There are two main advantages of PCI Express-based instruments compared to the 66 MHz and 33 MHz PCI buses:

- PCI Express x1 is a modern industry standard that has been adopted by most PC motherboard manufacturers.

- Significant increase in continuous streaming speed when using multiple instrument cards.With the older 66 MHz or 33 MHz 32-bit PCI buses, the maximum transfer rate is shared by each installed device, whereas with the PCI Express x1 bus every device has a maximum continuous data transfer rate of 150 MBytes/s.

As an example, we can compare the performance of three PC’s using different PCI bus systems and each having four instrument cards installed:

	Maximum sampling rates
PCI	1 card	2 cards	4 cards	Total
33 MHz / 32 bit	100	50	25	100
66 MHz / 32 bit	225	112.5	56.25	225
Express x1	150	150	150	600

As can be seen by the table above, with PCI Express the total system data transfer bandwidth increases with each device installed while with older PCI the bandwith remains the same but is shared. With four cards, the total continuous transfer rate of the system is approximately 600 MegaBytes per second, more than 2.6 times higher than 66 MHz PCI or 6 times faster than 33 MHz PCI.

The benefits of PCI Express

• Reduced time to off-load measured data leading to faster test times
• Reduced system cost. More user applications can stream recorded data direct to PC RAM or hard disk, saving the cost of expensive onboard instrument memory.
• Longer recording times. The user can record fast signals for a much longer time either to PC RAM of hard disks. Note: Windows/Linux 64-bit drivers can be used with PC’s having up to 128 GByte RAM.
• Increased real-time performance. Faster data transfer widens the possibility for real-time processing and quicker online displays.

Summary

If your application requires the fastest streaming performance but you only require one instrument board, then the UF2 series of cards using the 66 MHz PCI bus is most likely the best choice. However, bear in mind that any other device on the 66 MHz PCI bus will also use the bandwidth and that this is not always as obvious as other installed cards. Check the motherboard block diagram to make sure motherboard located peripheral chips such as Gigabit Ethernet are not connected to the 66 MHz PCI bus!

Note that while it is possible to use the UF2 cards in a 33 MHz PCI slot the streaming performance will be as a 33 MHz PCI card in the above table.

However, if your application requires multiple boards then the UF2e cards and PCI Express will give the best system performance.

Further system performance improvements are possible if multiple cards are distributed across multiple PC’s and synchronized using the System Star Hub option.