> There was a whole cottage industry of folks modding these CPUs as a small side hustle for people who were not comfortable with soldering onto CPU pins if you wanted to put these into a SMP system.

When Intel switched from Slot 1 to Socket 370, there was a market for "slocket" adapters that allowed Slot 1 motherboards to take Socket 370 CPUs. The best of these adapters worked out a way to re-enable SMP on Celerons by tweaking the pin layout to disable the lock Intel had added. What made the BP6 so popular is that it was a native dual-slot Socket 370 motherboard that had this modification built in so it could use unmodified dual Celerons out of the box.

> Performance really did mostly scale linearly with clock speed back then - but for a single CPU. The dual CPU setups were not nearly as efficient due to software not being as multi-threaded as it is today. The big win were folks with two monitors (rare!) who could run apps on their second monitor while playing games on the first. Typically you would only see frame-rate increases with CPU clock - and of course the very start of the serious 3D accelerator (3dfx, nvidia, ATI) scene back then.

Even if you only had one monitor, multitasking was FAR better on a dual-CPU machine than on a single CPU system. For example, if you were extracting a ZIP file, one CPU would get pegged at 100% but the system was still responsive due to the second CPU not having any utilization. If you use a dual-Celeron BP6 system, it's a much nicer and more modern feeling experience than using a single-PII system even with the faster CPU with more cache.