Due to split power planes,
the IMC can be clocked down independently of the CPU cores, along with reduced
voltage. This also enables CPU overclocking without touching the memory
frequency, something that may appeal to enthusiasts. These features are again
dependent on Socket AM2+ and F+ platforms.
Amato explained how the
quad-core design benefits from the internal crossbar switch the backbone of
communication inside the K10 CPU. With Intel's current quad-core design there
are cases where data needs to travel over the FSB -- in AMDs case all inter-CPU
communication takes place on-die.
The crossbar switch of the
K10 core is already prepared for up to 8 cores, Amato boasted. Amato wouldn't
give even a vague timeframe for market availability of such a CPU, though he
indicated the company is prepared for whatever the market demands. Amato made
clear that octo-core is far away in the future – Shanghai will not get 8
K10 will introduce a shared
L3 cache while the individual cores have dedicated L1 and L2 caches. As long as
requested data lies in L1, it can be directly loaded. This also works if the
data lies in the L1 cache of another core, in which case the communication
works via the crossbar switch. In case requested data resides in the L2 cache,
it will be loaded to L1 and then invalidated in L2 as AMD has an exclusive
cache design. The L3 Cache, however, is not exclusive, but allows for a shared
bit to be set. If a core loads data marked as shared, it will reside in the L3
cache and can be fetched by other cores as well.
Amato also mentioned an
array of power saving measures which, in sum, allow AMD to deliver a quad-core
CPU in the same thermal envelope as today’s dual-core CPUs.
K10 adds the capability of
independently clocking all the CPU cores. In current K8 processors (and Intel's
Core 2 generation), all cores are clocked at the same level all the time -- the
P-state can only be changed synchronously. In case of a compute-intensive
single-threaded process, all cores must run on the highest level P-state. On
K10-based CPUs, the idle cores could be switched to the lowest P-state, while
others are in different states, depending on load.
This feature could possibly
be abused by overclockers to overclock a single core above the specified
levels. Amato clarified that AMD doesn't endorse overclocking, but acknowledges
there are people interested in that. In a warranty case, AMD could detect PLL
programmings out of spec which would deny the warranty. The new cores, however,
have new thermal sensors, to improve overheating protection.
Amato closed the session by
mentioning Shanghai as a successor to Barcelona in the server
space for 2008. Shanghai will be an improved quad-core architecture,
which is supposed to be socket-compatible with current Socket F platforms.
Roadmaps available to DailyTech revealed Shanghai is a 45nm
quad-core CPU featuring 6MB of L3 Cache.