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  1. Y

    LC early boards ?

    This also reminds me of the difference between 350mil vs 300mil 4Mbit chips. 
  2. Y

    Recycled Classic — worth persevering with?

    That is not how DRAM generally works. In fact, I think 80ns was the most common DRAM when the Mac Classic was new. And yes it is possible that the 1Mbit DRAM chips on the daughterboard itself may be bad.
  3. Y

    SE/30 and 2 Mb ram sticks

    Notice they have a PAL on them. I wonder what asymmetric DRAM addressing do they exactly use.
  4. Y

    Recommended OS for Macintosh SE

    Actually, the absolute minimum RAM limit for System 7 to boot is 1.5MB.
  5. Y

    Macintosh 512k RAM replacement?

    The reason why it is 200ns BTW was that Apple was one of the early adopters of 256k DRAM back when the chips was expensive. By the time the 256k DRAM chips became more common, it was already mostly replaced by 150ns.
  6. Y

    Picked up two 1984 128k Macs. One working.

    More precisely, it was the early Micron DRAM chips that had problems. Of course, eventually they improved the quality of the chips around the time many other US DRAM manufacturers was forced to shut down after DRAM prices fell in 1985.
  7. Y

    Mac Goodies at Silicon Valley Electronics Flea Market

    Yea, I think the early Micron DRAM chips had a high failure rate.
  8. Y

    Mac Goodies at Silicon Valley Electronics Flea Market

    They also used MT1259 for 256kx1 later on for example.
  9. Y

    MODE32 on SE/30 with 4 Mb RAM

    Yes, try MODE32 7.5 also.
  10. Y

    Quadra dram configuration

    Yes, the chips on 16MB 30-pin SIMMs are supposed to be 16Mx1. To use 4Mx4 chips would require extra logic. These SIMMs was never very popular for several reasons (including early 16Mbit chips being expensive and 400mil). I wonder which kinds of addressing the 512KB/2MB/8MB SIMMs with PALs uses. 
  11. Y

    MODE32 on SE/30 with 4 Mb RAM

    Really?  It is true it sometimes reconfigures the memory controller, but...
  12. Y

    MODE32 on SE/30 with 4 Mb RAM

    They were using MODE32 1.2 which is not supported with System 7.5 and is probably not particularly good even with System 7.1.  I think MODE32 7.5 is overall probably the best solution nowadays.
  13. Y

    The 8MB RAM on PDS slot for Macintosh Portable

    I recommend that you read https://68kmla.org/forums/index.php?/topic/23763-designing-a-portable-ram-card/
  14. Y

    Apple HD20 and SE/30

    Look up the MacIIHD20 INIT.
  15. Y

    Explanation of Macintosh II's memory limit

    On the accelerators, be aware that the original Mac II ROMs don't support the 68030 PMMU and will try to use the HMMU instead, which is bad of course.
  16. Y

    Explanation of Macintosh II's memory limit

    You can check how much RAM the ROM code thinks it have by using "About the Macintosh" without MODE32 loaded. The info should show that most of the extra RAM beyond 8MB is allocated to the system if the ROM code thinks it has more. (Technical details: the applicable lowmem globals are MemTop and...
  17. Y

    Explanation of Macintosh II's memory limit

    That was just an manufacturing error I think.
  18. Y

    Explanation of Macintosh II's memory limit

    The way the memory controller works applies to all of them. 
  19. Y

    Explanation of Macintosh II's memory limit

    (The original Apple technote is pretty misleading on this topic) (This also applies to the Macintosh IIx, Macintosh IIcx, and Macintosh SE/30) The original Macintosh II did not have a PMMU by default. It relied on the memory controller hardware to map the installed memory into a contiguous...
  20. Y

    Macintosh 128k: Mac Plus ROMs

    Only difference is the SCSI code which you won't be using.
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