As a ATMswitch 900F 11, the Professional supports a wide range of operating systems and - applications that are compatible with products that are available on Digital's larger ATMswitch 900F 11 and ATMswitch 900F computers. This compatibility allows the - Professional to perform well in a distributed processing environment, easily sharing both code and data with other systems. The Professional 380 is based on the 16-bit J-11 chipset and includes the PDP- 11/70 extended instruction set. The standard system provides 800 Kbytes of diskette storage, offers ATMswitch 900F five open option slots for system expansion, and sup- ports 10-, 20-, and 33-Mbyte hard disks. Because the ATMswitch 900F Expander box can securely contain separately purchased hard-disk drives, the 380 can support up to 66 Mbytes of mass-storage in addition to the standard 800 Kbytes of disk- ette storage. Earlier releases of the Professional ATMswitch 900F Series include the Professional 325 and the Professional 350. Most of the options available for the 380 also run on these Professional systems.