25 Jul
2014
25 Jul
'14
3:56 a.m.
On 7/25/2014 12:04 AM, Paul Birkel wrote:
On Thu, Jul 24, 2014 at 10:22 PM, Eric Smith
<spacewar at gmail.com> wrote:
As far as I know they still have a patch capability, but I think the
processors run pretty well before they leave the fold now days. There is
a capability to load and install signed blocks of updates that are added
to bios which support some processors. These are dumped into the
processor and are encrypted so that the bios manufacturers have little
to no way to know what they contain. The processor unpacks and does
with them as need be after the bios dumps them in (or as they do, don't
know the mechanism fully).
The mechanism in the Pentium was almost open compared to what is there
now. All of this is under heavy NDA as far as it even being there, and
it may or may not be these days.
...
The VAX-11/780 introduced the concept of patchable control store,
where most of the control store was PROM but there was a small amount
of patch RAM. Costs of high speed RAM declined quickly enough that
most later non-microprocessor VAXen used entirely RAM control store.
With the advent of VAX microprocessors, the larger die area required
for RAM vs ROM shifted the economics shifted back to favor ROM with a
small RAM patch area.
Intel started supporting a RAM patch area, I believe, after the Pentium bug
so that they could field-update during the low-level boot process to
(quietly!) overcome any similar problem in the future. Does anyone have
more specifics on this feature, and does this capability currently exist in
any of their more modern CPU architectures?
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paul