Monday Platform Trends: The Intel 64-Bit Desktop

(Update -- You can read Vince Freeman's hands-on benchmark test results and under-the-hood analysis of the Pentium 4 660 and 3.73GHz Extreme Edition at our sister site Sharky Extreme here -- Ed.)

Tweaking the Core and Turning On Features

Intel likes to pretend it doesn't even pay attention to what the upstart AMD is doing, but once the latter launched its Athlon 64 offensive, Intel's Situation Room went to red alert. The 64-bit computing bug had hit the desktop market, and Intel had to do something.

A "What, me worry?" Alfred E. Neuman response, coupled with casual derision of AMD64 technology compared to Intel's enterprise-leviathan IA64, failed to impress consumers. The availability of an AMD64 Windows XP preview beta only fanned the flames of discontent. As has occurred time and again with new computer hardware, it wasn't really a case of what 64 bits could do for you today, but fear of what not having it could cost you tomorrow. So Intel finally announced its own plans for a 64-bit x86 desktop, which have just come to fruition with five new Pentium 4 processors.

EM64T Explained

The new CPUs feature what Intel calls EM64T -- Extended Memory 64 Technology, the chip giant's answer to the limitations of the venerable IA32 architecture. It starts by physically extending past the 4GB memory-addressing limit of 32-bit systems, stretching to 1 terabyte of physical and far higher capacities for virtual memory.

The 4GB ceiling may have you thinking "it's all you'll ever need" thoughts, as Bill Gates famously did for 640K, but many current high-end systems already feature 1GB and 2GB configurations and workstations can utilize 4GB with ease. Pushing these to 8GB and 16GB is a natural progression, and Intel needs EM64T in order to match AMD in physical memory addressing.

The software side is a bit more difficult to get a handle on, but it's obvious that Intel's proprietary Itanium/IA64 format is now on the back burner for all systems except enterprise servers. As an extension of the familiar 32-bit x86 instruction set, EM64T supports both existing 32-bit and new 64-bit code. This means Intel can now compete with AMD on an equal plane, making use of both 32- and 64-bit operating systems and programs, while letting AMD do all the legwork.

A virtual clone of AMD64 architecture, EM64T offers the same three operating modes: a standard 32-bit legacy mode, a compatibility mode for running 32-bit programs under a 64-bit OS, and a full 64-bit mode for both operating systems and applications. Again, this makes Intel's Itanium software base irrelevant, and leaves the company with two totally different 64-bit strategies for the enterprise and other markets.

The Prescott 2M Core

The new Pentium 4 CPUs feature a 90-nanometer-process core revision with a larger Level 2 cache and other enhancements as well as EM64T support. The on-chip L2 cache has been doubled to 2MB, which should help alleviate issues with the Prescott's long pipeline and speed memory accesses while lowering latencies.

This compares quite well to the P4 Northwood (512K L2) and Prescott (1MB L2) models, but the old-school Pentium 4 Extreme Editions are still the king of cache: Those bad boys sport both 512K of Level 2 and 2MB of Level 3 cache, and clock for clock can still outperform the Prescott 2M.

The most significant other change in the new core is the desktop debut of Enhanced Intel SpeedStep Technology (EIST) thermal and power management, similar to what's found with Intel's Centrino/Pentium M mobile technology. This feature ramps down CPU clock speeds and core voltages when the system is shy of peak processing demand, thereby cutting heat output and power usage, then scales back up to full power when usage increases.

This is an extremely important ability for any processor, but with the higher transistor count (due to the 2MB L2 cache) and greater clock speeds of the Prescott 2M, SpeedStep is imperative. Of course, this type of feature always brings calls of inadvertent "throttling down" from the performance crowd, and Intel needs to have all the kinks worked out.

For Pentium 4 desktop processors with EM64T support, the number of general-purpose registers has also been increased, and the Execute Disable (XD bit) technology already seen in Intel's "J" series CPUs -- enhanced virus protection that stops virus or worm code from propagating via data areas of system memory -- switched on. The latter matches what AMD calls NX bit technology, but there's one feature you won't find in an AMD chip: Hyper-Threading is again a default feature in both 32-and 64-bit modes, as Intel continues to tout this technology before making the move to full-fledged, dual-core processor designs.

The Pentium 4 6xx and Extreme Edition Processors

Once again, Intel has separated the new Pentium 4s into standard and Extreme Edition lines. The former includes the Pentium 4 models 660 (3.6GHz), 650 (3.4GHz), 640 (3.2GHz), and 630 (3.0GHz). These all run on the 800MHz front-side bus and use the LGA775 processor package.

The only strange thing about this release is that we already have 1MB-L2-cache, 32-bit-only Prescott models running at these clock speeds, along with the 3.8GHz Pentium 4 570J. Certainly the extra cache and EM64T are big considerations, but continually revising the core while maintaining core speeds could get real old real fast.

The new 3.73GHz Pentium 4 Extreme Edition represents a new clock-speed record for Intel's enthusiast line, but also makes some architectural changes: While the older 0.13-micron-process Extreme Edition processors were based on a Xeon core with 512K of L2 and 2MB of L3 cache, the new EE has the same 2MB of L2 and EM64T support as the Pentium 4 6xx chips, as well as the same transistor count. Aside from the extra 130MHz of clock speed, the only difference is that the Extreme Edition runs on a 1066MHz instead of the standard 800MHz front-side bus.

The Merry-Go-Round Continues

This latest Intel release is certainly good news on some ends, and the higher clock speeds and 2MB cache will come in handy at the top end of the scale. EM64T support makes sense for the future, the SpeedStep technology is a good move for the hot-running Prescott core, and overall performance does increase slightly.

What's bothersome is the feeling of deja vu, or realizing it wasn't that long ago when Intel released the first 3.6GHz Pentium 4, and it's an even shorter break since the Pentium 4/3.8 arrived. Unless the switch to 64-bit operating systems and dual-core-optimized software happens a lot more quickly than anticipated, at some point Intel will have to let the horse out of the barn and wow us with performance increases as well as feature refinements.