The s390 is not a midrange platform: it evolved into what we call zSeries these days and is pretty much the highest end of IBM's portfolio.
5250s were terminals used with the System/34 family, which was succeeded by the AS/400 series which is now called iSeries and moved to POWER many years ago.
5250s were terminals used with the System/34 family, which was succeeded by the AS/400 series which is now called iSeries and moved to POWER many years ago.