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Untitled Document
Chipsets
There are currently three main chipset families on the market.
- nVidia nForce 3
- VIA K8T800
- SiS 755
The simplest chipset to correctly identify is the SiS 755. There are no fancy
variants of this chipset at all, just the plain vanilla model.
The VIA K8T800 is also fairly simple. The Pro version gives the added benefits
of lockable AGP and PCI Buses, support for 1000MHz HyperTransport and twice
the bandwidth between the north bridge and south bridge, increasing the overall
bandwidth available to the NIC, PCI slots, and IDE interfaces.
The nForce family is divided into two generations, the 150 and the 250. The
150 has a slower HyperTransport implementation and lacks the ability to lock
the AGP and PCI buses. The 250s have AGP and PCI locks, a standard 800MHz HyperTransport
implementation and updated SATA support, with some tweaks to the onboard audio
as well. The GB versions are exactly the same, but include Gigabit Ethernet
support (including their firewall solution). nVidia don't use a separate north/south
bridge like VIA and SiS, but instead a single chip. This helps reduce latency
and will give faster hard disk performance. The Gigabit NIC is also superior
becuase it does not go through the PCI bus and can therefore acheive much closer
to true Gigabit speeds.
Before comparing the chipsets performance against each other, it is worth seeing
what factors have the most impact on Athlon 64 performance, and why.
Frequencies and Ratios
On an Athlon 64 platform, the FSB only means the speed at which the north bridge
core runs. The HyperTransport bus runs at FSB times a certain ratio. On many
boards, this ratio can be changed. As usual, the CPU runs at a ratio of the
FSB speed, as do the AGP and PCI buses. This means that the HyperTransport Bus
can be changed independently of the North Bridge and CPU speeds by simply adjusting
the ratio.
The HyperTransport speeds are the first major difference to be found between
the various chipsets.
| Chipset |
Speed (UpStream) |
Width (UpStream) |
Speed (DownStream) |
Width (DownStream) |
| nForce 3 150 |
600 MHz |
8-Bit |
600 MHz |
16-Bit |
| nForce 3 250 |
800 MHz |
16-Bit |
800 MHz |
16-Bit |
| K8T800 |
800 MHz |
16-Bit |
800 MHz |
16-Bit |
| K8T800 Pro |
1000 MHz |
16-Bit |
1000 MHz |
16-Bit |
| SiS 755 |
800 MHz |
16-Bit |
800 MHz |
16-Bit |
Bandwidth can be calculated using width x frequency. Using this, we can see
that a 600MHz 8-Bit solution has the same bandwidth as that of a 300MHz 16-Bit
solution, making nVidias solution quite crippled on the bandwidth front. The
question is, what difference does this make?
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