RAM for LC575 & Color Classic Mystic

[JDW]

I posted this question on FaceBook (Vintage Apple Macintosh Enthusiasts group) 5 days ago and not a single person replied, so let's see if the amazingly knowledgable folks here at TinkerDifferent can do better!

Do any of you have experience using any of the following Keystron RAM SIMMs in your LC575 (Mystic) motherboards?

64MB EDO 72pin 60ns:
https://www.ebay.com/itm/161121922148
64MB EDO 72pin 50ns:
https://www.ebay.com/itm/150967645418

I'm trying to gather first-hand experiences which tell me, "yes, I use it and can confirm it works perfectly and fits perfectly in an LC575 motherboard." If you have experience using those exact SIMMs in another LC-series Mac, please report that as well. Surely, there must be at least one person on this planet who has put that RAM in something other than an Amiga!

THANKS, friends!

 

[MacinJosh]

Hi @JDW

It just so happens that I am running a Keystron 128MB in my Mystic CC (and Atari TT030). Works brilliantly for years now.

Do note that boot-up on the CC takes a long time. The CC is doing a memory check while the screen is blank so one would mistakenly assume that the RAM does not work if not waiting long enough. I just timed it. It took 55 seconds from chime to screen waking up.

 

[JDW]

Thank you very much for your reply! I Googled your part number but that 128MB stick appears no longer sold.

The 4 reasons why I am desperately seeking first-hand experiences with the specific RAM linked in my opening post (RAM that is currently sold) is the following:

1. EDO RAM is not 100% the same as FPM RAM. Some old Macs don't like EDO RAM. Seems like your stick is FPM, not EDO, which makes sense why it works fine for you.
2. Some EDO RAM is 3v and others 5v. Macs tend to need 5v. I believe your 128MB stick is 5V, which again explains why it works fine in your Mystic.
3. I linked 64MB modules which should boot faster than 128MB due to their smaller size. 64MB is more than enough RAM anyway, so having 128MB is not necessary for most people in an LC575 motherboard, especially since you have another 4MB of RAM on the motherboard too.
4. When I release my overclocking video, I want to be able to inform people about where to buy FULLY COMPATIBLE RAM for their CC Mystic or LC575 Macs, hence my query about the RAM I linked in my opening post.

 

[This Does Not Compute]

My experience is that the LC 5xx (and Color Classic) need FPM. Interestingly, while the Apple Developer Note for the 575 says that modules need to be 80ns or faster, it doesn't offer much else in terms of specifications beyond mechanical drawings and pin assignments. The 575 service manual doesn't list EDO/FPM either, and confusingly, says that modules need to be 100ns or faster. This guide basically says that all 68k Macs should use FPM, while Power Macs can use EDO. And indeed, searching through this Apple memory upgrade guide from 1998 (PDF), the only entries for "EDO" are for Power Macs. Could you use EDO modules in 68k machines? Maybe, depending on the modules and their design/components used, but since you're looking for ones you can recommend to others to work reliably, I think I'd avoid EDO entirely.

 

[JDW]

...since you're looking for ones you can recommend to others to work reliably, I think I'd avoid EDO entirely.

Recommending FPM RAM is best, I agree, but in terms of newly made RAM that is easy to find and buy at a reasonable price (i.e., not older RAM sold at auction), the Keystron brand is about the only thing I can find. The issue thought is that it is all EDO, not FPM.

Here's a link to all the Keystron RAM currently sold:

64mb ram | eBay

I went through all that and narrowed down the list to the two 64MB modules in my opening post because I didn't think the others would be compatible. But again, even the two 64MB sticks I extracted from all those modules are EDO.

Hmmm...

Then of course we must consider voltage. I must assume the EDO RAM used by @Mr. Fahrenheit is 5V instead of 3V. Not sure about the two 64MB sticks I linked in my opening post.

 

[Kai Robinson]

Just a quick note that EDO is iirc a superset/extension of FPM - and you can make an EDO SIMM work as an FPM by tying /OE to /CAS, iirc - @Zane Kaminski had more information on this, though:

https://tinkerdifferent.com/threads/5v-fpm-dimms.136/post-1190

 

[JDW]

Thank you for the replies!

The still unanswered question about the 2 types of Keystron RAM I linked in my opening post is this:

Are those Keystron 64MB SIMMs 5v or 3v?

If 3v, I assume they won't work in an LC575 MB. Are your working EDO SIMMs 5v, @Mr. Fahrenheit ?

 

[JDW]

@Kay K.M.Mods showed me the photo below in the past, which means he got that particular model number to work fine in his Mystic. That implies the 64MB modules I link in my opening post should also work, but I'm still unclear on the voltage. I doubt that his 128MB module is 5v and the 64MB versions 3v, but I guess I will need to contact the EBAY seller to find out.

Kay also has used the following 64MB SIMMs with success in the past, which are also EDO...

 

[JDW]

So based on the RAM that Kay Koba and Mr. F. have, it would seem that PARITY doesn't matter, and RAM with 7 or 8 or more chips doesn't matter either. Although we've not gotten too specific about what vintage Macs all of this RAM works in, except that Kay's RAM does indeed work in the LC575 motherboard, which I am most concerned about. I must assume that holds true for Mr. F's RAM too, since he mentions it works "in various 040 Macs."

