The Alto could emulate different instruction sets via microcode (like their previous machine emulated a PDP-10) and it came with a built in emulation for the Da

The Alto could emulate different instruction sets via microcode (like their previous machine emulated a PDP-10) and it came with a built in emulation for the Data General Nova, but internally it was a very different machine. The biggest similarity was that it used the same ALU chip, the 74181. The article mentions that "Kay gambled his budget on Lampson and Thacker’s proposal, calling it the “Interim Dynabook.”" and this budget was for Kay's group to buy more Novas and add a frame buffer to them and high resolution displays like they already had been doing. Smalltalk-72 initially ran on one of these modified Novas. With the default emulation the Alto ran all this old code right away. Later on the Alto's flexibility allowed them to do things the Novas couldn't, like implement BitBLT and run Smalltalk or Mesa bytecodes directly. So they were not only a bridge to the past, but to the future as well. Some people who wanted an Alto but couldn't get it made their own: https://en.wikipedia.org/wiki/PERQ https://en.wikipedia.org/wiki/PERQ https://en.wikipedia.org/wiki/Lilith_(computer) https://en.wikipedia.org/wiki/Lilith_(computer)