I think probably because the PAL adds delay which the 386 tolerate but the 486 won't.The part number KTA-MAC II/4 seems to further confirm this is a Mac II/IIx 4MB PAL SIMM.
I tried a set of four 4MB PAL 30-pin SIMMs from a Mac II in a couple PCs years and years ago. The 386 PC recognized all 16MB and booted. The 486 PC hung up during the POST. I was puzzled at the time that the newer system didn't like the RAM. I ended up finding some 8 chip 30-pin SIMMs without the PAL chip to discover the Mac didn't like those, but both 386 and 486 did. My expectation is that your mileage may vary trying them in other systems. They are probably somewhat less compatible than other 8 chip 4MB 30 pin SIMMs. They are also probably somewhat more valuable than other 4MB 30-pin SIMMs.
The technote dougg3 links to states: "Consolation for SIMM manufacturers: SIMMs constructed with an on-board PAL are not necessarily Macintosh II-specific. SIMMs constructed in this manner should work without modification in any usage calling for 4 MB SIMMs (except in the unlikely event that the new test mode is required)."
Post #15 by yuhong
| Source Forum | 68kMLA |
|---|---|
| Category | PowerPC |
| Post Date | Sun, 11 Oct 2015 - 02:38 |
| Original URL | https://68kmla.org/bb/threads/trying-to-identify-some-old-ram.2505/ |
Post
I think probably because the PAL adds delay which the 386 tolerate but the 486 won't.