On 11/3/24 10:06, David Wise via cctalk wrote: > 1620 owner here. > > Sure there are ways to cause a CHECK STOP, and one-instruction infinite > loops, including the IBM-sanctioned one you describe below - which everyone > used all day to clobber core - but that's all they are, they don't damage > hardware. > > You can make an infinite loop that is sort of less than one instruction. > It's an instruction with a self-referencing indirect address. (Only applies > to Model II, and Model I machines with the Indirect Addressing feature > installed, like mine.) When it tries to fetch the indirect operand, it loops > in the Fetch cycle without ever reaching Execute stage. While that sounds > like a core hammer, it is still less than 30% duty cycle on any one address. > Also remember the core stack has air blowing through it nonstop.
Sure, there was more than one way to, say, clear memory on a 1620 with a single instruction--and it was common knowledge. One could use a transmit record or transmit field instruction that not only over-wrote general memory, but also clobbered the instruction itself. Such is the glory of variable field/record length architectures. --Chuck
