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ince the previous september and announces that it is developing x86 64 versions of windows to replace it 27 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 28 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 citation needed 2007 apple releases mac os x 10 5 leopard which fully supports 64 bit applications on machines with powerpc 970 or em64t processors citation needed 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 26 2010 windows 7 64 bit becomes the most popular os on steam surpassing windows xp 32 bit 29 30 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 citation needed 2012 microsoft releases windows 8 which supports uefi class 3 uefi without csm and secure boot 31 apple releases os x mountain lion which makes the 64 bit kernel the default on some older previously unsupported machines and removes the 32 bit kernel 2018 apple releases watchos 5 the first watchos version to bring the 64 bit support citation needed 2019 apple releases macos 10 15 catalina dropping support for 32 bit intel applications citation needed 2021 microsoft releases windows 11 on october 5 which only supports 64 bit systems dropping support for ia 32 and aarch32 systems citation needed 2022 google releases the pixel 7 which drops support for 32 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 citation needed 2023 google releases android 14 which drops support for 32 bit applications 2024 microsoft releases windows 11 2024 update arm versions of which drop support for 32 bit arm applications 2025 2026 google limits of processors edit in principle a 64 bit microprocessor can address 16 eb 16 1024 6 2 64 18 446 744 073 709 551 616 bytes of memory however not all instruction sets and not all processors implementing those instruction sets support a full 64 bit virtual or physical address space the x86 64 architecture as of march 2024 update allows 48 bits for virtual memory and for any given processor up to 52 bits for physical memory 32 33 these limits allow memory sizes of 256 tb 256 1024 4 bytes and 4 pb 4 1024 5 bytes respectively a pc cannot currently contain 4 petabytes of memory due to the physical size of the memory chips but amd envisioned large servers shared memory clusters and other uses of physical address space that might approach this in the foreseeable future thus the 52 bit physical address provides ample room for expansion while not incurring the cost of implementing full 64 bit physical addresses similarly the 48 bit virtual address space was designed to provide 65 536 2 16 times the 32 bit limit of 4 gb 4 1024 3 bytes allowing room for later expansion and incurring no overhead of translating full 64 bit addresses the power isa v3 0 allows 64 bits for an effective address mapped to a segmented address with between 65 and 78 bits allowed for virtual memory and for any given processor up to 60 bits for physical memory 34 the oracle sparc architecture 2015 allows 64 bits for virtual memory and for any given processor between 40 and 56 bits for physical memory 35 the arm aarch64 virtual memory system architecture allows from 48 to 56 bits for virtual memory and for any given processor from 32 to 56 bits for physical memory 36 the dec alpha specification requires minimum of 43 bits of virtual memory address space 8 tb to be and hardware need to check and trap if the remaining unsupported bits are zero to support compatibility on future processors alpha 21064 supported 43 bits of virtual memory address space 8 tb and 34 bits of physical memory address space 16 gb alpha 21164 supported 43 bits of virtual memory address space 8 tb and 40 bits of physical memory address space 1 tb alpha 21264 supported user configurable 43 or 48 bits of virtual memory address space 8 tb or 256 tb and 44 bits of physical memory address space 16 tb 64 bit applications edit 32 bit vs 64 bit edit a change from a 32 bit to a 64 bit architecture is a fundamental alteration as most operating systems must be extensively modified to take advantage of the new architecture because that software has to manage the actual memory addressing hardware 37 other software must also be ported to use the new abilities older 32 bit software may be supported either by virtue of the 64 bit instruction set being a superset of the 32 bit instruction set so that processors that support the 64 bit instruction set can also run code for the 32 bit instruction set or through software emulation or by the actual implementation of a 32 bit processor core within the 64 bit processor as with some itanium processors from intel which included an ia 32 processor core to run 32 bit x86 applications the operating systems for those 64 bit architectures generally support both 32 bit and 64 bit applications 38 one significant exception to this is the ibm as 400 software for which is compiled into a virtual instruction set architecture isa called technology independent machine interface timi timi code is then translated to native machine code by low level software before being executed the translation software is all that must be rewritten to move the full os and all software to a new platform as when ibm transitioned the native instruction set for as 400 from the older 32 48 bit impi to the newer 64 bit powerpc as codenamed amazon the impi instruction set was quite different from even 32 bit powerpc so this transition was even bigger than moving a given instruction set from 32 to 64 bits on 64 bit hardware with x86 64 architecture amd64 most 32 bit operating systems and applications can run with no compatibility issues while the larger address space of 64 bit architectures makes working with large data sets in applications such as digital video scientific computing and large databases easier there has been considerable debate on whether they or their 32 bit compatibility modes will be faster than comparably priced 32 bit systems for other tasks a compiled java program can run on a 32 or 64 bit java virtual machine with no modification the lengths and precision of all the built in types such as char short int long float and double and the types that can be used as array indices are specified by the standard and are not dependent on the underlying architecture java programs that run on a 64 bit java virtual machine have access to a larger address space 39 speed is not the only factor to consider in comparing 32 bit and 64 bit processors applications such as multi tasking stress testing and clustering for high performance computing hpc may be more suited to a 64 bit architecture when deployed appropriately for this