Many of today's embedded systems require looking at more than just the 4 analog channels on a scope. Digital scopes have integrated logic analyzer style inputs and created MSOs that can show up to as many as 40 channels. MSOs exist in two distinctly different form factors.
1) Some scope vendors been elected to offer 16 or more digital channels fully by adding hardware inside the MSO. This creates new models MSO scopes that require buying a new scope. MSO Dedicated Scope Example 1
2) Other vendors create the MSO option by adding hardware outside the scope with up to 36 digital channels inputs. This lets the option be used with any like scope and untether if the scope is needed somewhere else without disconnecting and reconnecting 36 channels of micro-grabbers. MSO Option Example 1
Would MSO functionality make screen size and CPU speed very important specifications?
Yes, the higher the MSO channel count, the more important screen size. Industry highest maximum analog BW on the MSO digital lines is 500 MHz with 2 GS sampling. Deepest memory is 50 M samples per digital line. This represents a large amount of data. Evaluations are suggested as processing speeds vary greatly.
MSO features usually provide automatically time correlated analog and digital presentations on the scope's display. While some provide cross triggering where both analog and digital conditions are considered prior to triggering, the conditionality is relatively simple compared with logic analyzers.
Can MSO inputs be used for serial data like I2C?
Yes. Freeing analog channels for analog signals and give the scope the ability to trigger on a specific I2C address, sub-address, etc.