64-bit computing explained

In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit central processing units (CPU) and arithmetic logic units (ALU) are those that are based on processor registers, address buses, or data buses of that size. A computer that uses such a processor is a 64-bit computer.

From the software perspective, 64-bit computing means the use of machine code with 64-bit virtual memory addresses. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses; x86-64 and AArch64 for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all zeros (000...) or all ones (111...), and several 64-bit instruction sets support fewer than 64 bits of physical memory address.

The term 64-bit also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a word size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them. 64-bit CPUs have been used in supercomputers since the 1970s (Cray-1, 1975) and in reduced instruction set computers (RISC) based workstations and servers since the early 1990s. In 2003, 64-bit CPUs were introduced to the mainstream PC market in the form of x86-64 processors and the PowerPC G5.

A 64-bit register can hold any of 264 (over 18 quintillion or 1.8×1019) different values. The range of integer values that can be stored in 64 bits depends on the integer representation used. With the two most common representations, the range is 0 through 18,446,744,073,709,551,615 (equal to 264 − 1) for representation as an (unsigned) binary number, and −9,223,372,036,854,775,808 (−263) through 9,223,372,036,854,775,807 (263 − 1) for representation as two's complement. Hence, a processor with 64-bit memory addresses can directly access 264 bytes (16 exabytes or EB) of byte-addressable memory.

With no further qualification, a 64-bit computer architecture generally has integer and addressing registers that are 64 bits wide, allowing direct support for 64-bit data types and addresses. However, a CPU might have external data buses or address buses with different sizes from the registers, even larger (the 32-bit Pentium had a 64-bit data bus, for instance).[1]

Architectural implications

Processor registers are typically divided into several groups: integer, floating-point, single instruction, multiple data (SIMD), control, and often special registers for address arithmetic which may have various uses and names such as address, index, or base registers. However, in modern designs, these functions are often performed by more general purpose integer registers. In most processors, only integer or address-registers can be used to address data in memory; the other types of registers cannot. The size of these registers therefore normally limits the amount of directly addressable memory, even if there are registers, such as floating-point registers, that are wider.

Most high performance 32-bit and 64-bit processors (some notable exceptions are older or embedded ARM architecture (ARM) and 32-bit MIPS architecture (MIPS) CPUs) have integrated floating point hardware, which is often, but not always, based on 64-bit units of data. For example, although the x86/x87 architecture has instructions able to load and store 64-bit (and 32-bit) floating-point values in memory, the internal floating-point data and register format is 80 bits wide, while the general-purpose registers are 32 bits wide. In contrast, the 64-bit Alpha family uses a 64-bit floating-point data and register format, and 64-bit integer registers.

History

Many computer instruction sets are designed so that a single integer register can store the memory address to any location in the computer's physical or virtual memory. Therefore, the total number of addresses to memory is often determined by the width of these registers. The IBM System/360 of the 1960s was an early 32-bit computer; it had 32-bit integer registers, although it only used the low order 24 bits of a word for addresses, resulting in a 16 MiB address space. 32-bit superminicomputers, such as the DEC VAX, became common in the 1970s, and 32-bit microprocessors, such as the Motorola 68000 family and the 32-bit members of the x86 family starting with the Intel 80386, appeared in the mid-1980s, making 32 bits something of a de facto consensus as a convenient register size.

A 32-bit address register meant that 232 addresses, or 4 GB of random-access memory (RAM), could be referenced. When these architectures were devised, 4 GB of memory was so far beyond the typical amounts (4 MiB) in installations, that this was considered to be enough headroom for addressing. 4.29 billion addresses were considered an appropriate size to work with for another important reason: 4.29 billion integers are enough to assign unique references to most entities in applications like databases.

