The RD2 Pro Features

The sampling or refresh rate of RD2 Pro is about 0.5 seconds. That's pretty fast but not fast enough IMHO. In Port 80/84H mode, the BIOS tests are done in a split-second. With a 0.5 second duration between each reading, the RD2 Pro will actually miss all the debug codes except the most 'recent' one. The same thing applies to the Utilization and Transfer modes.

Frequency Mode

The default speed for the PCI bus is 33.3MHz. All PCI devices are designed to run at that speed. But when you overclock the Front Side Bus (FSB), the PCI bus speed will usually be overclocked as well. This applies to most older motherboard, including all motherboard based on VIA chipsets.

Why is determining the exact PCI bus speed important? Well, some PCI devices are extremely sensitive towards any bus speed changes, like most SCSI cards. In this case, monitoring the exact PCI speed allows you to pin-point the maximum stable PCI speed for sensitive PCI devices.

Some motherboards also do not run at the standard 33.3MHz PCI bus speed because some motherboard manufacturers slightly overclock the Front Side Bus (FSB) to gain some performance advantage. Hardware reviewers will find this mode extremely useful in confirming if the motherboard manufacturer has been naughty... :)

Of all the modes, the Frequency Mode is the most useful mode for overclockers. This is because the PCI bus speed is usually the limiting factor whenever someone overclocks. With this mode, the overclocker can determine exactly what his system's maximum stable PCI clock speed is.

There is a 'Multiplier' DIP switch beside the blue 'Mode' button. The DIP switch changes the display of the PCI Bus Speed by multiplying the actual PCI bus speed by factors of x1, x2, x3 or x4.

• x1 will show the actual PCI Bus Speed
• x2 will show the AGP Bus Speed (by default)
• x3 and x4 will show the FSB Speed depending on the PCI divider used.
  But it will not be valid if you are using a newer motherboard which uses a 1/5 or 1/6 PCI divider since there's no x5 or x6 option.
  It is also not valid for motherboards that feature PCI bus speed locking.

PCI Bus Data Transfer Mode

The Data Transfer mode shows the amount of data transferred per second, in kilobytes or megabytes. This is useful in determining the efficiency and maximum throughput of the system's PCI bus. However, it cannot show how 'busy' the PCI bus really is. That will be covered by the Bus Utilization Mode.

However, this mode is not very accurate. This is because the PC Geiger assumes that all PCI bus transfers are 32-bit transfers. Even if the PCI bus actually transfers only 8-bits, PC Geiger will still count that as a 32-bit transfer. That skews the accuracy of its readings.

For example, if an 8-bit ISA card sends out 8-bit data on the PCI bus, the maximum data transfer rate should be 4.77MB/s (the maximum transfer rate for any 8-bit ISA device). However, because PC Geiger assumes that every PCI transaction is 32-bits in nature, it will miscalculate the data transfer rate of that transaction as 4.77MB/s x 4 = 19.08MB/s.

Of course, this is a simplistic scenario designed only as an example to show the PC Geiger's potential inaccuracies. In reality, most motherboards will employ byte merging (see the BIOS Optimization Guide for more details) which stores and merges 8-bit and 16-bit data so that they can be sent over the PCI bus as 32-bit transactions. Even if the motherboard does not make use of byte merging, the bandwidth of 8-bit and 16-bit devices is not significant enough to skew the overall results to the point of gross inaccuracy. So this mode can still be considered as accurate enough for practical purposes.