Jump to content

Recommended Posts

I'm going through my stash and I'm coming across more stuff.

 

I bought 4x 64-pin SIMMs from a fellow in Germany who suspected that they were for a IIfx.

The NTX part of the label indicates that these are intended for the LaserWriter IINTX.

I'm guessing that the 70L part at the end of the second line indicates that it is 70ns RAM.

 

I haven't found much online about this particular RAM, or even about the differences between IIfx RAM and IINTX RAM. I seem to remember reading somewhere that IINTX SIMMS can't be used in a IIfx.

 

There is a link to a thread here from the user Tempest who reckoned that they were 4MB SIMMs:

 

On AppleFritter, here's mention of it in a post from 2004: https://www.applefritter.com/node/3712

 

My questions are:

 1. Does anyone have any concrete experience with IIfx & IINTX SIMMs?

 2. Do these SIMMs ring a bell with anyone?

 3. Is it safe for both the SIMMS and my IIfx to try them out?

 

The picture of 2 of them is below:

large.EA7FC40F-DBE9-45FB-8AE1-A6298007FE6F.jpeg.1ffd4392c16801e87fa457586701fab1.jpeg

Link to post
Share on other sites

Hopefully I don't annoy anybody since I can't answer directly to your questions. But I have worked with/on IIfxes in the early 1990s.

I always prefer original sources, which means Apple in this case. Apple's Memory Guide:

https://www.macintoshrepository.org/24780-apple-memory-guide

states (p. 12)

Quote

The Macintosh IIfx uses 64- pin SIMMs similar to those used in the LaserWriter IINTX. Do not use NTX SIMMs in the Macintosh IIfx as they are not the correct speed.

The original Apple leaflet for the IIfx ( http://tech-insider.org/mac/research/acrobat/9003.pdf ) mentions that 80ns SIMMs are needed. In the 1990s I often found that the original memory speeds became difficult to obtain, but faster modules mostly proved to be backward compatible. So this may indicate that your modules, it they prove to be 70ns, may work. What concerns me is that they are copyrighted 1990, quite early, so not sure about the 70ns.

 

However there are no warnings that LaserWriter memory may destroy fx hardware, so it may be worth a try, given the modules look in good shape. But you may encounter the startup crash sound (a minor down chord) and a sad Mac, which does not mean your hardware is toast but the Mac cannot start. However there is always a risk with unknown hardware. So I do not want to make actual recomendations.

 

Remember using always 4 identical modules per bank, and start filling up the fx with the largest modules in bank A (the latter required on many Mac IIs but not specifically mentioned for the fx). Parity memory may also be a concern, but only some specific (rare) models are requiring it, other models may (or may not) just ignore the additional information (same module form factor).

 

 

 

Link to post
Share on other sites
8 hours ago, dan.dem said:

Hopefully I don't annoy anybody since I can't answer directly to your questions. But I have worked with/on IIfxes in the early 1990s.

I always prefer original sources, which means Apple in this case. Apple's Memory Guide:

https://www.macintoshrepository.org/24780-apple-memory-guide

states (p. 12)

The original Apple leaflet for the IIfx ( http://tech-insider.org/mac/research/acrobat/9003.pdf ) mentions that 80ns SIMMs are needed. In the 1990s I often found that the original memory speeds became difficult to obtain, but faster modules mostly proved to be backward compatible. So this may indicate that your modules, it they prove to be 70ns, may work. What concerns me is that they are copyrighted 1990, quite early, so not sure about the 70ns.

 

However there are no warnings that LaserWriter memory may destroy fx hardware, so it may be worth a try, given the modules look in good shape. But you may encounter the startup crash sound (a minor down chord) and a sad Mac, which does not mean your hardware is toast but the Mac cannot start. However there is always a risk with unknown hardware. So I do not want to make actual recomendations.

 

Remember using always 4 identical modules per bank, and start filling up the fx with the largest modules in bank A (the latter required on many Mac IIs but not specifically mentioned for the fx). Parity memory may also be a concern, but only some specific (rare) models are requiring it, other models may (or may not) just ignore the additional information (same module form factor).

This does sound good. I'll give it a go tonight, if I can.

Thanks.

Link to post
Share on other sites
  • 68020

As an incidental side note, I have seen others create 64pin SIMMs for Amiga but clearly say not for Macintosh use.  Does anyone know why exactly?  I can't be too hard to build new memory, at least I wouldn't think so.  I mean it would be nice to have 16mb modules for the IIfx.  If anyone knows more about this, please post. 

Edited by maceffects
Link to post
Share on other sites
8 hours ago, maceffects said:

They even stamped it on the PCB :lol:

Hah - along with 'Keep Retrocomputing Affordable', which I am loving. 

 

Maybe they're just nobly trying to prevent Johnny G et al from buying them all up and re-selling for massive markup. 

Edited by dzog
Link to post
Share on other sites
  • 68020
8 hours ago, dzog said:

Hah - along with 'Keep Retrocomputing Affordable', which I am loving. 

 

Maybe they're just nobly trying to prevent Johnny G et al from buying them all up and re-selling for massive markup. 

