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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.
References in periodicals archive ?
While few doubt that the software industry is destined to evolve to 64 bits, evolution is a long, slow process.
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.
According to a report by Giga Information Group (for a study that AMD commissioned, it should be noted), organizations can derive significant cost savings by gradually adding Opteron-based servers as software is transitioned to 64 bits.
Nevertheless, the report also notes a number of intangibles that are likely to affect the success of Opteron, including ongoing future support from Microsoft, buy-in and continuing support from enterprise server vendors, and ISV support, particularly the porting of 32-bit applications to 64 bits.
In terms of precision, 64 bits is old hat, particularly in engineering programs where rounding errors can be disastrous.
AMD Turion 64 mobile technology is the only available processor offering both 64 bits and enhanced security for thin and light notebook PCs, which are preferred by many business professionals," said Marty Seyer, corporate vice president and general manager, Microprocessor Solutions Sector, AMD.
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.
For consumers, 64 bits gives both more memory to load polygons and textures and more power to manipulate them, accessing unprecedented levels of realism, interactivity and detail in their worlds.
To handle speed differences between the VMEbus and PCI bus, and to enable the two buses to operate independently at full speed, OmniVME provides a prefetch FIFO (32 words deep by 64 bits wide) with integrated byte swapping logic.