Some supercomputer architectures of the 1970s and 1980s, such as the Cray-1,[2] used registers up to 64 bits wide, and supported 64-bit integer arithmetic, although they did not support 64-bit addressing. In the mid-1980s, Intel i860[3] development began culminating in a 1989 release; the i860 had 32-bit integer registers and 32-bit addressing, so it was not a fully 64-bit processor, although its graphics unit supported 64-bit integer arithmetic.[4] However, 32 bits remained the norm until the early 1990s, when the continual reductions in the cost of memory led to installations with amounts of RAM approaching 4 GB, and the use of virtual memory spaces exceeding the 4 GB ceiling became desirable for handling certain types of problems. In response, MIPS and DEC developed 64-bit microprocessor architectures, initially for high-end workstation and server machines. By the mid-1990s, HAL Computer Systems, Sun Microsystems, IBM, Silicon Graphics, and Hewlett-Packard had developed 64-bit architectures for their workstation and server systems. A notable exception to this trend were mainframes from IBM, which then used 32-bit data and 31-bit address sizes; the IBM mainframes did not include 64-bit processors until 2000. During the 1990s, several low-cost 64-bit microprocessors were used in consumer electronics and embedded applications. Notably, the Nintendo 64[5] and the PlayStation 2 had 64-bit microprocessors before their introduction in personal computers. High-end printers, network equipment, and industrial computers, also used 64-bit microprocessors, such as the Quantum Effect Devices R5000[6] . 64-bit computing started to trickle down to the personal computer desktop from 2003 onward, when some models in Apple's Macintosh lines switched to PowerPC 970 processors (termed G5 by Apple), and Advanced Micro Devices (AMD) released its first 64-bit x86-64 processor. Physical memory eventually caught up with 32 bit limits. In 2023, laptop computers were commonly equipped with 16GB and servers up to 64 GB of memory, greatly exceeding the 4 GB address capacity of 32 bits.

64-bit data timeline

1961: IBM delivers the IBM 7030 Stretch supercomputer, which uses 64-bit data words and 32- or 64-bit instruction words.
  • 1974: Control Data Corporation launches the CDC Star-100 vector supercomputer, which uses a 64-bit word architecture (prior CDC systems were based on a 60-bit architecture).
  • International Computers Limited launches the ICL 2900 Series with 32-bit, 64-bit, and 128-bit two's complement integers; 64-bit and 128-bit floating point; 32-bit, 64-bit, and 128-bit packed decimal and a 128-bit accumulator register. The architecture has survived through a succession of ICL and Fujitsu machines. The latest is the Fujitsu Supernova, which emulates the original environment on 64-bit Intel processors.
    1976: Cray Research delivers the first Cray-1 supercomputer, which is based on a 64-bit word architecture and will form the basis for later Cray vector supercomputers.
  • 1983: Elxsi launches the Elxsi 6400 parallel minisupercomputer. The Elxsi architecture has 64-bit data registers but a 32-bit address space.
  • 1989: Intel introduces the Intel i860 reduced instruction set computer (RISC) processor. Marketed as a "64-Bit Microprocessor", it had essentially a 32-bit architecture, enhanced with a 3D graphics unit capable of 64-bit integer operations.[7]
  • 1993: Atari introduces the Atari Jaguar video game console, which includes some 64-bit wide data paths in its architecture.[8]