I thought maybe it was something along the lines of keeping the parts in the Amiga community.  I did see someone a year or two ago with 16mb modules and I asked him if they will work for Macs and that guy said no as well.  I can't fathom that if the speed and nature of the chips is correct why it wouldn't work. 

Link to post
Share on other sites

The GVP pinouts are completely different so that’s why those SIMMs won’t work in the Mac.

It would have been quite a coincidence if two separate companies build non-standard RAM and have the pinouts match in the end ;)

 

Link to post
Share on other sites
8 hours ago, Bolle said:

It would have been quite a coincidence if two separate companies build non-standard RAM and have the pinouts match in the end ;)

 

Is Mac IIfx and LaserWriter RAM proprietary indeed? Not some sort of relatively uncommon but still standard RAM?

Does anybody have knowledge about this?

 

Early PowerBooks do suffer from this proprietory RAM issue, or more exactly their users were/are suffering. In the late 1990s I payed about 400 US$ for a 48 MB RAM card for my PB5300, and this was considered a bargain. Few month later I was able to aquire 64 MB of FPM for my 6100 for about 80$.

Link to post
Share on other sites
  • 68kMLA Supporter

Doug Brown already covered the PCB design, but IIRC the bottleneck to continued production has been finding available memory packages to install. They can be pulled from more common SIMMs of the period, too.

 

 

Link to post
Share on other sites
  • 68kMLA Supporter

Yup, I have sourced a fair amount of NOS compatible memory chips and have several PCBs and a stencil ready for a few baking sessions.  I don't like the idea of destroying DEC memory modules, so sourcing unused specimens is difficult.

 

I've gotten most of my Mac stuff out of storage, and should have a quite a few of these to offer soon, many thanks to Doug Brown

 

 

Link to post
Share on other sites
  • 68kMLA Supporter
On 6/7/2020 at 6:27 AM, dan.dem said:

Is Mac IIfx and LaserWriter RAM proprietary indeed? Not some sort of relatively uncommon but still standard RAM?

Does anybody have knowledge about this?

The memory chips are standard.  The way they are wired to the SIMMs is proprietary, in the sense that only Apple ever did it that way.   There's a thread where this is discussed at length.   If you follow the linked threads upstream from Joethezombie to Doug's, to the link he provides on page one and two of his six page thread, you'll find that the link doesn't work.  Sigh.  I hope it comes back.

 

Memory chips have separate D and Q pins for Data.  One pin is Data In.  The other pin is Data Out.   On the vast majority of SIMMs in the universe, the D and Q pins are just wired together and treated as a single I/O pin.

 

On the IIfx, Apple wired the D and Q pins of each memory chip to a unique pin on the SIMM.   This is why they can't use a 30 pin SIMM.   There aren't 8 unused pins available.  And I guess they were already using the 64 pin sockets for ROMs, or maybe there's nothing between 30 and 64.  

 

The reason Apple did this, is that on operations that Write to the RAM, the IIfx buffers the Write data in some register/buffer chips on the logic board.  The memory controller retains the address information.   And the CPU is told that the operation is done.    Then the CPU goes on about its business while the memory controller uses the stored data to complete the Write operation on the SIMMs.

 

If another RAM operation comes along before the Write is completed, then the memory controller might have to stall the CPU a bit, but generally, this frees up a lot of clock cycles for the CPU.   

 

The Read from SIMM pins are wired directly to the Data bus of the IIfx, but during a Write operation, the Read pins are all High-Z so they don't interfere.    It's having the Write pins off in their own little culd'e sac that makes things zoom.

 

Memory chips which are wider than 1 bit combine the Data-in (Write) and Data-Out (Read) pins on the chip.  So they cannot easily be used for the IIfx buffered write scheme.

 

However, by adding a bus switch chip between the SIMM pins and the memory chip pins and controlling it with  the Write Enable signal to the SIMM, one can allow the buffered Write to pass onto the SIMM while keeping the Read pins of the SIMM in high-Z.

 

There's a lot more detail in that thread that's not available.    I ran off a batch of 16MB IIfx SIMMs back around 2005 or so.  I built half the standard way with X 1 chips and built the other half with the above scheme using the much more common X4 chips.

 

IIfx_Front.jpg

 

 

IIfx_Rev2_Front.jpg

 

Edited by trag
Link to post
Share on other sites
  • 68kMLA Supporter
8 hours ago, maceffects said:

@trag Those are interesting, it appears that the chips on the second are still available from one of my contacts in China, which is a big surprise.  Not a big fan of their price but you only need 2...  

As mentioned in that thread that is currently missing, sigh, the SIMMs made with X4 chips work reliably four at a time, but not eight at a time.  They'll also work in a 4 & 4 configuration with the "conventional" SIMMS, and actually, there's a config of 6 & 2 that works.   I suspect too few chips is not sinking enough current in one of the address or control lines and causing ringing, but haven't experimented yet.  It's on the list, right after that PEX ROM DIMM...

 

Still trying to figure out where the last fifteen years went.  Of course the eighteen-year-old might have something to do with it.

Edited by trag
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...