(1-2 SPARC CPUs), Hs (2-4 SPARC CPUs), Ei (1 x86 CPU), Hi (2 x86 CPUs)) ranges of SPARC and Intel-based machines, running DRS/NX Unix or Microsoft Windows NT. DRS 6000 Level 200 Series DRS 6000 Level 600 Series DRS PWS In 1987, the DRS Professional Work Station (PWS) was ICL's first foray into IBM PC/AT compatible computing. The DRS PWS was initially released with MS-DOS 4.0 (not to be confused with the later public releases of IBM DOS 4.0 in July 1988 and MS-DOS 4.01 in November 1988). This was a real-mode pre-emptive multitasking version of MS-DOS 2.0 and was also the forerunner of OS/2. It was soon replaced with MS-DOS 4.1 when this became available; this was written especially for the DRS PWS, but was not finished for the launch. Microsoft agreed to write a custom version of MS-DOS 4.0 for ICL that would take advantage of the extra memory on the ICL computers. As a consequence, PWS users had a number of software compatibility challenges, although the PC Business Unit (PCBU) at ICL BRA04, in Bracknell, did patch some applications for larger customers. The PWS was positioned to compete with the IBM Personal System/2 (PS/2) and the DEC Vaxstation 2000. In 1988, the DRS PWS and DRS PWS 386 were respectively rebranded as the DRS Model 60 and DRS Model 80. The PWS hardware was a large desktop or floor standing tower chassis, running on an Intel 8 MHz 80286 processor that was later superseded by an Intel 20 MHz 80386 (DRS PWS 386). Memory expansion was via proprietary cards (1 MB or 4 MB cards, 16 MB total) and initially there was no support for 1.44 MB High Density (HD) floppy drives, although a hardware modification to the clock lines on the floppy disk controller meant that later versions of the PWS could be upgraded. The ENGA (EGA compatible video) controller, displayed standard EGA graphics and text with an additional line reserved on the bottom row for multitasking and communications task messages. The PWS was capable of communicating with ICL departmental and mainframe services using a combination of Microlan2 and OSLAN (Open Systems Local Area Network) protocols. Microsoft and OSLAN network connectivity was supported via BICC OSLAN cards (OSLAN being ICL's implementation of OSI transport protocols over Ethernet). TCP/IP and DECnet support was implemented by third parties using packet drivers, as NDIS was not available at this