Mitsubishi Electric announced the MELCOM EX900 series in April 1991 as its new mainframe series. IBM Japan supplied the OEM machines based on an agreement for mainframes. The MELCOM EX900 series advanced the features of the MELCOM EX800 series but used the same GOS/EA operating system to continue to support client software. EX900 models also came with IBM’s MVS/ESA operating system.
The EX900 series covered a 4.5-fold performance range with six upgradeable models. Up to 1 GB of main memory was supported, and the main memory could be split into main memory units and expanded memory units with IMPL. A logical partition function allowed one processor to be split into as many as seven logical processors, each running a different system. Optical-fiber serial channels were used for the I/O system, which achieved transfer speeds of 10 MB per second, a substantial improvement over the 3 MB per second of past parallel channels.
| Model | 900/190 | 900/210 | 900/260 | 900/320 | 900/440 | 900/480 | |
|---|---|---|---|---|---|---|---|
| No. of CPUs | 1 | 1 | 1 | 1 | 2 | 2 | |
| Memory capacity [MB] | 64 - 512 | 64 - 1024 | 64 - 1024 | 64 - 1024 | 128 - 1024 | 128 - 1024 | |
| Main memory [MB] | 32 - 128 | 32 - 256 | 32 - 256 | 32 - 256 | 32 - 256 | 32 - 256 | |
| Expanded memory [MB] | 0 - 480 | 0 - 992 | 0 - 992 | 0 - 992 | 0 - 992 | 0 - 992 | |
| Channels | 32 | 48 | 48 | 48 | 48 | 48 | |
| Parallel channels | 8 - 24 | 8 - 48 | 12 - 48 | 12 - 48 | 12 - 48 | 12 - 48 | |
| Serial channels | 0 - 20 | 0 - 36 | 0 - 36 | 0 - 36 | 0 - 36 | 0 - 36 | |
| Vector unit | 1 | 1 | 1 | 1 | 2 | 2 | |
