The PM133 southbridge is VIA's model VT82C686A. The southbridge is not as modern as the northbridge, and while it has a strong feature set, it is not as complete as Intel's or SiS' finest. We trimmed the list to cover just the important features:
- PCI to ISA Bridge
- Two UltraDMA/66 channels
- USB Controller with root hub and four function ports
- Integrated Super IO Controller
- Legacy keyboard and PS/2 mouse support
- AC97 audio with standard v1.0 or v2.0 AC97 Codec interface (our test board has 6-channel output)
- Five positive voltage (one internal), three temperature (one internal) and two fan-speed monitoring
- Automatic clock throttling with integrated temperature sensing
- Internal core VCC voltage sensing
- System Management Bus interface
The VT82C686A is not VIA's greatest southbridge, but it is the standard for the PM133 and it came on our test motherboard. With only a single USB controller and ATA/66 support, the southbridge makes the PM133 more of an i815 equivalent than an i815E equivalent. It is essentially last generation's chipset, which isn't bad, but won't satisfy high-end users, though tweakers will appreciate the hardware monitoring.
All normal legacy forms of I/O are supported, as well as SMBus and power saving modes, which gives the PM133 chipset enough flexibility to work in mobile applications. VIA will also be releasing a mobile-specific version of the PM133 chipset, which should use less power.
Now let's see how fast the PM133 chipset is...