Features in Detail Continued
- The Die; it may be small but its big where it counts
Intel's Pentium 4 Willamette is available in two packages; Socket 423 and Socket 478, while the Northwood is 478 only. While the 478-pin Pentium 4 may sound like it would be a larger CPU, it is actually smaller; about 1/3 the size of a 423 Pentium 4. mPGA pins are about the size of a pin head and spaced less than 1mm apart. Willamette was built on the same core process as the Coppermine P3 and Celeron CPUs; a 0.18 micron die. Intel has dropped the core size to that of the new Celeron Tualatin core; 0.13 micron. While the physical features of the Northwood are identical to the Willamette, under the heat spreader lies a tiny die consuming only 1.4 to 1.5v rather than the 1.7v that the Willamette core used. This has allowed greater clock speeds for current and future processors.
- Hyper-Threading Technology - 1 = 2
Hyper-Threading technology makes a single "physical" processor appear as two "Logical" processors under a Multi-processor operating system. To do this, there is one copy of the architecture state for each "logical" processor, and the "logical" processors share a single set of "physical" execution sources. In short this means that there are two architecture storage mediums but one actual layer of CPU. From a software perspective, this means operating systems and user programs can schedule processes or threads as they are known as, to each logical processor as they would on conventional physical processors, in short, the multi CPU OS's are none the wiser that there is actually only one single CPU.
Each logical processor maintains a complete set of architecture state. This architecture state consists of registers, including the general-purpose registers, the control registers, the advanced programmable interrupt controller (commonly known as APIC, yes that setting in the BIOS of some motherboards) and some machine state registers. From the software's point of view, once the architecture state is duplicated, the OS and other programs see 2 separate processors.
This implementation of Hyper-Threading technology only added around 5% to the die size of the already small Intel Pentium 4 CPU. Since the die itself is covered by the Integrated Heat Spreader (HIS) you will see no actual changes in the chip itself as compared to usual.