The PC7486SLC-based Amstrad Mega PC Plus upgrade really is running at 33 MHz. Great news: the math coprocessor for the 486SLC has arrived and is recognised perfectly. It is a ULSI Advanced Math Coprocessor SX/SLC rated at 33 MHz, part US83S87. The diagnostic software also identifies it as a ULSI 84x87.

I’ve also been able to run MEMTEST 4.10 across the full 16 MB of RAM I installed, and it passed with no errors. MEMTEST 4.20 does not run though. It simply restarts when I try to boot it from the floppy.

The 16 MB ceiling makes sense, too. The TI486SLC has a 24-bit address bus and can directly address 16 MB of physical memory. No point expecting to squeeze 32 MB out of that CPU!

For now I am still waiting on the replacement RTC module to arrive from Hong Kong. A couple more weeks to go. I’ve also ordered a 4 GB Disk on Module using SLC flash rather than MLC. Hopefully the BIOS will recognise it and I can boot DOS and Windows from it without too much drama. Time will tell! :D

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