For an Intel based system keeping the number of cores constant how much difference would there be between two dual core processors and one quad core processor? We run Oracle OLTP databases on two dual core processors. With fewer dual core processors available we may need to switch to quad core, but we are limited to four cores due to licensing issues, so will have to switch to one processor. If we make the switch should I expect to see a change in real world processing speed?
Should be very little difference in performance between two dual core CPUs and a single quad core CPU, if you are using current Intel Xeons.
However, you might expect to see slightly better performance from the quad-core CPU if it is a "true" Quad core design, ala the new AMD Opterons or the new Xeon W5xxx (aka the Core i7 / Nehalem) series.
The Nehalem Xeons' truly astounding leap in performance over prior generations, in a range of applications, speaks for itself. The largest gains came in our scientific computing/HPC tests, where the Xeon W5580 proved to be between 50% and 100% faster than the Harpertown Xeon X5492. We saw a massive performance increase in SPECjbb 2005, as well, along with more modest but still substantial improvements everywhere else.
Check the max memory you can put in each system - it's possible that you may be able to stuff more RAM into a 2xdualcore box than you can into a 1xquadcore box. And more RAM will likely help.
Sorry for the delay spotting this question. There is a huge difference in performance between a dual-processor, dual-core setup and a single-processor, quad-core setup - the latter will be much quicker whichever make and model you go for, the main reason is because everything happens 'on-die' (although there's an argument to be had if you really want to get into it), so latency and overall bandwidth is much better. This is especially true on a true quad-core chip such as the Xeon 55xx-series.