DOS is an OS.
QuoteDOS is an OS.DOS is a "program loader."Not that that's a bad thing, nor does it disqualify it from being an "operating system."If RPi is toggling a pin at 21MHz, that's without the linux operating system being involved.Talking to IO in fast system is always slower than the internal cycle time. Switching a pin at (relatively) high power at the edge of your circuitry and with a potentially significant load capacitance is "difficult."(You also don't want to look too closely at how slow that RAM memory access is, on cache misses.)
high-speed ADCs with parallel interfaces
What you do with the data is going to make a difference. Hope it's not high-res face or voice recognition.
Quotehigh-speed ADCs with parallel interfacesYou might be able to connect those via the memory interface, or via some sort of DMA scheme. But you probably can't get 100MHz; that's only 10ns for each byte, which is down near the propagation delay for individual logic-gate chips...
Are you making square waves or reading waveforms?
today i get my 68332 cpu
HackaDay seem to be going down hill at a rate of knots!