System360 Hardwired vs. Microcoded 392

Eric Smith

You may well be right. As the owner of the Retrocomputing site, you would know more about these things than I would, although there are people out there who know more than both of us.

I noted, in another thread, that the Model 75 was pretty conventional as a computer; according to one book describing it innards, it got by with a 64-bit adder, another 8-bit adder for exponents, and an 8-bit BCD adder for decimal instructions (apparently also usable in binary for string compares).

But I find that the PDP-10, another conventional computer in that sense, had a performance much smaller than that of a 360-75, one comparable with the 360-50. Thus, the Model 75 obviously had something going for it. The same source shows the 360-44 slightly outperforming the 360-75; but it shows the 360-65 outperforming them both, so it may not be entirely accurate. (It attempts to normalize MIPS figures across performance measures over time so as to be able to compare everything from the Harvard Mark I to the NEC Earth Simulator; this is a difficult task, and so some inaccuracies come with the territory.)

Clearly, the Model 44 was designed in response to compebreastive pressures. And giving it the option of running the commercial instruction set was avoided, to prevent it from eating into sales of the rest of IBM's product line. Just how they did that - well, as I noted, Pugh, Johnson, and Palmer apparently doesn't even *mention* the 360-44.

John Savard