reason 64 bit clusters have been widely deployed in large organizations such as ibm hp and microsoft summary a 64 bit processor performs best with 64 bit software a 64 bit processor may have backward compatibility allowing it to run 32 bit application software for the 32 bit version of its instruction set and may also support running 32 bit operating systems for the 32 bit version of its instruction set a 32 bit processor is incompatible with 64 bit software pros and cons edit a common misconception is that 64 bit architectures are no better than 32 bit architectures unless the computer has more than 4 gb of random access memory 40 this is not entirely true some operating systems and certain hardware configurations limit the physical memory space to 3 gb on ia 32 systems due to much of the 3 4 gb region being reserved for hardware addressing see 3 gb barrier 64 bit architectures can address far more than 4 gb however ia 32 processors from the pentium pro onward allow a 36 bit physical memory address space using physical address extension pae which gives a 64 gb physical address range of which up to 62 gb may be used by main memory operating systems that support pae may not be limited to 4 gb of physical memory even on ia 32 processors however drivers and other kernel mode software more so older versions may be incompatible with pae this has been cited as the reason for 32 bit versions of microsoft windows being limited to 4 gb of physical ram 41 although the validity of this explanation has been disputed 42 some operating systems reserve portions of process address space for os use effectively reducing the total address space available for mapping memory for user programs for instance 32 bit windows reserves 1 or 2 gb depending on the settings of the total address space for the kernel which leaves only 3 or 2 gb respectively of the address space available for user mode this limit is much higher on 64 bit operating systems memory mapped files are becoming more difficult to implement in 32 bit architectures as files of over 4 gb become more common such large files cannot be memory mapped easily to 32 bit architectures as only part of the file can be mapped into the address space at a time and to access such a file by memory mapping the parts mapped must be swapped into and out of the address space as needed this is a problem as memory mapping if properly implemented by the os is one of the most efficient disk to memory methods some 64 bit programs such as encoders decoders and encryption software can benefit greatly from 64 bit registers citation needed while the performance of other programs such as 3d graphics oriented ones remains unaffected when switching from a 32 bit to a 64 bit environment citation needed some 64 bit architectures such as x86 64 and aarch64 support more general purpose registers than their 32 bit counterparts although this is not due specifically to the word length this leads to a significant speed increase for tight loops since the processor does not have to fetch data from the cache or main memory if the data can fit in the available registers example in c int a b c d e for a 0 a 100 a b a c b d c e d this code first creates 5 values a b c d and e and then puts them in a loop during the loop this code changes the value of b to the value of a the value of c to the value of b the value of d to the value of c and the value of e to the value of d this has the same effect as changing all the values to a if a processor can keep only two or three values or variables in registers it would need to move some values between memory and registers to be able to process variables d and e also this is a process that takes many cpu cycles a processor that can hold all values and variables in registers can loop through them with no need to move data between registers and memory for each iteration this behavior can easily be compared with virtual memory although any effects are contingent on the compiler the main disadvantage of 64 bit architectures is that relative to 32 bit architectures the same data occupies more space in memory due to longer pointers and possibly other types and alignment padding this increases the memory requirements of a given process and can have implications for efficient processor cache use maintaining a partial 32 bit model is one way to handle this and is in general reasonably effective for example the z os operating system takes this approach requiring program code to reside in 31 bit address spaces the high order bit is not used in address calculation on the underlying hardware platform while data objects can optionally reside in 64 bit regions not all such applications require a large address space or manipulate 64 bit data items so these applications do not benefit from these features software availability edit x86 based 64 bit systems sometimes lack equivalents of software that is written for 32 bit architectures the most severe problem in microsoft windows is incompatible device drivers for obsolete hardware most 32 bit application software can run on a 64 bit operating system in a compatibility mode also termed an emulation mode e g microsoft wow64 technology for ia 64 and amd64 the 64 bit windows native mode 43 driver environment runs atop 64 bit ntdll dll which cannot call 32 bit win32 subsystem code often devices whose actual hardware function is emulated in user mode software like winprinters because 64 bit drivers for most devices were unavailable until early 2007 vista x64 using a 64 bit version of windows was considered a challenge however the trend has since moved toward 64 bit computing more so as memory prices dropped and the use of more than 4 gb of ram increased most manufacturers started to provide both 32 bit and 64 bit drivers for new devices so unavailability of 64 bit drivers ceased to be a problem 64 bit drivers were not provided for many older devices which could consequently not be used in 64 bit systems driver compatibility was less of a problem with open source drivers as 32 bit ones could be modified for 64 bit use support for hardware made before early 2007 was problematic for open source platforms citation needed due to the relatively small number of users 64 bit versions of windows cannot run 16 bit software however most 32 bit applications will work well 64 bit users are forced to install a virtual machine of a 16 or 32 bit operating system to run 16 bit applications or use one of the alternatives for ntvdm 44 mac os x 10 4 tiger and mac os x 10 5 leopard had only a 32 bit kernel but they can run 64 bit user mode code on 64 bit processors mac ...