Fixed Head area over the first five cylinders, thereby reducing seek time to zero for these five cylinders. This fixed head area is intended to be allocated to the frequently accessed HASP or JES2 checkpoint area and thus greatly reduce head motion on the SPOOL device. The fixed head area can also be utilized for TSO swap data (MVT and SVS) and system swap data (MVS) wherein the swap data for SVS and MVS consist of blocks of pages that have been in memory when an address space is selected for swap-out; those pages need not be contiguous and in general do not include pages that have not been modified since their last page-in. This system architecture greatly improves context switches between TSO users or batch regions. The IBM 3350 family was withdrawn in September 1994. IBM 3370 and 3375 IBM 3370 IBM introduced the IBM 3370 Direct Access Storage Device in January 1979 for IBM 4331, 4341, and System/38 midrange computers. It has seven fixed disks, and each unit has a capacity of 571 MB. It was the first HDD to use thin-film head technology; research on that technology started at Thomas J. Watson Research Center in the late 1960s. The 3370 was a fixed-block architecture device, used on DOS/VSE and VM, the only S/370 operating systems that supported FBA devices. IBM 3375 The sister unit was called the IBM 3375 and used count key data architecture, which was required for OS/360 and successor OSes. IBM 3380 The IBM 3380 Direct Access Storage Device was introduced in June 1980. It uses film head technology and has a unit capacity of 2.52 gigabytes (two hard disk assemblies each with two independent actuators each accessing 630 MB within one chassis) with a data transfer rate of 3 megabytes per second. Average access time was 16 ms. Purchase price at time of introduction ranged from $81,000 to $142,200. Due to tribology problems encountered between heads and media, the first units did not ship until October 1981. In February 1985 IBM announced a double density version – the Extended Capability Models of the 3380 (3380 E) having 5.04 gigabytes per chassis, that is, two 1.26 gigabyte actuators on two hard disk assemblies in one chassis. A triple capacity version, the 3380 K was announced in August 1987 having 7.562 gigabytes per chassis, that is, two 1.89 gigabyte actuators on two hard disk assemblies