The difference is that IBM made abstractions of machines work through several generations of hardware. That abstraction has let them maintain software compatibility at a binary level for longer than any other vendor... you can literally take production programs written for and running on the System/38 and migrate them to modern iSeries systems.
IBM's methods have let them maintain compatibility despite moving the iSeries through several generations of hardware. It originally ran on their IPMI cpu, then later was migrated to the RS64, and now runs on POWER series hardware, the same as AIX (and in fact virtual instances can share chassis hardware with AIX instances).
So in fact there are services to companies still running today that originally ran on IBM's mainframes that have been migrated and migrated again, and have essentially always been up and available. The companies aren't forced to spend the money and time to plan upgrades because their previous hardware and OS isn't supported any more (contrast to Microsoft).
Lots of companies advertise upward compatibility. Some of them manage it for a single generation of hardware... after all, virtual machines are a thing. Continually migrating upward over a span of 45+ years is a technical achievement not matched by any other company.
The down side to this is that they're bound in some sense by technical decisions made long ago... so they can't modernize their software environment like e.g. Apple can.
> The difference is that IBM made abstractions of machines work through several generations of hardware
Great idea - but with PASE they’ve effectively killed it. With PASE the abstraction is gone and everything compiles to POWER machine code, which makes it no more “abstracted” than AIX or Linux or Windows is. And they keep on encouraging customers and ISVs to do more with PASE, and more of their own products rely on it. Which means IBM i is going to die on POWER, and the whole hardware abstraction stuff, while used to great effect once (the CISC-to-RISC transition), is now pointless
IBM's methods have let them maintain compatibility despite moving the iSeries through several generations of hardware. It originally ran on their IPMI cpu, then later was migrated to the RS64, and now runs on POWER series hardware, the same as AIX (and in fact virtual instances can share chassis hardware with AIX instances).
So in fact there are services to companies still running today that originally ran on IBM's mainframes that have been migrated and migrated again, and have essentially always been up and available. The companies aren't forced to spend the money and time to plan upgrades because their previous hardware and OS isn't supported any more (contrast to Microsoft).
Lots of companies advertise upward compatibility. Some of them manage it for a single generation of hardware... after all, virtual machines are a thing. Continually migrating upward over a span of 45+ years is a technical achievement not matched by any other company.
The down side to this is that they're bound in some sense by technical decisions made long ago... so they can't modernize their software environment like e.g. Apple can.