Ubuntu – Second CPU missing of Dual Core

Core Duo CPU = Intel's line of dual core processors. This means that there are two logical CPU's on a single chip.

Quad Core = Four logical cpu's on a single chip.

Dual CPU = two chips (normally with a single core, but you can do multiple chips of multiple cores as well)

2 CPUs = What it says, two CPU chips

The beauty of multiple processors or multiple cores on a single processor is the ability to perform multiple instructions at the same time in parallel instead of having to wait for one instruction to finish before starting another. This can make it much faster and efficient to perform CPU heavy tasks such as video editing, graphics, gaming, etc. You will only see performance benefits from applications that effectively utilize multithreading, otherwise it will NOT utilitize multiple cores/processors or at the most will rely on any built-in multithreading capabilities of the OS.

Multiple cores/processors can help with multitasking significantly, but you will still have to contend with other potential performance bottlenecks such as the amount of available RAM on your system. If you don't have enough RAM to run all of those processes, it is not going to matter a whole lot how many processors you are banging out instructions on.

http://en.wikipedia.org/wiki/Multi-core_%28computing%29

As mentioned you have a dual-core system, with 2 threads per core.

This is marketed by Intel as hyperthreading and has been done in various ways over the years by various different manufacturers.

To explain it in its simplest form each CPU core consists of a "core" and various architecture around that core that keeps state and process information for each thread. A single threaded core has the architecture to keep 1 thread worth of state information held at a time, a hyperthreaded core keeps two distinct sets of state information, allowing two separate processes to run at once as long as they require different parts of the core (which is reasonably likely to happen as the core consists of multiple units of multiple different types of processing unit).

To simplify how the CPU is seen to the system each hyperthread is seen as a separate CPU, so a dual core, 2 thread per-core processor appears as a quad core processor.

It is also possible for the operating system to use Core-parking (a feature in newer Intel processors) allows the operating system to suspend one half of a hyperthreaded core so that when the extra processing ability of hyperthreading is not needed then the single thread performance is increased as the core is no longer sharing it's cache across 2 threads and can now fully devote the on-core cache to a single thread.