Examination I
We've already covered the basic architectural analysis of the Athlon 64 3200+, although it wasn't published in a discrete review. To help the uninitiated grasp the merits of the 3400+ model, we'll seek to outline its finer qualities that help distinguish it from the Barton series.Integrated memory controller
A portion of the 3400+'s die is reserved for an on-chip memory controller. The memory controller interfaces with system RAM through a DRAM controller, which can be modified as new memory standards emerge. An integrated memory controller, it is reckoned, can reduce latency penalties by up to 25%, and takes away the need for chipset makers to get an efficient memory controller right the first time around; AMD has done the hard part for them. As the memory controller runs at full core speed, the DRAM controller is a divisor of the CPU's speed, such that traditional PC1600, 2100, 2700 and 3200 speeds are catered for. Chipsets still adhere to the PC3200 standard, so we don't expect native support for PC4000 memory immediately.
The way that system memory interacts with the CPU is different from the Barton. As the memory is running at a division of CPU speed, it cannot always be guaranteed to hit certain JEDEC-approved speeds. For instance, with the 3400+ running at 2.2GHz, requesting PC2700 compliance gives rise to a DRAM divisor of /14 (2200MHz / 14 = 157.14MHz, DDR314.28). That's why users often see a 'memory limit' function on S754 motherboards. In effect, the divisors ensure that memory specifications aren't breached.
The obvious difference from this and the FX-51 CPU, whilst both run at 2.2GHz, is the lack of ECC support (which is a good thing from a performance point of view) and a single-channel memory architecture. We'd normally slate the lack of bandwidth, a possible 3.2GB/s at 200MHz in this case, as an obvious performance inhibitor. However, our S754 motherboard reviews have shown that, if setup correctly with low latencies, the 3200+ has been a formidable performer. There's no reason to suspect that isn't the case with the nominally faster 3400+ model.
Larger L2 cache
The 3400+ is an expensive CPU to produce. There's not much AMD can do about that. Its die is almost twice as large as the Barton's 101mm² and comfortably more than twice as large as the Thoroughbred's 84mm². Consider the transistor-heavy Pentium 4 Extreme Edition for a moment. A large die size and overall transistor count is usually indicative of a larger on-chip cache. The 3400+ uses 1024kb of L2 cache - the part of the chip which can store quickly needed information. CPUs use intelligent pre-fetching of data to load up on on-chip cache. Having more CPU cache is better, and 1MB provides tangible performance gains over the Barton's 512kb.
Silicon-On-Insulator Technology.
Silicon-On-Insulator (SOI) is exactly like it sounds. A layer of silicon dioxide sits in between the transistor(s) and substrate. The advantage is in ensuring that fewer electrons can escape to the wafer underneath. It also reduces the thermal requirements for operation at a certain MHz. The Athlon 64 is all about efficiency, and SOI technology embodies that principle. It's one of the reasons that AMD feels confident in releasing a faster S754 CPU before the year is out.
HyperTransport links
With the CPU using an integrated memory controller, its link to the motherboard's chipset isn't necessarily the usual CPU-to-Northbridge route that we've become accustomed to. Rather, it interacts with a 16-bit-wide 800MHz HyperTransport bus. That's up to 3.2GB/s in each direction, and NVIDIA's nForce3 150, with its single-bridge design, is in the best position to take advantage of this high-speed link. The vagaries of the chipset, however, make it a less than ideal partner.
Other features
Then there's other desirably traits, such as SSE2 support, AMD64's ISA, larger L2 TLBs (Translation lookaside buffers, 0.13-micron production, and Cool'n'Quiet technology.. Readers may be under the impression that the Athlon 64, then, is a totally new CPU. That's not the case, especially with respect to 32-bit code. The K7 (Barton 3200+) and K8 (Athlon 64 3400+) share a surprising degree of similarity in the way operations are carried out. AMD has just refined the process
