Moder scopes use pipeline ADC, which is essentially cascaded flash ADC+DAC pairs.
There are various pipelined configurations. Some take one bit at a time, and look a lot like an SAR converter where the stages are spatial rather than temporal. Its quite common to be like the first pipelined converter I used in the late 1970s, where each stage deals with 2 bits. These are often drawn in data sheets like they are a 2 bit ADC, a 2 bit DAC and an analogue subtracter at each stage. However, the ones I've seen the detailed internals of actually use a single analogue block that outputs 2 digital bits and passes on the analogue residual without any clearly distinguishable DAC.
Don't trust the block diagrams in modern data sheets too much. They conceptualise a lot of what is going on to illuminate functionality, rather than implementation details. For example, most ADCs showing a PGA at the input don't actually have an amp there at all. Its all done my smoke and mirrors... or sometimes by switching capacitors or current feed resistors.
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