A 64-bit architecture is usually a system where addresses (pointers) are 64 bits wide. Sometimes, it can mean a system where the “natural” size for integer computations (the word size) is 64 bits.
The term 64-bit is used for architectures where the address bus and other data units, like the data bus or CPU registers, are 64 bits wide.
64-bit processor architectures include:
- x86-64 x86-64, often known as AMD64, an evolution of 32-bit x86 x86 PC processors by AMD and Intel, found in many server and desktop computers;
- DEC Alpha, a now-discontinued architecture that was popular on workstations in the 1990s;
- ppc64, a 64-bit evolution of the PowerPC/POWER powerpc processor;
- SPARC v9 (Ultrasparc and sparc64), 64-bit evolutions of the Sparc sparc architecture;
- Itanium itanium, also known as IA-64, an architecture by Intel that is not related to IA-32 (which is the name for later generations of x86 processors)
- MIPS64 mips64, a 64-bit version of the MIPS mips architecture;
- ARMv8, an upcoming 64-bit version of the ARM arm architecture
In C and other languages such as C++ and Objective-C with a similar set of machine integer types including int, long and long long, implementations differ as to which types are 32-bit and which types are 64-bit. Windows follows a model called IL32P64: int and long are both 32-bit, long long (if available) and pointers are 64-bit. On the other hand, most Unix-like systems including Linux and Mac OS X follow the I32LP64 model: int is 32-bit, long and long long and pointers are 64-bit.
