On Windows, this only happens if the second instance starts with a specific command-line option (the name escapes me at the moment). Otherwise, the existing instance just opens a new window.

Incidentally, it's amazing that Windows still doesn't let you specify a custom location to create the profile directory of a new user.

> So to not be memory bound you need to run an extra 15 times more instructions... without adding any cache misses, just to execute one instruction per cycle (a fraction of the possible). If it's less you are memory bound.

Yes, if you do operations in a lineal access pattern like this the performance will be bound by the bandwidth. This is the situation I was referring to above.

> Now imagine it's not perfectly sequential, and instead you have to retrieve something from memory before you know where to go next. Like say a database index, binary tree, or linked list. Instead of getting 8 bytes @ 2400 Mhz you get 8 bytes per 70 ns. Keep in mind that's 8 bytes per 1/2.4 ns vs 70 or 168 times worse.

> Suddenly instead of needing 15 times more instructions you need 2500 instructions per memory load, all without a extra cache miss.

> So as you can see it can be quite easy to be memory limited.

No, in this case you will not be limited by the bandwidth, but by the latency. Having more bandwidth will do nothing, because at 8 bytes per 70 ns you're only moving about 109 MiB/s. If 100% of the memory accesses are cache misses (they won't be) and the application uses all cores then yes, doubling the number of memory channels will double the multi-thread performance (unless channel count = core count), although the single-threaded performance will stay unchanged. Additionally, in this particular load you could get away with relatively low frequency RAM, which won't significantly affect the latency but will lower the total bandwidth (it will still be way higher than 109 MiB/s) and will be cheaper.

I can't speak for the server market, but I'm certain that the high-end desktop market is composed primarily of people who do run top-of-the-line specs just for fun.

Generally speaking, databases are kept in memory to minimize latency, not maximize throughput. Bandwidth is not really a problem. Having to update 10 GB/s of a database would be highly unusual. Having to get data from random positions in a disk or SSD is much more common.

As for the message broken, it's not clear to me why the bandwidth would "of course" be the limiting factor.

Sure, that's the theory, but in practice it doesn't seem to make much of a difference, at least not for dual vs. single.

Going from single channel to dual channel offers like an 8% performance increase, IIRC. Is there any reason to expect any different with quad channel RAM?

Wait, was that actually part of a curriculum? Surely if you know what "fiction" and "non-" mean you can understand the difference between the two.