M4i.22xx Transfer speed and speed test results

Streaming Transfer Speed

The M4i series is able to reach around 3.4 GByte/s of streaming transfer speed on high-performance motherboards with 256 byte payload size and around 3.0 GByte/s of streaming transfer speed on standard motherboards with 128 bytes payload size. This figure is given in the data sheet and defines the speed the PCIe interface of the Spectrum cards is able to reach.

A list of tested motherboards can be found here.

Limitations of M4i.22xx series

While the M4i.22xx series has the same fast PCIe interface like the complete M4i series the memory controller is getting into limitation in some cases: the memory controller used on the M4i.22xx card is able to do a throughput of around 7.5 GByte/s in sum. When using the M4i.22xx card with full sampling speed of 5 GS/s (5 GByte/s of data storage into memory) there is around 2.5 GByte/s of throughput left for data transfer over the PCIe bus. This throughput limit will have some small consequences on the usage of the card.

Please note that a sampling of 5 GS/s is equivalent to 1 x 5 GS/s or 2 x 2.5 GS/s or 4 x 1.25 GS/s

• Single shot acquisition with data readout after acquisition has finished: no limitation
• Continuous streaming mode with 5 GS/s: the throughput will be limited to 2.5 GByte/s instead of the theoretical 3.0 to 3.4 GByte/s. As consequence the maximum acquisition time until the buffer has an overrun is a little shorter (25% to 30%) than expected.
• Continuous streaming mode with 2.5 GS/s or less: no limitation as transfer bus speed can go up to PCIe full speed.
• Multiple Recording or Gated Sampling with 5 GS/s: during acquisition time the transfer speed will drop to 2.5 GB/s while it is 3.4 GB/s during the gaps. In total the consequence will depend on the ratio between acquisition time and gaps. In most cases the internal additional FIFO buffers will equalize this and you won't see any difference between theoretical throughput and limited throughput. However there might be some limitations whenever one is getting near the theoretical maximum of throughput.

Speedtest of Control Center

As the Spectrum control center is switching the card to a special internal test mode where the maximum speed is used you will always see the limited transfer speed of roughly 2.5 GByte/s.