The decompiler requires the latest version of IDA. While it may work with older versions (we try to ensure compatibility with a couple of previous versions), the best results are obtained with the latest version: first, IDA analyses files better; second, the decompiler can use additional available functionality.
The decompiler runs on MS Windows, Linux, and Mac OS X. It can decompile programs for other operating systems, provided they have been built using GCC/Clang/Visual Studio/Borland compilers.
32-bit decompilers require the 32-bit version of IDA to run (IDA Starter is enough).
64-bit decompilers require the 64-bit version of IDA to run (IDA Pro is required).
IDA loads appropriate decompilers depending on the input file. If it cannot find any decompiler for the current input file, no decompilers will be loaded at all.