The big question is, why won't 64 bit catch on? I suppose the obvious response is “Why should it?” It makes a lot of sense to have a 64-bit operating system i

The big question is, why won't 64 bit catch on? I suppose the obvious response is “Why should it?” It makes a lot of sense to have a 64-bit operating system if we have, for example, more than 4GB of memory to work with. However, unless a single process needs access to the same scale of resources all on its own, there isn’t necessarily any advantage to writing things like application code the same way. Moreover, moving to 64-bit pointers means more memory is required for data structures and for assembly level instructions that use indirection. In both cases, there is the potential for a significant performance hit, for example if less information fits into a cache. OK, what about using 64-bit instructions that let us calculate with larger values? Again, that might be useful in some contexts, but on PC processors we’ve had specialist instructions for things like double-precision floating point calculations or operating over multiple bundled values simultaneously for a long time, so there are only limited benefits to be had. Of course, set against all of these ambiguous benefits is the fact that porting to 64-bit can take a lot of work if the original code, data structures, file formats and so on were not designed with portability in mind. And once you’ve ported, if you’re also running a 32-bit version, now you have more testing to do, any related software might have to speak two protocols/APIs to remain compatible with both, etc. (This seems to be one of the main underlying points in the cited article.) Looking at the astronomical memory requirements for something like browsers opening multiple tabs these days, perhaps in the case of Firefox there really is an argument for supporting more than 4GB of RAM. On the other hand, even modern web pages full of large images and multimedia wizardry usually only come in at ~100kB or maybe ~1MB, so even with dozens of tabs open, you need to be doing an awful lot behind the scenes to be in any danger of hitting a 4GB limit. Presumably the Mozilla folks don’t expect this to be a problem.