<span class="mw-page-title-main">64-bit computing</span>

64-bit computing

<p>In <a href="/en/Computer_architecture" title="Computer architecture" class="wl">computer architecture</a>, <b>64-bit</b> <a href="/en/Integer_(computer_science)" title="Integer (computer science)" class="wl">integers</a>, <a href="/en/Memory_address" title="Memory address" class="wl">memory addresses</a>, or other <a href="/en/Data_(computing)" title="Data (computing)" class="mw-redirect wl">data</a> units<span class="mw-ref reference" id="cite_ref-1"><a href="#cite_note-1" style="counter-reset: mw-Ref 1;" data-mw-group="lower-alpha"><span class="mw-reflink-text">[lower-alpha 1]</span></a></span> are those that are 64 <a href="/en/Bit" title="Bit" class="wl">bits</a> wide. Also, 64-bit <a href="/en/Central_processing_unit" title="Central processing unit" class="wl">CPUs</a> and <a href="/en/Arithmetic_logic_unit" title="Arithmetic logic unit" class="wl">ALUs</a> are those that are based on <a href="/en/Processor_register" title="Processor register" class="wl">processor registers</a>, <a href="/en/Address_bus" title="Address bus" class="mw-redirect wl">address buses</a>, or <a href="/en/Bus_(computing)" title="Bus (computing)" class="wl">data buses</a> of that size.  A <a href="/en/Computer" title="Computer" class="wl">computer</a> that uses such a processor is a 64-bit computer. </p>

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Computer architecture bit width</div>
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<a href="/en/Word_(computer_architecture)" title="Word (computer architecture)" class="wl">Bit</a></th></tr><tr><td class="sidebar-content">
<div class="hlist"><ul><li><a href="/en/1-bit_computing" title="1-bit computing" class="wl">1</a></li><li><a href="/en/4-bit_computing" title="4-bit computing" class="wl">4</a></li><li><a href="/en/8-bit_computing" title="8-bit computing" class="wl">8</a></li><li><a href="/en/12-bit_computing" title="12-bit computing" class="wl">12</a></li><li><a href="/en/16-bit_computing" title="16-bit computing" class="wl">16</a></li><li><a href="/en/18-bit_computing" title="18-bit computing" class="wl">18</a></li><li><a href="/en/24-bit_computing" title="24-bit computing" class="wl">24</a></li><li><a href="/en/26-bit_computing" title="26-bit computing" class="wl">26</a></li><li><a href="/en/28-bit_computing" title="28-bit computing" class="wl">28</a></li><li><a href="/en/UNIVAC_490" title="UNIVAC 490" class="wl">30</a></li><li><a href="/en/31-bit_computing" title="31-bit computing" class="wl">31</a></li><li><a href="/en/32-bit_computing" title="32-bit computing" class="wl">32</a></li><li><a href="/en/36-bit_computing" title="36-bit computing" class="wl">36</a></li><li><a href="/en/45-bit_computing" title="45-bit computing" class="wl">45</a></li><li><a href="/en/48-bit_computing" title="48-bit computing" class="wl">48</a></li><li><a href="/en/60-bit_computing" title="60-bit computing" class="wl">60</a></li><li><a href="/en/64-bit_computing" title="64-bit computing" class="wl">64</a></li><li><a href="/en/128-bit_computing" title="128-bit computing" class="wl">128</a></li><li><a href="/en/256-bit_computing" title="256-bit computing" class="wl">256</a></li><li><a href="/en/512-bit_computing" title="512-bit computing" class="wl">512</a></li><li><a href="/en/Bit_slicing" title="Bit slicing" class="wl">bit slicing</a></li></ul></div></td>
</tr><tr><th class="sidebar-heading notheme" style="background-color: #ccccff;">
<a href="/en/Application_software" title="Application software" class="wl">Application</a></th></tr><tr><td class="sidebar-content">
<div class="hlist"><ul><li><a href="/en/8-bit_computing" title="8-bit computing" class="wl">8</a></li><li><a href="/en/16-bit_computing#16-bit_application" title="16-bit computing" class="wl">16</a></li><li><a href="/en/32-bit_computing#32-bit_application" title="32-bit computing" class="wl">32</a></li><li><a href="#64-bit_applications" title="64-bit computing" target="_blank">64</a></li></ul></div></td>
</tr><tr><th class="sidebar-heading notheme" style="background-color: #ccccff;">
<a href="/en/Floating-point_arithmetic" title="Floating-point arithmetic" class="wl">Binary floating-point</a> <a href="/en/Precision_(computer_science)" title="Precision (computer science)" class="wl">precision</a></th></tr><tr><td class="sidebar-content">
<div class="hlist"><ul><li><a href="/en/Half-precision_floating-point_format" title="Half-precision floating-point format" class="wl">16</a> (×½)</li><li><a href="/en/Minifloat" title="Minifloat" class="wl">24</a></li><li><a href="/en/Single-precision_floating-point_format" title="Single-precision floating-point format" class="wl">32</a> (×1)</li><li><a href="/en/Extended_precision" title="Extended precision" class="wl">40</a></li><li><a href="/en/Double-precision_floating-point_format" title="Double-precision floating-point format" class="wl">64</a> (×2)</li><li><a href="/en/Extended_precision" title="Extended precision" class="wl">80</a></li><li><a href="/en/Quadruple-precision_floating-point_format" title="Quadruple-precision floating-point format" class="wl">128</a> (×4)</li><li><a href="/en/Octuple-precision_floating-point_format" title="Octuple-precision floating-point format" class="wl">256</a> (×8)</li></ul></div></td>
</tr><tr><th class="sidebar-heading notheme" style="background-color: #ccccff;">
<a href="/en/Decimal_floating_point" title="Decimal floating point" class="wl">Decimal floating-point</a> <a href="/en/Precision_(computer_science)" title="Precision (computer science)" class="wl">precision</a></th></tr><tr><td class="sidebar-content">
<div class="hlist"><ul><li><a href="/en/Decimal32_floating-point_format" title="Decimal32 floating-point format" class="wl">32</a></li><li><a href="/en/Decimal64_floating-point_format" title="Decimal64 floating-point format" class="wl">64</a></li><li><a href="/en/Decimal128_floating-point_format" title="Decimal128 floating-point format" class="wl">128</a></li></ul></div></td>
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<p>From the software perspective, 64-bit computing means the use of <a href="/en/Machine_code" title="Machine code" class="wl">machine code</a> with 64-bit <a href="/en/Virtual_memory" title="Virtual memory" class="wl">virtual memory</a> addresses. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses; <a href="/en/X86-64" title="X86-64" class="wl">x86-64</a> and <a href="/en/ARMv8" title="ARMv8" class="mw-redirect wl">ARMv8</a>, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, and several 64-bit instruction sets support fewer than 64 bits of physical memory address.</p>

