36
chips on them (probably the same chips that make up the 4MB part just 4
times as many).

I Hope this helps.

----- Original Message -----
From: "Eric J Korpela" <korpela at ssl.berkeley.edu>
To: "General Discussion: On-Topic Posts Only" <cctech at classiccmp.org>
Sent: Thursday, September 29, 2005 5:01 PM
Subject: Re: Tristate Buffer Output if Input is High-Z?

I also notice that the table on page 2 of the technote contradicts the IIfx
section. The table says you can put up to 128MB in a IIfx, but the IIfx
section says the biggest SIMM allowed is 256kx8.

Eric

On 9/29/05, Eric J Korpela <korpela at ssl.berkeley.edu> wrote:
>
> Anyone have a datasheet for Hitachi HM511000AJP8 DRAMs? It's used in at
> least some IIfx SIMMS.
>
> What's the deal with parity on the IIfx? Is the parity bit stored off the
> SIMM? The technote
http://developer.apple.com/technotes/hw/pdf/hw_25.pdfmentions parity, are
there 9-chip SIMMS on the IIfx? Or is the parity stored
> on a separate RAM on the mainboard? Since your max memory is 8x(4Mx8bit
bit
> SIMMS) accessed 32 bits at a time (I assume) you'd only need 1 Mbit of
> parity RAM if you do parity across 32 bits.)
>
> Eric
>
>
>
>
>
>

```