Type 4 Channel Adapters were designed for 270x emulation. They recognized up to 256 channel addresses and transferred data in small bursts (four bytes for the Type 1; 32 bytes maximum for the Type 4). The hardware could accept almost all of the 240 possible channel command codes. Software had to analyse the command from the channel and either reject the command or process it according to specific rules. Interrupt processing required about fifty storage cycles to process a four byte transfer. The 3705 could only have a single Type 1 Adapter but two Type 4 Adapters were permitted. An Amdahl 4705 could have four Type 4 channel adapters (Type 1 channel adapters were not offered). Type 2 and Type 3 Channel Adapters were designed for NCP use only. Only one device address was recognized. Data transfer was via cycle steal which made the overhead low if large buffers were used. The hardware accepted seven channel commands of which four were completely processed by the adapter. This left a read and two write commands for the software to process. These adapters could be connected to any of the three System/370 channel types but a block multiplexor channel was preferred. The Type 3 Adapter could be simultaneously operational (but not in mid-command) on two different channels which might be connected to different hosts. An Amdahl 4705 could have Type 2 channel adapters as well as Type 4 channel adapters (up to a total of four channel adapters). Amdahl's 4705 Type 2 channel adapter also simulated a Type 3 channel adapter. 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