<p>The term <i>64-bit</i> also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a <a href="/en/Word_(computer_architecture)" title="Word (computer architecture)" class="wl">word</a> 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 <a href="/en/Supercomputer" title="Supercomputer" class="wl">supercomputers</a> since the 1970s (<a href="/en/Cray-1" title="Cray-1" class="wl">Cray-1</a>, 1975) and in <a href="/en/Reduced_instruction_set_computer" title="Reduced instruction set computer" class="wl">reduced instruction set computers</a> (RISC) based <a href="/en/Workstation" title="Workstation" class="wl">workstations</a> and <a href="/en/Server_(computing)" title="Server (computing)" class="wl">servers</a> since the early 1990s. In 2003, 64-bit CPUs were introduced to the mainstream <a href="/en/Personal_computer" title="Personal computer" class="wl">PC</a> market in the form of <a href="/en/X86-64" title="X86-64" class="wl">x86-64</a> processors and the <a href="/en/PowerPC_970" title="PowerPC 970" class="wl">PowerPC G5</a>.</p>

<p>A 64-bit register can hold any of 2<sup>64</sup> (over 18 <a href="/en/Quintillion" title="Quintillion" class="mw-redirect wl">quintillion</a> or 1.8×10<sup>19</sup>) different values. The range of <a href="/en/Integer" title="Integer" class="wl">integer</a> values that can be stored in 64 bits depends on the <a href="/en/Integer_(computer_science)#Value_and_representation" title="Integer (computer science)" class="wl">integer representation</a> used. With the two most common representations, the range is 0 through 18,446,744,073,709,551,615 (2<sup>64</sup> − 1) for representation as an (<a href="/en/Signedness" title="Signedness" class="wl">unsigned</a>) <a href="/en/Binary_number" title="Binary number" class="wl">binary number</a>, and −9,223,372,036,854,775,808 (−2<sup>63</sup>) through 9,223,372,036,854,775,807 (2<sup>63</sup> − 1) for representation as <a href="/en/Two's_complement" title="Two's complement" class="wl">two's complement</a>. Hence, a processor with 64-bit memory addresses can directly access 2<sup>64</sup> bytes (16 <a href="/en/Exbibytes" title="Exbibytes" class="mw-redirect wl">exbibytes</a> or EiB) of <a href="/en/Byte_addressing" title="Byte addressing" class="wl">byte-addressable</a> memory.</p>

<p>With no further qualification, a <i>64-bit computer architecture</i> generally has integer and addressing <a href="/en/Processor_register" title="Processor register" class="wl">registers</a> that are 64 bits wide, allowing direct support for 64-bit data types and addresses. However, a CPU might have external <a href="/en/Bus_(computing)" title="Bus (computing)" class="wl">data buses</a> or <a href="/en/Address_bus" title="Address bus" class="mw-redirect wl">address buses</a> with different sizes from the registers, even larger (the 32-bit <a href="/en/Pentium" title="Pentium" class="wl">Pentium</a> had a 64-bit data bus, for instance).<span class="mw-ref reference" id="cite_ref-2"><a href="#cite_note-2" style="counter-reset: mw-Ref 1;"><span class="mw-reflink-text">[1]</span></a></span></p>



In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs 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 ARMv8, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, 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 and in reduced instruction set computers 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. 