'Brookdale' Or I845
You have certainly noticed it by now; I am talking about the upcoming i845 chipset (formerly known as 'Brookdale') that stole the show of everything else at the recent Computex 2001 in Taipei. It is common knowledge by now that this chipset is also supporting DDR-SDRAM, but Intel is unwilling to release i845 plus DDR anytime soon. In August we will have the chance to build nice and clean RDRAM-free Pentium 4 systems, but instead of the obvious alternative DDR-SDRAM, we will have to use PC133 SDRAM. It is not very hard to imagine that this slightly outdated and somewhat slow memory type will have a major performance impact on Pentium 4. The question is only how much of an impediment PC133 memory will be for Pentium 4.
Let have a look at some of the facts:
| Header Cell - Column 0 | PC133 SDRAM | DDR-SDRAM | RDRAM |
|---|---|---|---|
| Introduction | Q2/1999(VIA-chipset) | Q3/2000(AMD-chipset) | Q3/1999(Intel-chipset) |
| Price | very low | very low to low | mid to high |
| Production/Sales | Very high | mid-high | low |
| Bandwidth(one channel) | 1 GB/s | 1.6 - 2 GB/s | 1.6 GB/s |
| Chipsets | Numerous VIA, Intel i815, SiS | AMD760, numerous VIA, ALi, SiS | Intel i820 |
| Bandwidth(two channels) | 2 GB/s | 3.2 - 4.1 GB/s | 3.2 GB/s |
| Chipsets | ALi | NVIDIA nForce420 | Intel i840, i850, i860 |
| Memory Latency | low | low | high |
| Performance with Processors: | Row 8 - Cell 1 | Row 8 - Cell 2 | Row 8 - Cell 3 |
| AMD Athlon/Duron | mid | high | n/a |
| Intel Pentium III | mid | mid | Low-mid |
| Pentium 4 | low | n/a | High (?) |
The table shows that PC133 is the oldest of the three currently available memory types on the market. It comes with the lowest bandwidth, though with the lowest (and thus best) latency as well. PC133 is very inexpensive, but the price advantage over the more advanced DDR-SDRAM is shrinking daily and does not play a major role in cost considerations anymore.
One-channel SDRAM configurations, such as in case of the upcoming i845, can only provide a third of the bandwidth of current Pentium 4 platforms with i850 chipset. From that point of view it seems very likely that i845 will starve Pentium 4 for data. However, we know from Pentium III systems that PC133 is able to outperform RDRAM if the bandwidth doesn't come into play, because RDRAM's latency is so much higher than that of PC133 SDRAM that the PC133 i815 platform is able to outperform the RDRAM chipsets i820 and i840.
