Intel has been trying to up the performance of their Pentium 4 processors by quietly introducing new processors such as the 560 and 570J. Unfortunately these processors often offered no more than a bump in clock speed and performance increases that could only be found with a magnifying glass
. Add to that a new chipset, the 925XE, that only truly delivered on paper
and you know why AMD has been leading in terms of performance and features for the past year or so. Now that AMD has successfully been using the No eXecute bit feature, Cool ‘n Quiet and 64-bit compatibility of their processors as a sales pitch, Intel couldn’t stay behind. So what do these 600 series Pentium 4 processors offer? Are we looking at another speed bump with a few extra features thrown in, much like the Pentium 4 570J?
TM1 throttling as found on older Pentium 4 processors such as the Pentium 4 560
Well, yes and no, we’re still talking about a Pentium processor based on the Prescott core, which is notorious for its heat production and power consumption. If Intel wanted to do away with the fiery image of its Socket-775 processors they needed something similar to AMD’s Cool ‘n Quiet to keep things from running hot. Not surprisingly they adopted the same principles using in their mobile processors, the 90nm Pentium-M based on the Dothan core, on their desktop parts. The result? A Pentium 4 Prescott processor with SpeedStep, which will throttle the clock speed by changing the multiplier of the processor on the fly. We already saw a earlier version of this on the 570J, which basically put the processor in halt when the temperature went up too quickly, thereby reducing the effective clock speed, but the 600 series has a few extra tricks up its sleeve.
TM2 throttling as found on the new 600 series Pentium 4 processors
The first mechanism used is the C1E enhanced halt state, which throttles the processor down to its lowest multiplier when the load on the processor is reduced. This is much like the C1 halt state which is used on all modern processors and is triggered when the operating system's idle process issues a HLT command, for example Windows XP does this constantly when not under full load. This HLT command puts the processor in an idle state where is consumes less power and thus produces less heat. The second mechanism is the Enhanced SpeedStep which works similar to the C1E enhanced halt state but is triggered through ACPI; it dynamically adjusts both clock speed and processor core voltage and as such is more granular than the previous.
The third mechanism and one that we’ll scrutinize in this review is thermal throttling which obviously means that clock speed throttling is engaged by the processor reaching certain threshold temperatures. Pentium 4 processors have had thermal throttling since their introduction, designated by TM1 throttling, which effectively cuts active processor clock cycles in half, thus reducing load and heat production. The 600 series however introduces a new sort of thermal throttling, called TM2 throttling. TM2 throttling steps down processor clock speed and voltage via the same mechanism as C1E and SpeedStep, effectively lowering the processor’s heat production by roughly 40% without affecting performance as severely as TM1 throttling does.