Complex sentence: Linux on System z is available in both 31-bit and 64-bit versions, with the 31-bit versions rapidly losing favor as z/Architecture mainframes become more prevalent than the earlier ESA/390 generation.
Split into simpler sentences: Linux on System z is available in both 31-bit and 64-bit versions. The 31-bit versions are rapidly losing favor as z/Architecture mainframes become more prevalent than the earlier ESA/390 generation.