It wasn't long ago that just single core CPUs were the norm on home computers. But these days we're seeing ever-increasing core counts for less and less money. But, if we can have lots of cores on just one CPU, what's preventing the powers that be from just putting multiple CPU sockets on the motherboard and letting us have even more cores that way?
Well, as it turns out, we actually did have multi CPU platforms for consumer grade chips for quite a long time. In fact, you can find them going all the way back to the pre-Pentium days when we were all rocking 486 in our desktop rigs. But understandably, these setups were quite rare for home users with one of the big reasons being simply, cost.
Although a good CPU these days isn't exactly cheap, it pales in comparison to many popular CPUs of the late 1980s and early 90s. The 486 for example, cost around $1,000 when it launched. Remember guys, this was a single core processor. Another reason, was that most applications for windows were simply not designed to take advantage of multiple processor cores. I mean, this is still true to a lesser extent today, especially with games. But multi threading for most consumer applications was almost unheard of until the mid 2000s. And if you were doing something at home that would benefit from parallel cores such as video editing, well, you're back to that same problem of having to take out a second mortgage.
But as time went on, silicon prices fell, and we ended up with some multi CPU platforms that became somewhat popular with home users. One, was Athlon MP released in 2001, with the MP standing for Multi Processor. It was AMD his first ever attempt at a dual socket platform. And while it was designed with servers and workstations in mind, it did gain some traction among enthusiasts, and a small handful of systems built around Athlon MP even made their way onto store shelves at local retailers.
Another platform that was more specifically focused on home users was Intel Skulltrail from 2008. Now this dual CPU solution was also derived from a server or workstation oriented product, in this case Intel Xeon nine. But, the motherboards had more features that home users and gamers would want like overclocking, and fewer of the more obscure standards you'd typically see on a server board like, remote management.
Intel builds Skulltrail as the ultimate gaming platform, partly because of the raw power that you could get from two CPUs, and partly because it could support multiple graphics cards in Nvidia SLI without an Nvidia chip set, which at the time was a pretty huge deal.
Unfortunately, the platform is mostly remembered as a failure because it was, you guessed it, extremely expensive. Especially when you factor in the high-end CPUs that were required in order to use it, not to mention that the dual CPUs didn't provide much gaming benefit even though it was kind of marketed towards gamers and enthusiasts.
AMD similar Quad FX suffered a similar fate, as performance simply didn't stack up compared to the high costs and demanding power requirements. These days most folks running dual CPU setups at home are using repurposed workstation or server boards. But, despite the greater prevalence of multi threaded programs, these enthusiasts still remain a tiny minority of users.
You see, unlike earlier high-end platforms, where you could only get four or eight cores maximum in a single socket, shrinking transistor sizes and greater power efficiency mean that we can now have as many as 64 cores on a single CPU package, like what we've seen with AMD latest, Threadripper processors. And especially when you factor in simultaneous multi threading, which allows one core to work on two or more threads at the same time, that many cores is enough performance for just about any home user. Even if you're doing something insanely demanding, then you've got the fact that there are potentially latency issues with having two physical processors on the same board that you don't deal with in a single socket system. That means that multi threaded workloads, even if they are well-designed won't necessarily scale perfectly when you add more physical CPUs.
So the short answer to the question we asked at the beginning of the episode, can simply be summed up as, diminishing returns. In much the same way that adding a 13th subwoofer to your car couldn't possibly make your neighbors any more upset than they already are, adding a second or third or fourth CPU to your motherboard is probably not going to make much difference to the workloads you actually care about.