IIfx SIMMs; Was: Re: Tristate Buffer Output if Input is High-Z?

[Teo Zenios]

----- Original Message ----- 
From: "Jeff Walther" <trag at io.com>
To: <cctech at classiccmp.org>
Sent: Friday, September 30, 2005 4:41 PM
Subject: IIfx SIMMs; Was: Re: Tristate Buffer Output if Input is High-Z?


> >Date: Thu, 29 Sep 2005 11:55:18 -0700
> >From: Eric J Korpela <korpela at ssl.berkeley.edu>
> >Subject: Re: Tristate Buffer Output if Input is High-Z?
>
> >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.
>
> You are unlikely to ever see a IIfx that actually implements parity.
> It was an option for the IIfx but was very rare in practice.   In
> virtually all cases the IIfx uses an 8 bit 64 pin SIMM with no
> parity.  The presence of parity on the SIMM will not affect
> operation, because on a non-parity IIfx, the SIMM pins for parity
> connections are NC.
>
> A IIfx SIMM built for parity will have 1/8 more capacity.  The extra
> storage for parity is on each individual SIMM.  The pinout for the
> SIMMs is in "The Guide to the Macintosh Family Hardware".  It's one
> of those Addison Wesley books.
>
> I don't have that particular datasheet on hand.  But if you get one,
> I'd like a copy as well.  I imagine it's a pretty standard 1M X 1
> DRAM chip.
>
> >Date: Thu, 29 Sep 2005 14:01:37 -0700
> >From: Eric J Korpela <korpela at ssl.berkeley.edu>
>
> >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.
>
> I think you misread that somehow.  The tech note states that the IIfx
> does not support 256KB SIMMs.  It gives examples of memory
> configurations up to 32 MB, using 4 MB SIMMs, although there's a
> consistent typo in the example where megabit is written instead of
> megabyte.
>
> But the maximum memory capacity is 128 MB, using eight 16 MB SIMMs.
> That was/is the maximum capacity for most of the Mac II family.  The
> exceptions are the original Mac II (68020 based), the Mac IIsi
> (supports 16 MB SIMMs, but only has 4 slots) and the abomination with
> variations known as the IIvi and IIvx.
>
> As far as I know, there can't be 30 pin SIMMs with capacities larger
> than 16 MB, because there are only 12 address pins available and 12 X
> 2 = 24 and 24 address bits yields 16M addresses.  There aren't any NC
> pins left to convert to additional address lines, unless one steals
> the parity pins.
>
> Jeff Walther

The IIfx uses 64 Pin SIMMs not 30's
The machine CAN do 128MB