|
George 3 is the Operating System designed for large (and medium) ICL 1900 mainframes and takes over many of the organisational tasks previously performed by human operators. In particular once a job is input to the system it is controlled by George 3 in response to commands supplied by the user without any operator action being required. Both offline (Batch) and online (MOP - Multiple Online Programming) services are available, each mode of access offering a complete range of user facilities embracing program running and file manipulation. Jobs are not necessarily run in the order in which they are input to the system but are stored in a jobwell until the HLS (High Level Scheduler - a system program that is always active) decides to run them. The HLS decides which job to run next on the basis of scheduling data supplied by the user and machine resources available. Should a system break occur then any jobs waiting in the jobwell will be automatically preserved and any jobs running at the time of such a break will be rerun automatically when the system is re-instated. The Backing Store (Filestore) of the machine is also controlled by George 3, together with an automated backup system (Dumper). A user may store information in files in the 'Filestore' by use of suitable George commands. The user refers to these files by a name that he chooses and does not need to know anything about particular backing store devices. The size of the Filestore is not dependant on the disc storage allocated to it, this provides the 'online' Filestore. As long as sufficient safe copies of a file are held by Dumper, it can be removed from the 'online' Filestore and is then said to be 'offline'. The user has to do nothing when the file is required, it will be automatically retrieved when an attempt is made to use it. To speed jobs up, a list of files required can be specified at the beginning of a job (or as a separate preceeding job) requesting that the required files be brought back 'online' (Retrieved). In addition to the Filestore, George 3 incorporates a Tape Librarian and allows the use of disc 'exofiles' on disc packs other than the George system disc packs. Under George 3, basic peripherals (card reader/punch, paper tape reader/punch and line printers) are rarely used online, the input and output being off-lined via the Filestore. It is also possible to simulate small magnetic tape and disc files within the Filestore to avoid using real tapes and discs for small amounts of data, especially for program testing. George 3 provides facilities for Budgetting and Accounting, to both control the use of and to charge for resources. The George 4 Operating System was identical to George 3 apart from differences required to run on the paged memory machines (1906A & 1906S). There was a common source code which was conditionally compiled. Thanks to the work of David Holdsworth and Delwyn Holroyd, who obtained copies of the ICL issue tapes, backup tapes and documentation from the last live UK George 3 site while it was being decommissioned, a working copy of George 3 has been preserved. They have written a George 3 Executive Emulator (currently in beta testing) which provides an environment in which George 3 Mk 8.67 can be run under Windows 32-bit (W95 upwards) systems. It has also been run under the EWG3 Executive on the 1904S emulator (currently in development). See ICL 1900 Preservation for more details. |