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SE/30 RAM speed. <120ns ok?
Posted by: Alex on 2018-08-08 03:47:10
The initial question is can I use 120ns or faster RAM on the SE/30?

For example, can I populate RAM on the two banks as follows;

Bank A - 4 SIMMs @ 60ns

Bank B - 4 SIMMs @ 60ns

How about;

Bank A - 4 SIMMs @ 60ns

Bank B - 4 SIMMs @ 120ns

If any of this is allowed are there considerations on which Bank should hold the faster RAM?

In extension to this, are there considerations on which Bank holds the larger sized RAM? 

Any advice would be appreciated. I see a lot of RAM at decent prices but they are all showing up as 60ns RAM, 120ns seems difficult to come by.

Thank you!
Posted by: ArmorAlley on 2018-08-08 04:20:15
The general rule is that faster RAM can be used in place of slower RAM. The specs should properly read 120ns *or faster* RAM is required.

The ideal scenario is 2 banks filled with RAM from the same batch. Then 8 sticks of RAM of the same type and so on down to mixed RAM.

I would expect mixed banks to work just fine, while not being too surprised at the occasional crash. I'm not too surprised by the occasional crash on macs anyway. It wasn't uncommon 30 years' ago.
Posted by: AlpineRaven on 2018-08-08 04:37:59
I was taught "the lower nanoseconds the better" 

Cheers

AP
Posted by: mraroid on 2018-08-08 07:14:54
I was taught "the lower nanoseconds the better" 

Cheers

AP
Hi AP......  I have thought this as well. I have wondered if the board would be able to use the fastest speed installed.  Any limit or how fast?  If the RAM is too fast, with the board just process as fast as it can?

Thank you,

mraroud
Posted by: ArmorAlley on 2018-08-08 08:39:50
The speed at which the RAM is accessed is set by the board. 60ns SIMMs can be read twice as fast as 120ns SIMMs. A board that accesses the RAM at 120ns will access 60ns RAM at 120ns, not at 60ns (unless you do some jiggery-pokery to the relevant crystal on the board). It won't use the RAM at its fastest.

So, 30-pin SIMMs from a Quadra will work in a Mac II but not the other way around.
Posted by: Alex on 2018-08-08 14:25:04
ok I found the answer. It is in the "Macintosh_SE_30_Owners_Guide_1988". I guess I should RTFM.

I wanted to attach the owner's guide but I don't have enough space so I am attaching page 83 of the guide (page 101 of the PDF).



Macintosh SE/30 SIMMs should be rated at 120 nS access time or faster. Installing the slower 150 nS SIMMs available for other models of Macintosh computers is not recommended and may cause loss of data.



SE:30 RAM SIMMs should be rated at 120 nS or faster.png

View attachment Macintosh_SE_30_Owners_Guide_1988 PAGE 101.pdf
Posted by: Unknown_K on 2018-08-08 14:34:00
I never seen 150ns 30 pin SIMMs.
Posted by: Alex on 2018-08-08 14:46:25
I may as well add this general Macintosh memory guide from Apple Service Source.

View attachment memguide.pdf
Posted by: Alex on 2018-08-08 14:49:39
I never seen 150ns 30 pin SIMMs.
Two SE types and the Plus use 150ns. See the Apple memory guide PDF I posted, they are mentioned as 150ns.
Posted by: Unknown_K on 2018-08-08 14:53:23
Never owned a plus and I think the SE's I have seen were 120ns, will have to check (I upgrade them to 4MB with newer RAM anyway).
Posted by: Alex on 2018-08-08 15:38:10
Judging from the "warning" in the screenshot I posted, I think it would be fair to assume that the SE user guide would mention a similar warning on 150 nS or faster RAM.
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