Recent versions of Windows, such as Windows 7 and 8, are available in both 32-bit (normal) and 64-bit versions. Once rarely used, the 64-bit versions are becoming more widespread. What advantages does 64-bit Windows offer to GEMPACK users ?
32-bit Windows will not allow any one program to use more than 2GB of memory. Very large models (such as 57-good, 100-region GTAP) require more than this. As well, 32-bit Windows can access only around 3.5GB of memory in total (even if you installed 4GB). Assuming that 0.5GB is required for system purposes, 3GB is left to share among running programs. Therefore, you could not simultaneously run 4 programs which each used 0.8GB of memory. You might think that this would be rarely needed -- however, recent versions of GEMPACK and RunDynam exploit the power of dual- or quad-core PCs via forms of parallel processing. To do this they simultaneously run several instances of model solution programs in the background. As more programs are running, more memory is needed. Of course, if you like to keep open several ViewHARs, TABmate, ViewSOL, Excel, Word, an email client and a browser, those programs also will increase your memory needs. If total memory needs approach the 3.5GB limit, the PC may become sluggish, especially when switching between programs.
64-bit Windows can access all the memory installed in your PC (we recommend 6 or 8GB). That enables you to run more programs at once, and to switch between programs without delay. The PC will seem more responsive, and may actually run faster.
Most 32-bit programs run fine under 64-bit Windows, but each one can still only use up to 2GB of memory (although see below). However, 64-bit programs can use all the memory that is available. Currently, GEMPACK-related 64-bit programs are only available to users of source-code GEMPACK who are using a 64-bit version of the Intel or GFortran compiler. Those users compile 64-bit versions of most GEMPACK command-line programs when they install GEMPACK, and they compile 64-bit versions of TABLO-generated (model-specific) programs when they run LTG. The latter is the only way to solve models (such as un-aggregated GTAP) which require more than 2GB of RAM. Note that:
As stated above, 32-bit programs can usually use only up to 2GB of memory even when running under 64-bit Windows. However, some specially-configured 32-bit programs, called 'Large-Address-Aware' are able to use up to 4GB of memory, if run under 64-bit Windows. Since GEMPACK Release 10.0-002 (around April 2010), most 32-bit program EXE files shipped with GEMPACK are Large-Address-Aware. As well, compile options are altered for source-code GEMPACK users who use the 32-bit Intel compiler so that EXE files they produce (at install time and later) will be 'Large-Address-Aware'. The effect is be to double the memory accessible (from 2 to 4GB) to these 32-bit programs if run under 64-bit Windows.
64-bit Windows is not less annoying: If you are upgrading from XP, you will notice various changes -- some of which may annoy
you. These possibly annoying features are the same whether you choose the 32-bit or the 64-bit version of Windows. On the plus side, you can enjoy
some fabulous new features.
64-bit XP is a fine, but rather old, operating system. We do not recommend it for new installs.
Your IT department may not support 64-bit Windows: you may need to wait 1 or 2 years while they catch up.
Related topics:
Large-Address-Aware (LAA) programs
Best New PC for GEMPACK?
64-bit computing and parallel computations with GEMPACK 10
Not Enough Memory to Solve a Model
Memory Limit for GEMPACK
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