A storage-hierarchy system for batch processing

Operating System/360 was designed to meet a severe core-memory constraint: a 14K-bytes resident supervisor plus a repertoire of compilers, utility programs, sort programs, and application packages fitting into 18K bytes (approximately 4500 data words and executable instructions). Many supervisory functions included in the nucleus of pre-360 systems were repackaged into 1000-byte overlays for OS/360 (e.g. logic to OPEN and CLOSE files---hereafter called data sets, following OS/360 nomenclature). Specification of device type, buffering technique, and data set identification---which was assembled, compiled, or link-edited into many pre-360 application programs --- is deferrable in OS/360 until the data set is actually opened for processing, essentially "latest-possible binding of data-set attributes and processing mode" (cf. Part 3 of Reference 5 for a complete discussion).