Related Machines
The Amdahl 4705 was compatible with and ran about 2.5 times as fast as a comparable 3705-II. The IBM 3704 was an entry level version of the 3705. It was restricted to 26 half duplex lines (assuming Type 2 Scanner). DMA devices were not supported on the 3704. Performance was about the same as a 3705-I. A 4704 (a 3704-compatible device) was planned, but was never introduced.
The Amdahl 4745 was completely and in every respect a logical superset, or a physical subset of the IBM 3745. Whereas the IBM 3745 offered one or two physical processors, and one or two physical buses, both apparently for redundancy, the Amdahl offered one very highly reliable physical processor and one very highly reliable physical bus (but two logical buses), with no apparent need for redundancy. Whereas the IBM 3745 offered two buses, the Amdahl 4745 offered a single bus which throughput capacity exceeded the aggregate throughput capacity of the two buses of the IBM 3745.
The design of the Amdahl 4745 was such that the control program (NCP) could not tell whether it was operating in an IBM 3745 or in an Amdahl 4745 (or, for that matter, in an IBM 3725 or in an Amdahl 4725). Amdahl's logical and physical simulation of the IBM 3745 (IBM 3725) was that complete.
Later, a very high-speed scanner was offered with the Amdahl 4745 (and also with the Amdahl 4725, for which IBM had no such corresponding 3725 offering) which offered increased redundancy over the IBM 4745 very high-speed scanner (1.544 Mbit/s, T1, or 2.048 Mbit/s, E1).
Read more about this topic: IBM 3705 Communications Controller
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