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JetBrains Runtime is bundled with latest versions of all JetBrains IDEs, and is used by default, unless explicit reconfiguration was performed. The exception is 32-bit Linux systems, where IDEs require a separate JDK installation, because only 64-bit JetBrains Runtime is currently bundled. For Windows, 32-bit JetBrains Runtime is bundled, it will work on both 32-bit and 64-bit systems.
Versions of JetBrains Runtime for all supported architectures (including 32-bit Linux and 64-bit Windows systems) can be accessed via
JBR11 moved to https://github.com/JetBrains/JetBrainsRuntime#releasesJBR17 https://github.com/JetBrains/JetBrainsRuntime/tree/master17#releases
This page has instructions on changing runtime version IDEs run under. Runtime version in use can be verified in IDE's About screen.
UPDATE Starting from 2017.1 version, 64-bit runtime is bundled on all platforms by default.