Indeed, it was an important security feature. I think Bill is just saying that they should've got PC manfacturers to add a "Log On" key to the keyboard which they could've caught in the OS in the same way as Ctrl+Alt+Del.

I think the only other key that has this low-level trap feature is SysRq (usually Alt+PrintScreen), which, of course, Linux uses for [Magic SysRq](https://en.wikipedia.org/wiki/Magic_SysRq_key).

Now that I think of it, "Press 'System Request' to log on" has a nice ring to it. A shame it was it in the shifted position on IBM PC keyboards.