32 bit, 64 bit?

[Arclight]

The following processors implement the Intel 64 architecture:

• Intel NetBurst microarchitecture
  • Intel Xeon (some models since "Nocona")
  • Intel Celeron D (some models since "Prescott")
  • Intel Pentium 4 (some models since "Prescott")
  • Intel Pentium D
  • Intel Pentium Extreme Edition
• Intel Core microarchitecture
  • Intel Xeon (all models since "Woodcrest")
  • Intel Core 2 (Including Mobile processors since "Merom")
  • Intel Pentium Dual Core (E2140, E2160, E2180, E2200, E2220, E5200, E5300, E5400, E6300, E6500, T2310, T2330, T2370, T2390, and T3200)
  • Intel Celeron (Celeron 4x0; Celeron M 5xx)
• Intel Atom microarchitecture
  • Intel Atom 200 series (not to be confused with the N200 series, widely used in netbooks)
  • Intel Atom 300 series
• Intel Nehalem microarchitecture
  • Intel Core i3
  • Intel Core i5
  • Intel Core i7

Yes, from wiki, but reliable afaict.

I agree that when you upgrade, you should stay at the same "performance level". i.e. 3GHz single-core > 3GHz dual-core > 3GHz quad-core. You'll notice some performance improvement from newer architectures, but you shouldn't trade in 1GHz of speed just to get more cores.

The OS can divide the workload over multiple cores, even for applications that are optimized for single-core systems, but this creates overhead for the CPU and thus comes at a performance penalty. (I think, needs some research)