64-bit operating systems are designed to be backwards compatible with 32-bit applications, and if there is no real expected benefit for a particular software, the developer of the software may just as well decide to stick with 32-bit and avoid the efforts and costs that it would take to make the change to 64-bit or even support multiple versions of the software. 64) you would very easily hit the 32-bit 4GB limit as you would only be able to allocate 62.5MB of RAM per processor from your code.Įven with hardware architectures and operating systems mainly being 64-bit these days, a lot of software still is only available as 32-bit versions. If you had a machine with more processors (e.g. For example if you had 8 tasks that all needed 500MB of RAM each – that’s very close to the 4GB limit in total (500MB * 8 = 4000MB). While in principle, you can move larger amounts of data per time between memory and CPU with 64-bit, this typically doesn't result in significantly improved execution times because of caching and other optimization techniques used by modern CPUs. However if we start using programming models where we run many tasks at once, you might want more than 4GB allocated to those processes. There most likely won't be any innate performance benefits to be gained by moving from 32-bit and 64-bit unless you need that extra memory. Technically with a 64-bit architecture you could access 16 Exabytes of memory (2^64) and while not wanting to paraphrase Bill Gates, that is probably more than we’ll need for the foreseeable future. If the file system of your operating system is limited to 32-bit integers as well, this also means you cannot have any single file larger than 4GB either in memory or on disk (you can still page or chain larger files together though).Ħ4-bit architectures don’t have this limit. Instead you can access up to 16 terabytes of memory and this is actually only the limit of current chip architectures which "only" use 44 bits which will change over time as software and hardware architectures evolve. 32-bit software or hardware can only directly represent and operate with numbers up to 2^32 and, hence, can only address up to a maximum of 4GB of memory (that is 2^32 = 4294967296 bytes).
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