PCI vs PCI Express Vs PXIe

[JDParn]

I'm confused about the different Bus Connectors and how to figure out which one works best for my system or even the difference in general. Any help would be much appreciated!

Jaclyn

[Kevin_Price]

A typical modern desktop PC will typically have some PCI Express (aka PCIe) slots.  The number will vary, but somewhere from 2-4 is pretty common.  (There's also a further designation ranging from x1 to x16 that relates to data bandwidth & # of conductors.  An x1 board can be used in any PCIe slot.  Video cards are typically x16 boards and can *only* fit and be used in an x16 slot).

Older desktop PC's tended to have several PCI slots.  PCI is an older technology with more limited bandwidth than the newer PCIe.  Increasingly, one can't assume a new PC will have *any* PCI slots.  They aren't extinct, but if you need to support a PCI board, you need to be careful what desktop you choose.

PXIe is more of an "industrial" bus rather than a "consumer PC" bus.  PXIe boards are not physically compatible with normal desktop PC's.  You would need a special PXI chassis for them.  One would also often buy a special PXI controller, basically a special form factor motherboard that runs a PXI system.

   It has pros and cons, one of the cons being a pretty drastic jump in cost.

People don't generally have a PXI system "by accident" so I'm guessing your system is a fairly standard desktop PC.  If it's less than 5 years old, it ought to support PCIe which will generally be a better choice.  If your system will have multiple DAQ devices that need to be synced, consider adding a "RTSI cable" to share a timing & triggering signal bus among them.  You should also configure MAX to tell it what devices are connected via RTSI.  (This is a "pro" of the PXI platform: such timing connections are automatically present and known by MAX as part of the PXI bus.)

-Kevin P

[crossrulz]

You might also want to give this article a good read: Instrument Bus Performance

[JDParn]

Thank you this clarifies a lot! I do have one more question about connecting to a Laptop instead of a desktop PC.  I know I can get a USB DAQ but the USB seems to have a worse latency and bandwidth. For connecting to a laptop would it be better to just get the USB DAQ or get a PCI/ PCIe DAQ and then a Chasis to connect to my laptop. 

Thank you for all your help!

[JDParn]

Thank you this clarifies a lot! I do have one more question about connecting to a Laptop instead of a desktop PC.  I know I can get a USB DAQ but the USB seems to have a worse latency and bandwidth. For connecting to a laptop would it be better to just get the USB DAQ or get a PCI/ PCIe DAQ and then a Chassis to connect to my laptop. 

Thank you for all your help!

[crossrulz]

What exactly are you trying to do?  Generally, if that latency and bandwidth is an issue, then you will want an embedded controller in a PXI chassis or go with a cRIO.  Again, the options a dependent on what you are trying to accomplish.

[Kevin_Price]

A. RE: USB latency and bandwidth concerns.

   It will depend on your app(s).   In the realm of stuff I've generally done, latency has been a disqualifier much more often than bandwidth.  But many apps can work just fine on a USB device.

B. RE: chassis connected to laptop

   I'm not at all familiar with what you describe.  I'd guess the need to move data between chassis and laptop might still be over USB and still be a possible bottleneck.

-Kevin P

[JDParn]

I'm using the DAQ to control Thorlabs galvo mirrors for a confocal fluorescent scanning microscope. Latency and bandwidth shouldn't be a huge issue, but I do come across species with nano second lifetimes. Therefore, it could be an issue in the long run. I would like to be able to run the system on my laptop, but I'm struggling trying to figure out all the components I need for my computer and how to get them all to connect. 

[JDParn]

What I gather (which could be horribly wrong) is that a chassis can hold one or multiple PCI or PCIe I/O modules and the bus connector for it can be a USB. From this I gather that I can use the chassis as an adapter to connect to my laptop. However, I don't know if this could be better or worse than just buying a USB DAQ.

http://www.ni.com/en-us/shop/select/compactdaq-chassis

[GregSands]

For this application, I'd recommend getting an FPGA card to do the galvo control.  Then it doesn't much matter which bus you use - PXIe, PCIe or USB/cRIO - for control at least.  It may be a different issue if you are also acquiring data quickly on the same bus - then you'd want to make sure you have enough bandwidth to support your data acquisition rate.

Not really related, but I don't think the lifetime of the fluorescent molecule is relevant here - it's more about the time characteristics of your detector (presumably a PMT) and the dwell time of each pixel which is related to the scan rate of your galvo.  Although, the SNR does also depend on getting enough photons in that time window, so you may want to write out a photon budget before constructing, and make sure everything adds up!