    • 64-bit address timeline

    1991: MIPS Computer Systems produces the first 64-bit microprocessor, the R4000, which implements the MIPS III architecture, the third revision of its MIPS architecture.[9] The CPU is used in SGI graphics workstations starting with the IRIS Crimson. Kendall Square Research deliver their first KSR1 supercomputer, based on a proprietary 64-bit RISC processor architecture running OSF/1.
  • 1992: Digital Equipment Corporation (DEC) introduces the pure 64-bit Alpha architecture which was born from the PRISM project.[10]
  • 1994: Intel announces plans for the 64-bit IA-64 architecture (jointly developed with Hewlett-Packard) as a successor to its 32-bit IA-32 processors. A 1998 to 1999 launch date was targeted.
  • 1995: Sun launches a 64-bit SPARC processor, the UltraSPARC.[11] Fujitsu-owned HAL Computer Systems launches workstations based on a 64-bit CPU, HAL's independently designed first-generation SPARC64. IBM releases the A10 and A30 microprocessors, the first 64-bit PowerPC AS processors.[12] IBM also releases a 64-bit AS/400 system upgrade, which can convert the operating system, database and applications.
  • 1996: Nintendo introduces the Nintendo 64 video game console, built around a low-cost variant of the MIPS R4000. HP releases the first implementation of its 64-bit PA-RISC 2.0 architecture, the PA-8000.[13]
  • 1998: IBM releases the POWER3 line of full-64-bit PowerPC/POWER processors.[14]
  • 1999: Intel releases the instruction set for the IA-64 architecture. AMD publicly discloses its set of 64-bit extensions to IA-32, called x86-64 (later branded AMD64).
  • 2000: IBM ships its first 64-bit z/Architecture mainframe, the zSeries z900. z/Architecture is a 64-bit version of the 32-bit ESA/390 architecture, a descendant of the 32-bit System/360 architecture.
  • 2001: Intel ships its IA-64 processor line, after repeated delays in getting to market. Now branded Itanium and targeting high-end servers, sales fail to meet expectations.
  • 2003: AMD introduces its Opteron and Athlon 64 processor lines, based on its AMD64 architecture which is the first x86-based 64-bit processor architecture. Apple also ships the 64-bit "G5" PowerPC 970 CPU produced by IBM. Intel maintains that its Itanium chips would remain its only 64-bit processors.
  • 2004: Intel, reacting to the market success of AMD, admits it has been developing a clone of the AMD64 extensions named IA-32e (later renamed EM64T, then yet again renamed to Intel 64). Intel ships updated versions of its Xeon and Pentium 4 processor families supporting the new 64-bit instruction set.
  • VIA Technologies announces the Isaiah 64-bit processor.[15]
    2006: Sony, IBM, and Toshiba begin manufacturing the 64-bit Cell processor for use in the PlayStation 3, servers, workstations, and other appliances. Intel released Core 2 Duo as the first mainstream x86-64 processor for its mobile, desktop, and workstation line. Prior 64-bit extension processor lines were not widely available in the consumer retail market (most of 64-bit Pentium 4/D were OEM), 64-bit Pentium 4, Pentium D, and Celeron were not into mass production until late 2006 due to poor yield issue (most of good yield wafers were targeted at server and mainframe while mainstream still remain 130 nm 32-bit processor line until 2006) and soon became low end after Core 2 debuted. AMD released their first 64-bit mobile processor and manufactured in 90 nm.
  • 2011: ARM Holdings announces ARMv8-A, the first 64-bit version of the ARM architecture family.[16]
  • 2012: ARM Holdings announced their Cortex-A53 and Cortex-A57 cores, their first cores based on their 64-bit architecture, on 30 October 2012.[17] [18]
  • 2013:Apple announces the iPhone 5S, with the world's first 64-bit processor in a smartphone, which uses their A7 ARMv8-A-based system-on-a-chip alongside the iPad Air and iPad Mini 2 which are the world's first 64-bit processor in a tablet.
  • 2014:Google announces the Nexus 9 tablet, the first Android device to run on the 64-bit Tegra K1 chip.
  • 2015:Apple announces the iPod Touch (6th generation), the first iPod Touch to use the 64-bit processor A8 ARMv8-A-based system-on-a-chip alongside the Apple TV (4th generation) which is the world's first 64-bit processor in an Apple TV.
  • 2018:Apple announces the Apple Watch Series 4, the first Apple Watch to use the 64-bit processor S4 ARMv8-A-based system-on-a-chip.
  • 2020:Synopsis announce the ARCv3 ISA, the first 64-bit version of the ARC ISA.[19]

