What is the difference between Intel and PPC?

Hardware-wise: PowerPC is a microprocessor developed mainly by the three developing companies Apple, IBM, and Motorola. It is built with reduced instruction-set computer (RISC) which speeds-up the operation of MIPS (million instructions per second). PowerPC is mainly based on IBM’s earlier Power architecture because it has a similar RISC instruction set for microprocessors.

Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. The philosophy behind it is that hardware is always faster than software, therefore one should make a powerful instructionset, which provides programmers with assembly instructions to do a lot with short programs. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instruction

PPC Macs refers to the generation of Macintosh computers created in the mid to late 1990s through to 2006 that used PowerPC RISC based chips made by IBM or Motorola. That last PowerPC based Macintosh, the PowerMac G5 stopped being sold in August 2006. The latest version of Mac OS X a PowerPC chip enabled computer was able to run was Mac OS X 10.5 (Leopard) (so long as the computer supported it).

Intel Macs refers to the newer Macintosh computers (since January 2006) that use Intel's CISC processors. Intel Macs uses EFI instead of BIOS and can run the latest versions of Mac OS X. Intel Macs are also able to run PowerPC compiled applications through a translation layer called Rosetta which is optionally installed in 10.6.

If a program is made available as a Universal binary it is able to run on both PPC and Intel Macs however many new applications released today are Intel only (eg. Google Chrome, Final Cut Studio, Mac OS X Snow Leopard).

When it comes to Apple hardware, the differences between the last generation of PowerPC and the first generation of Intel were fairly minor, as far as the end user experience goes. They used the same form factors, and the all-new internals were quite effectively hidden by the unchanged exterior and the accommodations the operating system made for compatibility.

The last PowerPC Macs were sold in 2006, so any new machine since then is Intel.

In general, Intel Macs can run the vast majority of software created for PowerPC Macs. There is a performance hit for the emulation required, but it runs at acceptable speeds even for complex software like Photoshop. PowerPC Macs cannot run Intel software.

The latest version of OS X, Snow Leopard, is available only for Intel-based Macs.

Intel Macs have access to a feature called Boot Camp, which allows them to boot into Windows at full speed. Intel Macs can also run Windows inside virtual machines with the help of third-party software (VMWare Fusion, VirtualBox or Parallels); there is a minor performance penalty for this, but it's much faster than the emulation required for a PowerPC Mac to run Windows software.