A debug build generates a file containing debug symbols (.pdb); a release build does not.
A debug build generates extra instructions to accomodate the debugger (e.g. NOP instructions to assist your setting breakpoints); a release build does not include these.
A release build uses full optimizations when compiling which might include rearranging your code or inlining it for efficiency, a debug build doesn't do this.
A debug build allocates extra memory on the heap for objects to facilitate detecting memory overwrite errors; a release build doesn't do this.
A release build will thus be smaller, faster, and more efficient than a debug build.
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