LC 575 Memory Limit

[johnklos]

So is a Quadra 840AV with 512MB (128x4).

Really? I've tried 128 meg SIMMs in various Quadras, but I had no idea that the Q840AV actually works with 128 meg SIMMs... Nice!

Is this a machine you have / use?

 

[Franklinstein]

90% of my stuff is in storage because of weight limits during moves, but yeah, the 840AV is one part of my collection. I fitted it with the RAM and a 7200RPM hard drive (the original was a 1st gen 5400RPM Seagate Hawk) and it's screaming fast.

And yeah, my first 6100/60 had a 250MB hard drive, so it's funny to have more RAM than I used to have disk space.

 

[trag]

So is a Quadra 840AV with 512MB (128x4).

Really? I've tried 128 meg SIMMs in various Quadras, but I had no idea that the Q840AV actually works with 128 meg SIMMs... Nice!

Is this a machine you have / use?

The Q840AV does not work with 64MB nor 128MB SIMMs in my tests. It is possible that Franklinstein had some very differently organized SIMM, but that seems farfetched.

My experiments indicated that the Q840AV and the 7100 and 8100 do not recognize column, nor row addresses above 11 wires. So 11 + 11 bits is 22 bits or 4M addresses. A 72 pin SIMM is 4bytes wide, so one gets 16MB or addressable memory per bank in those machines and dual bank SIMMs can be 32 MB.

In my tests, 64 MB SIMMs are seen as 16MB and 128MB are seen as 32 MB in the above mentioned machines.

Now the 6100 will address 12 X 12 memory chips and it uses the same memory controller as the 7100 and 8100, so one might doubt my results. I was puzzled by this, so I traced the upper address line and the RAS lines back from the SIMM sockets in these machine. In the 6100 those lines go directly back to the memory controller (well, through buffers). In the 7100 and 8100 the upper address line and the RAS signals all pass through a CPLD before going to the memory sockets. My guess is that Apple did not build the memory controller with enough RAS lines to control multiple SIMM sockets. So they translate the RAS lines and upper addresses into multiple RAS lines in the CPLD and use that to support multiple SIMM socket banks.

The Q840AV appears to use the same addressing scheme as the x100 family, which is not surprising because they were so close to each other in development.

 

[olePigeon]

My LC 575 currently has 132MBs installed. I know that this particular memory module works with the LC 575.

 

[yuhong]

My guess is that Apple did not build the memory controller with enough RAS lines to control multiple SIMM sockets. So they translate the RAS lines and upper addresses into multiple RAS lines in the CPLD and use that to support multiple SIMM socket banks.

Which means the total memory limit for all three x100 models are the same, right?

Edit: unfortuately not, because the fact that the 7100 have four SIMM sockets means that some RAS lines are wasted, cutting max RAM by half.

Now what about the 6200/6300/5200/5300 Power Macs? If these have the same memory controller as the Quadra 630, these should support up to 256 MB of RAM, right?

 

[Mac128]

I'm really looking for a 128mb module for my Mystic CC

As long as it's not a Power Mystic, otherwise you're back to the 36MB RAM restriction. Apple giveth and Apple taketh away.

 

[System6+Vista]

I can happily report that my Mystic CC has been running 132 mb very happily since I dropped the 128mb stick in a few months ago. That's 128mb stick + 4mb onboard. Actually, since I'm not really taking advantage of the memory, i've considered taking it out because of the ridiculous start-up time to count the memory. The unit powers on, makes its sound, and then the screen shows no sign of life for a very long time while counting, then boots to more memory than I need. I am thinking of trying to put seinfeld episodes into RAM disk, but otherwise I don't understand why I sought so much memory...other than that 4mb sucked.

Actually, might be 136mb (8mb internal) on second thought. I'll check when reunited with the troops.

 

[Bunsen]

the ridiculous start-up time to count the memory

You can turn that off

 

[System6+Vista]

Glorious! How? I'm in System 7.1

 

[beachycove]

I believe this to be restricted to 8.5 or possibly 8.6 and above. Anyway, it's a late system feature. You open the Memory Control Panel while holding down the Option or Control key or some such, and there is the extra option of turning off the startup memory test.