Hi you have two options really,
There are two modes of operation, streaming mode and block mode. Streaming mode does not utilise the memory of the device and streams straight to the PC memory. Block mode samples data to the devices internal memory then transfers it to the PC.
There are two oscilloscopes that I would recommend.
You can get up to 1MS/s for the 3424 for continuous streaming if you were to write your own software. If you are using our software you will get about 2 seconds worth of data for all 4 channels in streaming mode with the settings you defined (there is a limit set in our software as to how long you can stream for, however if you were to write your own software it can be as long as you wish). In terms of block mode, the device has an internal memory of 500kS and as such the greatest length of time you will get with the settings you have chosen is also 2 seconds.
The other option is the 4424 in streaming mode using our software you will get about 20 seconds worth of data (again there is a limit set on our software), however if you were to write your own software, depending on your PC spec there is no limit to how fast you can stream (with a good PC you can get 10MS/s and upwards). In terms of block mode you will get about 5 seconds worth of data.
Hope this helps.