Monday, August 22, 2011

To run Windows or not to run Windows - All About Oscilloscope Operating Systems

Quick.... look at both of these oscilloscopes.  What's the difference between them?


Both oscilloscopes look awfully similar.  They are both the same height, width, and have the same screen size.  They have the same button layout, and both are available in 350MHz, 500MHz, and 1GHz variants.  What's the difference?
The oscilloscope on the top is a Tektronix DPO4104B, an oscilloscope that uses an embedded Linux operating system, invisible to the user.  The oscilloscope on the bottom is a Tektronix DPO5204, running Microsoft Windows 7 Ultimate 64-bit.

So why do some oscilloscopes run Windows and others run embedded operating systems that are closed?

There is the simple answer.  Lower bandwidth oscilloscopes don't use Windows because the hardware to run it and the license fees to Bill Gates would drive up the cost too much.  Nobody wonders why a $990 TDS2000C doesn't run Windows.

Additionally, the processing power required to run a full load of Windows likely makes the scope bigger and heavier (and take longer to boot), things you do not want in a small bench scope.  The DPO5000 weighs a bit more and is deeper than the DPO4000 (though they look the same from the front).  And as we will discuss, non-Windows oscilloscopes tend to be simpler from a maintenance point of view, a bonus for a scope that might be widely distributed among different users.

On the high end, everybody's oscilloscope runs Windows.  Once you reach 2GHz and above, Windows can be assumed.  Engineers always want to know why can't Tektronix or Agilent or LeCroy make performance oscilloscopes with embedded closed operating systems, or scopes that run MacOS, Android, or anything but Windows?

The simple answer is that as applications get more complex (PCI-Express, Superspeed USB, XAUI, SATA, SFP+, 100G Ethernet, DQPSK, Wideband Radar, etc), the market of users gets smaller.  So much work and development goes into the algorithms for waveform analysis that it makes sense to use the most common environment tools available, such as .NET and MATLAB.  The engineering effort to create a high bandwidth oscilloscope that did not run Windows would not be economically viable at this point today.

Looking at the 4 major vendors of Mid-Range oscilloscopes, you can get into a Windows oscilloscope at the 200MHz performance point (LeCroy WaveSurfer 24MXs-B), 350MHz (Tektronix DPO5034), 600MHz (Agilent DSO9064), or 1GHz (Rohde RTO1004).  You can can stay with an embedded non-Windows OS until you get above 1GHz (Tektronix DPO4104B, Agilent DSO7104B, Rohde RTO1024).

In the graph below, the top 4 lines are non-Windows oscilloscope bandwidth coverage (Blue-Tektronix, Red-Agilent, Green-LeCroy, Purple-Rohde), and the bottom 4 lines are Windows bandwidth coverage.  Tektronix seems to have the most complete coverage in the "overlap" region, with a dual product line from 350MHz to 1GHz, the widest of the field.

So if I want a low bandwidth scope (below 200MHz), it must be non-Windows.  If I want a high-bandwidth scope (>1GHz), it must be Windows.  These decisions are made by the market today based on what is available.   But from 200MHz to 1GHz, how do I decide?

The first decision might be application based.  Some oscilloscope vendors have written test applications geared around a particular platform.  For instance, if you to do full Ethernet compliance test with Tektronix TDSET3, while a 1GHz oscilloscope is sufficient for debug and decode, you need the DPO5104 Windows based oscilloscope for full compliance.  The application is only written for the Windows environment.

Other applications are written for both environments.  For example, there is a need for power supply testing in both platforms, so there are tools like DPO4PWR for the DPO4000 and DPOPWR for the DPO5000.  The same algorithms were rewritten for both platforms.  The Windows variant has some extra analysis features not found on the non-Windows platform, but both are essentially the same.

DPO4000 showing DPO4PWR - NonWindows

DPO5000 showing DPOPWR - Windows 7 64-bit Ultimate
 So if my choice is not made by bandwidth, and my choice is not made by application, what else should I consider?  Often the Windows version of an oscilloscope will have more advanced features than a non-Windows version of the same bandwidth.  For instance, look for extra memory depth for capturing long waveforms, extended trigger capabilities, and additional math and measurement functionality that a vendor may choose to put on a Windows oscilloscope.  Many users want to run programs like MATLAB on the oscilloscope itself and stream data directly into it, so they choose a Windows product.

Many choose Windows based oscilloscopes for their connectivity, from support for thumb drives, Ethernet connectivity, and network printers.  However, even non-Windows oscilloscopes like the DPO4000 now support all of these features.

There are a few cautions when dealing with a Windows oscilloscope.  If you treat it like a scope and never touch the IO ports (USB, Ethernet), you could technically use it as a scope for the rest of your life and never care that it runs Windows.  If it works today, it will work 10 years from now.  I still see some Windows 98 scopes in use out there.

The problem in the real world is that somebody is going to stick a thumb drive into the scope and somebody else will want it on the network.  Instantly you are subject to the needs for corporate security, user accounts, firewalls, virus scanners, spyware blockers, etc.  It is important to be sure that the oscilloscope still runs after your IT department is through with it!

Many vendors publish a document describing the best ways to handle security on a Windows based oscilloscope.  Here is an example of a document published by Tektronix on configuring Windows products.

You should also look at the underlying PC of a Windows oscilloscope.  Some vendors tell you the minimum PC performance in the oscilloscope, and others do not specify it at all.  If the company cannot tell you what kind of PC you will get, this is a red flag to avoid the product.  Similarly, you don't want to spend $10k-$30k and find your product obsolete in 3 years, so I would personally think carefully before buying a product still running Windows XP.  I don't know how long the security support will continue to exist for Windows XP, but for sure Windows 7 will run longer.

For simplicity and ease of use, many oscilloscope users prefer the closed operating systems.  As a result, we are seeing an industry trend towards more advanced "bench" scopes, where application specific software is being written to run on bench instruments.  A Tektronix MSO4104B has power testing, mask testing, basic jitter measurement, screen histograms, 1M point FFT's, tons of measurements, math equation editor, and tons of other features that people think require a Windows oscilloscope.  Yet since it does not run Windows, it is a smaller scope that boots faster and has less security issues.

For the record, I enjoy both tools.  If I had to pick only 1, I would have to go with the Windows based oscilloscopes merely because that's where all of the heavy duty analysis tools exist.  But for general debug, I still prefer my Tektronix MSO4104B, a great scope that does not run Windows.


  1. Great job, I really like your chart of windows to non-windows comparison between the vendors.