    • 64-bit operating system timeline

    1985: Cray releases UNICOS, the first 64-bit implementation of the Unix operating system.[20]
  • 1993: DEC releases the 64-bit DEC OSF/1 AXP Unix-like operating system (later renamed Tru64 UNIX) for its systems based on the Alpha architecture.
  • 1994: Support for the R8000 processor is added by Silicon Graphics to the IRIX operating system in release 6.0.
  • 1995: DEC releases OpenVMS 7.0, the first full 64-bit version of OpenVMS for Alpha. First 64-bit Linux distribution for the Alpha architecture is released.[21]
  • 1996: Support for the R4x00 processors in 64-bit mode is added by Silicon Graphics to the IRIX operating system in release 6.2.
  • 1998: Sun releases Solaris 7, with full 64-bit UltraSPARC support.
  • 2000: IBM releases z/OS, a 64-bit operating system descended from MVS, for the new zSeries 64-bit mainframes; 64-bit Linux on z Systems follows the CPU release almost immediately.
  • 2001: Linux becomes the first OS kernel to fully support x86-64 (on a simulator, as no x86-64 processors had been released yet).[22]
  • 2001: Microsoft releases Windows XP 64-Bit Edition for the Itanium's IA-64 architecture; it could run 32-bit applications through an execution layer.
  • 2003: Apple releases its Mac OS X 10.3 "Panther" operating system which adds support for native 64-bit integer arithmetic on PowerPC 970 processors.[23] Several Linux distributions release with support for AMD64. FreeBSD releases with support for AMD64.
  • 2005: On January 4, Microsoft discontinues Windows XP 64-Bit Edition, as no PCs with IA-64 processors had been available since the previous September, and announces that it is developing x86-64 versions of Windows to replace it.[24] On January 31, Sun releases Solaris 10 with support for AMD64 and EM64T processors. On April 29, Apple releases Mac OS X 10.4 "Tiger" which provides limited support for 64-bit command-line applications on machines with PowerPC 970 processors; later versions for Intel-based Macs supported 64-bit command-line applications on Macs with EM64T processors. On April 30, Microsoft releases Windows XP Professional x64 Edition and Windows Server 2003 x64 Edition for AMD64 and EM64T processors.[25]
  • 2006: Microsoft releases Windows Vista, including a 64-bit version for AMD64/EM64T processors that retains 32-bit compatibility. In the 64-bit version, all Windows applications and components are 64-bit, although many also have their 32-bit versions included for compatibility with plug-ins.
  • 2007: Apple releases Mac OS X 10.5 "Leopard", which fully supports 64-bit applications on machines with PowerPC 970 or EM64T processors.
  • 2009: Microsoft releases Windows 7, which, like Windows Vista, includes a full 64-bit version for AMD64/Intel 64 processors; most new computers are loaded by default with a 64-bit version. Microsoft also releases Windows Server 2008 R2, which is the first 64-bit only server operating system. Apple releases Mac OS X 10.6, "Snow Leopard", which ships with a 64-bit kernel for AMD64/Intel64 processors, although only certain recent models of Apple computers will run the 64-bit kernel by default. Most applications bundled with Mac OS X 10.6 are now also 64-bit.[23]
  • 2011: Apple releases Mac OS X 10.7, "Lion", which runs the 64-bit kernel by default on supported machines. Older machines that are unable to run the 64-bit kernel run the 32-bit kernel, but, as with earlier releases, can still run 64-bit applications; Lion does not support machines with 32-bit processors. Nearly all applications bundled with Mac OS X 10.7 are now also 64-bit, including iTunes.
  • 2012: Microsoft releases Windows 8 which supports UEFI Class 3 (UEFI without CSM) and Secure Boot.[26]
  • 2013: Apple releases iOS 7, which, on machines with AArch64 processors, has a 64-bit kernel that supports 64-bit applications.
  • 2014: Google releases Android Lollipop, the first version of the Android operating system with support for 64-bit processors.
  • 2017: Apple releases iOS 11, supporting only machines with AArch64 processors. It has a 64-bit kernel that only supports 64-bit applications. 32-bit applications are no longer compatible.
  • 2018: Apple releases watchOS 5, the first watchOS version to bring the 64-bit support.
  • 2019: Apple releases macOS 10.15 "Catalina", dropping support for 32-bit Intel applications.
  • 2021: Microsoft releases Windows 11 on October 5, which only supports 64-bit systems, dropping support for IA-32 systems.
  • 2022: Google releases the Pixel 7, which drops support for non-64-bit applications. Apple releases watchOS 9, the first watchOS version to run exclusively on the Apple Watch models with 64-bit processors (including Apple Watch Series 4 or newer, Apple Watch SE (1st generation) or newer and the newly introduced Apple Watch Ultra), dropping support for Apple Watch Series 3 as the final Apple Watch model with 32-bit processor.

