Quadra 700
The System’s Specs, at the Moment
CPU/FPU/MMU: Motorola 68040 (??? Mask) rated 25 MHz @ ~32.5 MHz
Main RAM: ~70 MBytes (?? MBytes + 64 MBytes ???ns, 4×8 MByte “MemoryMasters” brand ???ns SIMMs)
Video RAM: 2.5 MBytes (512 KBytes onboard) + 2 MBytes (8x256KB of 70ns???? VRAM SIMMs from ????)
Power Supply: Original ASTEC supply, RIFA caps have been replaced, original fan
Storage: Internal RP2040?? Mini MicroSD-to-SCSI drive emulator, ???MB Quantum SCSI-1 3.5″ HDD
PDS Slot: 128 KByte Daystar ???cache L2 cache card with 15ns (and one 17ns) SRAM chips
NuBus Slot “1”:
NuBus Slot “2”:
I decided to max out the RAM (and get the fastest I reasonably could), install a drive emulator to remove the most glaring bottleneck of period-accurate Macs, keep the L2 cache card installed and overclock the CPU/CPU bus. I could install a PowerPC 601 card, but decided I’d rather overclock the 68040 and its bus instead, since there are plenty of PowerPC-based systems out there. I also associate the external design of the Q700 with the boxy Mac II series, and that with the 680×0 architecture.
Overclocking, L2 and the Quest for Stability
Curiously, intensive tasks like hundreds of runs of RAMometer and MacTest Pro memory tests, intensive CPU tests like 30+ minutes of running the Doom I attract mode demo, would go without an error or crash. But random crashes would occur during everyday tasks, particularly drag-and-drop operations or “Visual Client” (After Dark) crashing for whatever reason, if the L2 cache card were enabled at 33.33 MHz (66.667 MHz oscillator).
Stability at ~33.33 MHz seemed to improve markedly with the L2 card disabled, so I suspect it’s the cache card that’s the obvious failure point, but more testing (with another 66 MHz oscillator, and 50 MHz for stock) is needed.
The machine seems almost rock-solid at ~32.5 MHz CPU clock (~65 MHz oscillator) with L2 cache card enabled. More testing is required to ensure this, but any crashes since switching oscillators seems software-related, and mostly repeatable.
My next plan is to test other oscillators including another ~66.667 MHz one, to try and identify the failure point(s). I’d like to keep the L2 cache card installed as it does provide a noticeable performance boost, but it may be such that I cannot run it with ~>65 MHz bus clock/32.5 MHz CPU clock.
That said: performance at 25 MHz was plenty snappy, only really slowing me down when I had too many Finder windows open. 8.1 was noticeably slower than 7.x, but perfectly usable. 32.5 MHz runs great, regardless of OS.
(Update 12/2025): Seems VERY stable at 32.5 MHz, with the L2 cache card enabled, still using that 65 MHz socketed oscillator.