Comparing memory depth on two different scopes

[Frank_38]

Hi,
while trying to learn more on how scopes work and what their various specs means, I have been comparing a few ones. More specifically I was looking at a Rigol MSO5104 and a Keysight DSOX4154A. I know that these two scopes are vastly different in specs, and maybe it's even meaningless to try to compare them, but one thing that surprises me is the memory depth. The MSO5104 has 100Mpts and the DSOX4154A has only 4Mpts. It seems really low, specifically for such a high-end scope. Am I missing something obvious here?
Thanks in advance for your help.

[Domitronic]

No, the Keysight really falls behind the competitors in terms of memory. Thats related to the old ASIC they are using.

As always, all scopes have advantages and disadvantages. And memory is certainly not a strenght of the Keysight scopes up to the DSOX4000 range. The InfiniiVision range is also not what Keysight considers as high end. In the Infiniium scopes like EXR or MXR they have around 800MPts or 1,6GPts as far as i know.

[Frank_38]

Ok, thanks for your answer

[Fungus]

Am I missing something obvious here?

The relative age of the designs.

Also: Keysight put their RAM right inside their ASIC but Rigol uses external RAM ships. The Keysight RAM is a lot faster access for heavy processing. The Keysight is famously fast and doesn't slow down even if you turn everything on. Moral: Not everything is visible by looking at numbers on spec sheets.

OTOH... 4Mpt is a bit small these days, yes. Whether it affects you will depend on how you use it. 4Mpts is plenty for just looking at signals on screen and analyzing them but for things like serial decoding it's good to have a lot of RAM so you can do a long capture then zoom in.

[wraper]

The problem with most of less expensive (and many expensive) large memory depth scopes is that they really suck when large memory depth is used. UI becomes really sluggish, waveform capture rate drops dramatically, and so on. Specs like capture rate are usually given only in best case scenario, when combined with memory depth or math functions, often there appears a problem. Keysight scopes on other hand almost always work with max memory depth with all of that high capture rate and responsiveness. Need to be aware of that and do your own research when making a choice.

[Domitronic]

Yes, i agree. At work we have Tek Series 4 and Keysight DSOX3000. Tek has more than 15 times the memory. But its slow and becomes very slow and sluggish as soon as you turn measurments on. A nightmare in terms of usability. Keysight remains fast no matter what you do but lacks the memory. So as said above, every scope has advantages and disadvantages.

[nctnico]

Yes, i agree. At work we have Tek Series 4 and Keysight DSOX3000. Tek has more than 15 times the memory. But its slow and becomes very slow and sluggish as soon as you turn measurments on. A nightmare in terms of usability. Keysight remains fast no matter what you do but lacks the memory. So as said above, every scope has advantages and disadvantages.

Another thing to consider here is that Tek uses the actual waveform data versus Keysight using decimated data for measurements.