They also mention casually memory sizes, but 3000T has only 500k of sample memory when doing 4ch+ digital normal mode (4 buffer-2 per ch-1 with digital -0.5 Mpts for ping pong buffers. 1Mpts for Single mode). Scope with 100Mpts will be 100x slower everything else being equal. Scope with 500MPts will have soo much more work to do.
You can keep pulling up the same "small memory" argument, except it is common for memory to change in different acquisition settings across most scopes. Those characteristics are not avoided in the Keysight data sheets or left as only up-to/maximum/peak values, and made very clear in the manuals (contrasting to these other examples discussed here where it is not clear at all what is expected).
But you make the false claim that there is a comparison with memory depth, the waveform capture measurements that competitors use keep the memory depth very short to inflate their numbers. Look at how much slower the competitors are despite choosing less memory! (when at same memory they are far behind). Scopes are not some computer system where the parts are put together in imbalanced ways by the end user, they are a finished product from the manufacturer who has decided on the system performance. Keysight make a real time scope with 100Mpts of memory, the EXR or MXR series, without a significant drop in waveform rate (keeping the system balanced).
Where you keep falling over is trying to make out like all scopes work/function the same. The Keysight megazoom method has been to decouple display and waveform memory, they are two different paths that dont interact. Acquisition data is piped to the display plotter/memory (through decimation etc) separately to the waveform memory. As you say before, to make things fast they chose to put most of the emphasis/features on the decimated view (positive example: fast eye diagrams). Most other scopes draw the waveforms from the acquisition memory, and take measurements from the original data (Lecroy being the extreme example of that, positive example: higher resolution measurements). Completely different with advantages and disadvantages, for comparisons they are best listed as characteristics rather than put as a good/bad binary check box against specific/your preference.
I'm not sure what I wrote was false.
Fact is that real time processing of 250 Mpts is harder than 4 MPts. Which, I agree with you, is no problem if you're sampling at such sample rate and timebase that all scopes take only 1000 samples..
I wasn't attacking anything and was not commenting OP specific results on this test but in general this old (you surely remember massive talk about this on previous many occasions) topic.
Keysight was always big on marketing this Wfms/s advantage (which is real) against other scopes from competition. Always pointing out that this is very important advantage of Megazoom IV to other scopes that don't have it, conveniently forgetting their own higher ends scopes also having 100 Wfms/s if they had same large memory as competition.
And thank you for pointing out that Keysight managed to make new gen of scopes that manage to have large memory and fast Wfms/s. Only problem is that those still barely achieve 200000 Wfms/s, same as lowly 1000X. And that despite massive processing power of high end scope with prices north of 20000 USD.. That shows you what price and performance is needed to make a 200 Mpts scope that will achieve high Wfms/s rates.
So in a range of prices of several thousands USD, compromises will exist. One extreme is 1 MWfms/s on KS 3000T with small memory. Other side is hundredths of MPts at slower update rate.
An it is not about sheer amount of data being processed. It is about architecture that changes with larger memories and high bandwidths needed.
Architecture can be more easily optimised if you have small memory. I suspect KS is using dual port memory architecture somewhere in side Megazoom IV to achieve simultaneous sampling in one buffer and rendering from another to achieve ping pong double buffering.. Or maybe hardware bank switching of memory pages onto two separate address/data spaces.. To achieve bandwidths needed, they use wide words and banks, and interleaving.
Bottom line small memory (full size small memory) allowed them to optimize architecture to fastest possible for fast acquisition in circular buffer/trigger/switch to other buffer/render in parallel.
FPGAs, as powerful as they are, are not as flexible as ASIC, where you can really draw up what you want (*).
That means that even with same sizes of data, Megazoom will be faster. It is optimized for that.
For instance, datapath on Megazoom IV is 8 bit. On SDS2000X+ is 16 bit, courtesy of 12+bit capable architecture.
Etc etc...
I'm not trying to pretend that all scopes function the same way. Quite the opposite. General population are thinking of them like they work the same way. They don't, and those types of comparisons end up being looked upon as comparisons which one is
better, instead of which one is
different and how. And how can you best utilize the tools they provide.
They each are best when used and considered in a specific way. These comparisons end up being perceived as some scoring competition, instead of nice resource for people to dig in to make their own decision based on good quality resource. I believe Rudy's original intention was exactly that.
And I try to explain that and you say the same, except I'm wrong... I think that sometimes you overestimate my English. Although I'm quite eloquent on occasion, it takes a lot of effort to find right words. It is hard to express what you think in foreign language, despite good command of it in general. False modesty on the side, I know my English is quite OK, but far from efortles or perfect.
In a short, I agree with your last paragraph (except first sentence), that is exactly what I try to say. You cannot simplistically compare these platforms based on few numbers taken out of context.
Honestly, I miss MSO5000 from Rigol in this. It would have been good to add it to what so far I see as very good and impartial research by Rudy. There have been quite a few discussions where there are no good info on real performance form real life MSO5000 users. I know there are quite a few of them out there, but maybe one or two contribute quality info.
(*) "I'm not bad. I'm just drawn that way." Jessica Rabbit
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Topic: Functional comparison of R&S RTB2000, Siglent SDS2000X and Keysight DSOX1000 (Read 32181 times)