Editing 64-bit computing (section)

=== 32-bit vs 64-bit ===
A change from a [[32-bit computing|32-bit]] to a 64-bit architecture is a fundamental alteration, as most [[operating system]]s must be extensively modified to take advantage of the new architecture, because that software has to manage the actual memory addressing hardware.<ref>{{cite journal |title=The Long Road to 64 Bits |date=October 2006 |volume=4 |issue=8 |pages=85–94|first=John |last=Mashey |journal=ACM Queue|doi=10.1145/1165754.1165766 |doi-access=free}}</ref> Other software must also be [[Porting|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 [[emulator|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.<ref>{{cite web |title=Windows 7: 64 bit vs 32 bit? |date=2 April 2009 |url=https://www.w7forums.com/threads/windows-7-64-bit-vs-32-bit.484/ |url-status=live |archive-url=https://web.archive.org/web/20090405053428/https://www.w7forums.com/windows-7-64-bit-vs-32-bit-t484.html |archive-date=5 April 2009 |access-date=2009-04-05 |publisher=W7 Forums}}</ref>

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 [[database]]s easier, there has been considerable debate on whether they or their 32-bit [[compatibility mode]]s 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 <code>char</code>, <code>short</code>, <code>int</code>, <code>long</code>, <code>float</code>, and <code>double</code>, 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.<ref>{{cite web
| title= Frequently Asked Questions About the Java HotSpot VM
| publisher=Oracle
| url=https://www.oracle.com/java/technologies/hotspotfaq.html
| access-date= 2024-12-13}}</ref>

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.