I wrote to Keystron on EBAY yesterday, and here is their reply...

Some of these old Mac PCs requires FPM SIMMs but LC575 will take EDO fine. You have to test each model to find out its compatibility with the EDO SIMMs. If we sell SIMM Kit listed for Apple/Mac, we will always ship SIMMs with FPM chips unless we have tested its compatibility with the listed models. The chips rated at 3V or 5V should not make the difference. EDO or FPM matters. Both voltages should work fine on Mac.
Good luck.

Since the LC575 is primarily what I was concerned about, their reply confirms that either of the 64MB SIMM modules will work fine.

Why 64MB instead of 128MB or 32MB? Because I could not find a 32MB EDO 72-pin SIMM from them on EBAY, and because 128MB is overkill for an LC575 with 040 CPU AND it will increase boot times considerably. I suspect that 64MB would boot in half the time as the 128MB, and of course, 32MB would be faster still. Also keep in mind you have another 4MB of RAM on the motherboard too, which means you have 36MB, 68MB and 132MB respectively (total RAM).

I believe what I will do is provide a link to this thread under my overclocking video to help people who are searching for more RAM find what they need. My humble thanks to all who very kindly contributed!

 

[Stephen]

View attachment 3168

The chips in this photo are 3.3V.

 

[JDW]

The chips in this photo are 3.3V.

Thank you, Stephen! That datasheet covers the 128MB VRAM stick owned by Kay Koba.

Checking the IC p/n on the 64MB VRAM sticks linked in my opening post (as per the photos on EBAY), I see they too are 3.3V!

KM44V16104BK-5 PDF Datasheet - Samsung Semiconductor Division - Datasheets360.com

www.datasheets360.com

So it's rather clear that 3.3V VRAM must work fine in the LC575 MB, as per Kay's use of that Keystron 128MB VRAM stick and based on what Keystron said to me today on EBAY. So I have no idea what vintage Macs require 5V. But since I am focused on the LC575 MB, knowing that 3.3V EDO works is all I need to know.

 

[eric]

Not a lot of markings on this but it's what I'm using in my 575 board currently.

 

[JDW]

View attachment 3203

Not a lot of markings on this but it's what I'm using in my 575 board currently.

How many seconds does it take before you see something on the CRT after pressing the power key on the keyboard?

 

[rikerjoe]

I posted this question on FaceBook (Vintage Apple Macintosh Enthusiasts group) 5 days ago and not a single person replied, so let's see if the amazingly knowledgable folks here at TinkerDifferent can do better!

Do any of you have experience using any of the following Keystron RAM SIMMs in your LC575 (Mystic) motherboards?

64MB EDO 72pin 60ns:
https://www.ebay.com/itm/161121922148
64MB EDO 72pin 50ns:
https://www.ebay.com/itm/150967645418

I'm trying to gather first-hand experiences which tell me, "yes, I use it and can confirm it works perfectly and fits perfectly in an LC575 motherboard." If you have experience using those exact SIMMs in another LC-series Mac, please report that as well. Surely, there must be at least one person on this planet who has put that RAM in something other than an Amiga!

THANKS, friends!

Hi James, this is the 128 MB module I’m using in my Mystic CC that seems to work just fine :

 

[eric]

How many seconds does it take before you see something on the CRT after pressing the power key on the keyboard?

Almost exactly 30 seconds from soft power to hearing the CRT powering up. Another 10 seconds to see the actual picture but the CRT - the OS is half booted already off the BlueSCSI by that point.

 

[JDW]

For those of you with more than 32MB of RAM in your Color Classic Mystic (e.g., a 64MB SIMM or 128MB SIMM), what things are you doing with your Mac to take advantage of all that RAM, or is it largely wasted?

I ask because I have 32MB + 4MB right now, and I am not coming close to filling the RAM. So basically, was your purchase of the 64MB or 128MB SIMM one of convenience? Meaning, you could find a 64 or 128 but not a 32?

 

[eric]

Absolutely nothing In fact I almost always run in 24bit addressing due to using the //e card. The board came with this SIMM.

 

[This Does Not Compute]

I definitely agree with the ego aspect. Growing up we had a 575 as the family computer, and only upgraded it to 12MB total. We never had problems due to limited RAM after that, and that's with using the machine for actual productivity (as opposed to the goofing around we generally do with our retro machines LOL). 36MB is a nice "don't have to worry about anything" amount for a 68k system IMO.

 

[nottomhanks]

Hi James, this is the 128 MB module I’m using in my Mystic CC that seems to work just fine : View attachment 3212

Does that SIMM fit behind the screw mount? I have one that works, but it’s difficult to remove because it’s taller.

 

[rikerjoe]

Does that SIMM fit behind the screw mount? I have one that works, but it’s difficult to remove because it’s taller.

My SIMM is too tall to get past the screw mount when it is pre-installed in the 575 board outside the CC. Instead, I do some hand gymnastics to seat the SIMM properly once the 575 board is installed. I didn’t find a low-profile SIMM when I was sourcing them a year ago - perhaps others have a source nowadays?