IBM System/32 available

Eric Smith spacewar at
Tue Nov 10 00:54:06 CST 2015

On Mon, Nov 9, 2015 at 9:25 PM, Guy Sotomayor <ggs at> wrote:
> The 8259 (along with the damned 8254) are still alive and well in current
> Intel PCHs.

As I said, it's still there for compatibility. However AFAIK most OSes
use the APIC instead, at least by default. Linux has a kernel command
line option that can be used to ignore the APIC and use the 8259As.

If you want true SMP for multiple cores, you have to use the APIC, as
the 8259A doesn't support that.

> Actually as of Windows 8.x the 8254 is *still* used.  :-(

Windows 8 and later use the LAPIC timer (in the APIC) as well.

Linux if configured for a tickless kernel uses the LAPIC and does not
use the 8254.

Windows XP recognized but did not use the HPET timer, which present in
most recent CPUs or bridges, and was intended as an improved
replacement for the 8254.

Linux normally uses the TSC as its timebase, but Wikipedia says that
Linux can use the HPET as a fallback.

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