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BS2000 (officially renamed BS2000/OSD in 1992) is the mainframe operating system platform of Fujitsu Siemens Computers.

Mainframe systems are optimized to enable many programs to be installed in parallel and run concurrently on a computer. This helps reduce the number of computers required to a minimum. Originally this was a way to achieve cost savings, since at that time hardware components were considerably more expensive than now. Today, the advantage of an architecture that gets by with significantly fewer computers is that it greatly reduces the complexity of the IT infrastructure, thus saving on IT running costs and increasing IT robustness.

To avoid different applications and users on a computer adversely affecting one another by contending for resources, mainframe systems must be able to segregate the different users and processes from one another in an optimum manner. They do this by virtualizing all the resources used by the applications and by centralized resource management controlled in a finely graduated way based on access rights and priorities.

At the same time the high degree of virtualization decouples the application software from hardware and implementation details and so creates the foundation for the long-term compatibility, high flexibility, high availability, extensive scalability and great robustness of the services running on mainframes.

Unlike other mainframe systems, BS2000/OSD provides exactly the same interface in all operating modes (batch, interactive and online transaction processing) and regardless of whether it is running natively or as a guest system in a virtual machine. This uniformity of the user interface and the entire BS2000 software configuration makes administration and automation particularly easy.


Looking back over the history of its development, BS2000/OSD has its roots in the TSOS operating system (TSOS: Time Sharing Operating System) first developed by RCA for the /46 model of the Spectra/70 series, a computer family of the late 1960s related in its architecture to IBM’s /360 series. It was one of the very first operating systems in which the principle of virtual addressing and a segregated address space for the programs of different users was systematically introduced. Right from the outset TSOS also allowed the data peripherals to be accessed only via record- or block-oriented file interfaces, thereby preventing the necessity to implement device dependencies in user programs.



BS2000 V1.0 – Porting of the TSOS operating system to models of the Siemens system 7.700


BS2000 V2.0 – In June 1975, Siemens shipped the enhanced version of the TSOS operating system for the models of the Siemens 7.700 mainframe series for the first time under the name BS2000. Even this first BS2000 version supported disk paging and three different operating modes in the same system: interactive dialog, batch, and transaction mode, a precursor of Online Transaction Processing (OLTP mode).


The TRANSDATA communication system marked the entry into modern computer networking.


The introduction of multiprocessor technology brought an improvement in system availability. From that moment on, the operating system had the ability to cope with a processor failure. At the same time the new technology considerably extended the performance range of the system.


A transaction processing monitor, the Universal Transaction Monitor (UTM), was introduced, providing support for online transaction processing as an additional operating mode, and one particularly important for mainframes.



BS2000 V9.0 – BS2000 is ported to the /370 architecture and now supports 2GB address spaces, 512 processes and the XS channel system (Dynamic Channel Subsystem).



With the advent of the VM2000 virtual machine, multiple BS2000 systems, of the same or different versions, can now run in parallel on the same computer. The new hierarchical storage management system HSMS automatically swaps out infrequently used data to cheaper storage media. As soon as this data is needed again, it is restored, again automatically, to high-speed access media. The Maren tape archiving system supports the connection of robot systems.


BS2000 is subdivided into subsystems that are strongly decoupled from one another. This increases flexibility for ongoing development and in shipment of software. Security evaluation to F2/Q3 completed.

1992 / 1995

BS2000/OSD V1.0 – BS2000 is realigned to make it open to application software and from then on bears the name BS2000/OSD (Open Server Dimension). Full support of the XPG4 standard is achieved in 1995 after the porting of the POSIX interfaces in 1992.


BS2000/OSD is ported to the RISC architecture. Although the operating system now runs on different hardware architectures (S servers with /390 architecture and SR2000 servers for the RISC architecture), object-compatible execution is guaranteed for BS2000 applications. Applications produced for /390 can be used on computers based on RISC architecture without recompilation.


With WebTransactions, existing BS2000 applications can be easily internet-enabled, with no need for programmer intervention in these applications.


BS2000/OSD is the first operating system worldwide to be awarded Internet Branding by The Open Group.



BS2000/OSD is ported to the SPARC architecture, leading to the creation of the new SX server line. This marks Fujitsu Siemens Computers’ consistent pursuit of its strategy of hardware independence while at the same time maintaining full compatibility.


Support for enterprise-wide storage area networks (SANs) based on Fibre Channel technology enables throughput rates to be increased by as much as 50%.


The mainframe system celebrates its 30th birthday in July.


BS2000/OSD V7.0 – Support of new server generations, Unicode support, improved SAN integration.


Release of the new BS2000/OSD version 7.0. Development highlights are: the Snap and Clone functionality of the EMC Symmetrix DMX storage systems made available for BS2000 files and disks; online provisioning for pubsets (this function automatically adds disks from a free disk pool to a BS2000 file system as needed or returns disks to this pool when they are no longer required); autonomous, dynamic control of I/O resources (IORM). Like the priority control used in the allocation of CPU timeslices, this function implements a priority control system for processes when accessing I/O resources.

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