in the microcode that allowed Digital Research to run emulation mode much faster (see LOADALL). These same limitations affected FlexOS 286 version 1.x, a reengineered derivation of Concurrent DOS 286, which was developed by Digital Research's new Flexible Automation Business Unit in Monterey, California, since 1986. Later versions added compatibility with PC DOS 2.x and 3.x. Known versions include: Concurrent DOS 286 1.0 (1985) Concurrent DOS 286 1.1 (1986-01-07) Concurrent DOS 286 1.2 (1986) FlexOS 286 1.3 (November 1986) FlexOS 286 1.31 (May 1987) Concurrent DOS XM and Concurrent DOS 386 The OEM Support Group was relocated into Digital Research's newly created European Development Centre (EDC) in Hungerford, UK in 1986, which started to take over further development of the Concurrent DOS family since Concurrent DOS 4.11, including siblings like DOS Plus and successors. Developed in Hungerford, UK, versions 5 and 6 (Concurrent DOS XM, with XM standing for Expanded Memory) could bank switch up to 8 MB of EEMS to provide a real-mode environment to run multiple CP/M-86 and DOS programs concurrently and support up to three users (one local and up to two hooked up via serial terminals). In 1987, Concurrent DOS 86 was rewritten to become Concurrent DOS 386, still a continuation of the classical XIOS & BDOS architecture. This ran on machines equipped with the Intel 80386 and later processors, using the 386's hardware facilities for virtualizing the hardware, allowing most DOS applications to run unmodified under Concurrent DOS 386, even on terminals. The OS supported concurrent multiuser file access, allowing multiuser applications to run as if they were on individual PCs attached to a network server. Concurrent DOS 386 allowed a single server to support a number of users on dumb terminals or inexpensive low-specification PCs running terminal emulation software, without the need for expensive workstations and then-expensive network cards. It was a true multiuser system; several users could use a single database with record locking to prevent mutual interference. Concurrent DOS 6.0 represented also the starting point for the DR DOS family, which was carved out of it. Known versions include: DR Concurrent PC DOS XM 5.0 (BDOS 5.0) DR Concurrent DOS XM 5.0 (BDOS 5.0, October 1986) DR Concurrent DOS XM 5.1 (BDOS 5.1?, January 1987) DR Concurrent DOS XM 5.2 (BDOS 5.2?, September 1987) DR Concurrent DOS XM 6.0 (BDOS 6.0, 1987-11-18), 6.01 (1987) DR Concurrent DOS XM 6.2 (BDOS 6.2), 6.21