    • Limits of processors

    In principle, a 64-bit microprocessor can address 16 EB (

    Notes and References

    1. Book: Pentium Processor User's Manual Volume 1: Pentium Processor Data Book. Intel. 1993.
    2. Web site: Cray-1 Computer System Hardware Reference Manual. Cray Research. 1977. October 8, 2013.
    3. Jack . Grimes . Les . Kohn . Rajeev . Bharadhwaj . The Intel i860 64-Bit Processor: A General-Purpose CPU with 3D Graphics Capabilities . July–August 1989 . 9 . 4 . 85–94. 2010-11-19 . 10.1109/38.31467 . IEEE Computer Graphics and Applications . 38831149.
    4. Web site: i860 Processor Family Programmer's Reference Manual. Intel. 1991. September 12, 2019.
    5. NEC Offers Two High Cost Performance 64-bit RISC Microprocessors. NEC. 1998-01-20. 2011-01-09. Versions of the VR4300 processor are widely used in consumer and office automation applications, including the popular Nintendo 64TM video game and advanced laser printers such as the recently announced, award-winning Hewlett-Packard LaserJet 4000 printer family..
    6. MIPS R5000 Microprocessor Technical Backgrounder. MIPS Technologies, Inc. 2024-08-19.
    7. Web site: i860 64-Bit Microprocessor. Intel. 30 November 2010. 1989.
    8. Web site: Atari Jaguar History . AtariAge.
    9. Book: Joe Heinrich . MIPS R4000 Microprocessor User's Manual . 2nd . 1994 . MIPS Technologies, Inc..
    10. Richard L. Sites . Alpha AXP Architecture . Digital Technical Journal . 4 . 4 . 1992 . Digital Equipment Corporation.
    11. Gwennap . Linley . UltraSparc Unleashes SPARC Performance . Microprocessor Report . 8 . 13 . 3 October 1994 . MicroDesign Resources.
    12. Bishop . J. W. . etal . PowerPC AS A10 64-bit RISC microprocessor . IBM Journal of Research and Development . 40 . 4 . July 1996 . 495–505 . IBM Corporation . 10.1147/rd.404.0495.
    13. Gwennap . Linley . PA-8000 Combines Complexity and Speed . Microprocessor Report . 8 . 15 . 14 November 1994 . MicroDesign Resources.
    14. F. P. O'Connell . S. W. White . POWER3: The next generation of PowerPC processors . IBM Journal of Research and Development . 44 . 6 . November 2000 . 873–884 . IBM Corporation . 10.1147/rd.446.0873.
    15. Web site: VIA Unveils Details of Next-Generation Isaiah Processor Core. VIA Technologies, Inc.. 2007-07-18. dead . https://web.archive.org/web/20071011053054/http://via.com.tw/en/resources/pressroom/2004_archive/pr041005_fpf-isaiah.jsp. 2007-10-11.
    16. Web site: ARMv8 Technology Preview. October 31, 2011. November 15, 2012. November 11, 2011. https://web.archive.org/web/20111111161327/https://www.arm.com/files/downloads/ARMv8_Architecture.pdf. dead.
    17. ARM Launches Cortex-A50 Series, the World's Most Energy-Efficient 64-bit Processors . . 2012-10-31.
    18. Web site: ARM Keynote: ARM Cortex-A53 and ARM Cortex-A57 64bit ARMv8 processors launched. ARMdevices.net . 2012-10-31 .
    19. Web site: Synopsys Introduces New 64-bit ARC Processor IP . live . https://web.archive.org/web/20220331110658/https://news.synopsys.com/2020-04-07-Synopsys-Introduces-New-64-bit-ARC-Processor-IP-Delivering-Up-to-3x-Performance-Increase-for-High-End-Embedded-Applications . 31 March 2022.
    20. Web site: Stefan Berka . Unicos Operating System . www.operating-system.org . 2010-11-19 . https://web.archive.org/web/20101126033526/http://operating-system.org/betriebssystem/_english/bs-unicos.htm . 26 November 2010 . live.
    21. My Life and Free Software. Jon "maddog" Hall. Jon Hall (programmer). Jun 1, 2000. Linux Journal.
    22. Porting Linux to x86-64 . Andi Kleen . Status: The kernel, compiler, tool chain work. The kernel boots and work on simulator and is used for porting of userland and running programs . Ottawa Linux Symposium 2001.
    23. Web site: Mac OS X 10.6 Snow Leopard: the Ars Technica review . 5 . John Siracusa . Ars Technica . September 2009 . 2009-09-06 . https://web.archive.org/web/20091009161632/http://arstechnica.com/apple/reviews/2009/08/mac-os-x-10-6.ars/5 . 9 October 2009 . live.
    24. Web site: Microsoft nixes Windows XP for Itanium. 5 January 2005. Joris Evers. Computerworld. 17 October 2017. https://web.archive.org/web/20130618025711/http://www.computerworld.com/s/article/98716/Microsoft_nixes_Windows_XP_for_Itanium?taxonomyId=125. 18 June 2013 . dead.
    25. Microsoft Raises the Speed Limit with the Availability of 64-Bit Editions of Windows Server 2003 and Windows XP Professional . Microsoft . April 25, 2005 . September 10, 2015.
    26. Web site: UEFI_on_Dell BizClient_Platforms.

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