Are 64 bit programs bigger and faster than 32 bit versions

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I suppose I am focussing on x86  but I am generally interested in the move from 32 to 64 bit   Logically  I can see that constants and pointers  in some cases  will be larger so programs are likely to be larger  And the desire to allocate memory on word boundaries for efficiency would mean more white-space between allocations   I have also heard that 32 bit mode on the x86 has to flush its cache when context switching due to possible overlapping 4G address spaces   So  what are the real benefits of 64 bit   And as a supplementary question  would 128 bit be even better    Edit   I have just written my first 32 64 bit program  It makes linked lists trees of 16 byte  32b version  or 32 byte  64b version  objects and does a lot of printing to stderr - not a really useful program  and not something typical  but it is my first   Size  81128 32b  v 83672 64b  - so not much difference  Speed  17s 32b  v 24s 64b  - running on 32 bit OS  OS-X 10 5 8   Update   I note that a new hybrid x32 ABI  Application Binary Interface  is being developed that is 64b but uses 32b pointers  For some tests it results in smaller code and faster execution than either 32b or 64b    https   sites google com site x32abi

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In the specific case of x68 to x68 64  the 64 bit program will be about the same size  if not slightly smaller  use a bit more memory  and run faster   Mostly this is because x86 64 doesn t just have 64 bit registers  it also has twice as many   x86 does not have enough registers to make compiled languages as efficient as they could be  so x86 code spends a lot of instructions and memory bandwidth shifting data back and forth between registers and memory   x86 64 has much less of that  and so it takes a little less space and runs faster   Floating point and bit-twiddling vector instructions are also much more efficient in x86 64   In general  though  64 bit code is not necessarily any faster  and is usually larger  both for code and memory usage at runtime

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Any applications that require CPU usage such as transcoding  display performance and media rendering  whether it be audio or visual  will certainly require  at this point  and benefit from using 64 bit versus 32 bit due to the CPU s ability to deal with the sheer amount of data being thrown at it  It s not so much a question of address space as it is the way the data is being dealt with  A 64 bit processor  given 64 bit code  is going to perform better  especially with mathematically difficult things like transcoding and VoIP data - in fact  any sort of  math  applications should benefit by the usage of 64 bit CPUs and operating systems  Prove me wrong

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I typically see a 30  speed improvement for compute-intensive code on x86-64 compared to x86  This is most likely due to the fact that we have 16 x 64 bit general purpose registers and 16 x SSE registers instead of 8 x 32 bit general purpose registers and 8 x SSE registers  This is with the Intel ICC compiler  11 1  on an x86-64 Linux - results with other compilers  e g  gcc   or with other operating systems  e g  Windows   may be different of course

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Unless you need to access more memory that 32b addressing will allow you  the benefits will be small  if any   When running on 64b CPU  you get the same memory interface no matter if you are running 32b or 64b code  you are using the same cache and same BUS    While x64 architecture has a few more registers which allows easier optimizations  this is often counteracted by the fact pointers are now larger and using any structures with pointers results in a higher memory traffic  I would estimate the increase in the overall memory usage for a 64b application compared to a 32b one to be around 15-30

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In addition to having more registers  64-bit has SSE2 by default  This means that you can indeed perform some calculations in parallel  The SSE extensions had other goodies too  But I guess the main benefit is not having to check for the presence of the extensions  If it s x64  it has SSE2 available     If my memory serves me correctly

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Regardless of the benefits  I would suggest that you always compile your program for the system s default word size  32-bit or 64-bit   since if you compile a library as a 32-bit binary and provide it on a 64-bit system  you will force anyone who wants to link with your library to provide their library  and any other library dependencies  as a 32-bit binary  when  the 64-bit version is the default available   This can be quite a nuisance for everyone  When in doubt  provide both versions of your library   As to the practical benefits of 64-bit    the most obvious is that you get a bigger address space  so if mmap a file  you can address more of it at once  and load larger files into memory   Another benefit is that  assuming the compiler does a good job of optimizing  many of your arithmetic operations can be parallelized  for example  placing two pairs of 32-bit numbers in two registers and performing two adds in single add operation   and big number computations will run more quickly  That said  the whole 64-bit vs 32-bit thing won t help you with asymptotic complexity at all  so if you are looking to optimize your code  you should probably be looking  at the algorithms rather than the constant factors like this   EDIT  Please disregard my statement about the parallelized addition  This is not performed by an ordinary add statement    I was confusing that with some of the vectorized SSE instructions  A more accurate benefit  aside from the larger address space  is that there are more general purpose registers  which means more local variables can be maintained in the CPU register file  which is much faster to access  than if you place the variables in the program stack  which usually means going out to the L1 cache

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Only justification for moving your application to 64 bit is need for more memory in applications like large databases or ERP applications with at least 100s of concurrent users where 2 GB limit will be exceeded fairly quickly when applications cache for better performance  This is case specially on Windows OS where integer and long is still 32 bit  they have new variable  int64  Only pointers are 64 bit  In fact WOW64 is highly optimised on Windows x64 so that 32 bit applications run with low penalty on 64 bit Windows OS  My experience on Windows x64 is 32 bit application version run 10-15  faster than 64 bit since in former case at least for proprietary memory databases you can use pointer arithmatic  for maintaining b-tree  most processor intensive part of database systems   Compuatation intensive applications which require large decimals for highest accuracy not afforded by double on 32-64 bit operating system  These applications can use  int64 in natively instead of software emulation  Of course large disk based databases will also show improvement over 32 bit simply due to ability to use large memory for caching query plans and so on

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I m coding a chess engine named foolsmate  The best move extraction using a minimax-based tree search to depth 9  from a certain position  took   on Win32 configuration   17 0s   after switching to x64 configuration   10 3s   This is 41  of acceleration

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More data is transferred between the CPU and RAM for each memory fetch  64 bits instead of 32   so 64-bit programs can be faster provided they are written so that they properly take advantage of this

[performance] Are 64 bit programs bigger and faster than 32 bit versions?

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