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A term describing a computer architecture based around an ALU, registers and data bus which are 64 bits wide.

64-bit processors were quite common in 1996, e.g. Digital Alpha, versions of Sun SPARC, MIPS, IBM AS/4000. the PowerPC and Intel were expected to move to 64 bits at their next generation - PPC 620 and Intel P7.

A 64-bit address bus allows the processor to address 18 million gigabytes as opposed to the mere 4 gigabytes allowed with 32 bits. There were in 1996 already hard disks which can hold over 4GB. Floating point calculations can also be more accurate.

A 64-bit OS is needed as well to take advantage of the CPU. In 1996 there were only a few 64-bit operating systems, including OS/400, Digital Unix, Solaris (partialy). A 32-bit OS can run on a 64-bit CPU.

64-bit computing

CPUs that process 64 bits as a single unit, compared to 8, 16 or 32. Today's desktop and laptop computers are mostly 64-bit machines; however, there are countless 32-bit, 16-bit and 8-bit microprocessors manufactured every year (see microcontroller).

A 64-bit computer is not twice as fast as its 32-bit predecessor. The 64 bit "word size" is only one aspect of internal processing. The CPU's clock speed, along with the speed of storage, RAM and input/output (the peripheral bus) all play roles in a computer's performance (see throughput). In many cases, the perceived difference between the same brand of a 32-bit and 64-bit computer can be negligible. See word.

More Memory
The major advantage of a 64-bit computer is its larger address bus, which supports considerably more RAM than its 32-bit counterpart. A 32-bit computer is typically limited to 4GB, whereas a 9th-generation 65-bit Intel i9 CPU can handle 128GB and a third-generation 64-bit Mac Pro supports 1.5TB (that's 1.5 terabytes of RAM, not storage).

A Lot of 32-Bit Software
Although CPUs migrated to 64-bits years ago, many 32-bit applications still run in 64-bit computers. The Mac ran 32-bit and 64-bit applications until the Catalina version of macOS in 2019, which supports only 64-bit programs.

Windows comes in both 32-bit and 64-bit versions. The 64-bit version also runs 32-bit apps, and there are many in existence. However, people still run old 16-bit DOS and 16-bit Windows apps that only 32-bit Windows supports. See Intel 64, AMD64, Opteron and Athlon. See 32-bit computing and bit specifications.

References in periodicals archive ?
Animators from YouTube channel 64 Bits took the retro design aesthetics of side-scrolling adventure game 'Cuphead' and gave it a 'Dark Souls' make-over.
Consider partial product 0 (pp0), pp1, pp2 and pp3 are the 64 bits outputs of the 32x32 VM1, VM2, VM3 and VM4 respectively.
* These two 64 bits are added by using RCA2 and produces s2 [64:0].
* These 64 bits are added with 64 bits pp2 by using RCA3 and produces s3 [64:0].
* By using 64 bit RCA1, pp1 and pp2 are added and produces s1 [64:0].
While doing a lot of logical operations on large bit streams, working on 64 bits at a time is a huge advantage.
According to Google, the shift to 64 bits provides a marked improvement in rendering speed, thanks to the latest compiler and processor optimizations and "a calling convention that allows more function parameters to be passed quickly by registers." Google says it sees an average improvement of 25% in graphics and multimedia content.
"We were the first to bring 64 bits and dynamic power management to notebooks, and now the performance of AMD mobile processors is available at your fingertips in a dynamic convertible tablet PC."
While few doubt that the software industry is destined to evolve to 64 bits, evolution is a long, slow process.
With this encoding, default operand size is 32 bits and default address size is 64 bits. Using instruction prefixes, the default operand size can be overridden to 64 bits or 16 bits, and the default address size can be overridden to 32 bits.
"AMD processors including x86-64 technology will permit platform suppliers, developers, corporate MIS departments and consumers to transition to 64 bits gradually, while continuing to run 32-bit applications without incurring performance penalties," the paper says.
In terms of precision, 64 bits is old hat, particularly in engineering programs where rounding errors can be disastrous.