>>4473244
Canon naming is moderately retarded. Mk I/II/III/IV are simply more modern versions as you go down the line. There is no similarity in modernity between different models of the same mark.
>1D, 1DX, 1DS etc.
Newstographer/Sports models with higher readouts, bulkier ergos. Nuiances around each specific lettering but they're all about the same.
>5D series
All-purpose Pro model. Full frame, fully functioned. Normally the go-to for consumers on the used market.
>5DS & 5DSR
Same as above but the high-res version. Vaguely in line with the 5D III. The R version rips out the AA filter. Pricey.
>6D
The consumer full-frame. Smaller, cheaper, slightly fewer functions.

>7D
Top-end APS-C DSLR. Think 5D but with a smaller sensor.
>x0D (i.e. 60D, 70D)
Consumer-grade APS-C. Roughly analagous to the 6D series.
>x00 / x50 (i.e. 500D, 450D)
Walmart-tier APS-C. Good enough but definitely feeling the cripplehammer.
>x000 / xx00 (i.e. 3000D, 1100D)
Cripple-tier APS-C. Foregoes the most basic functions in the name of low cost and small size.

>>4446933
>Ultimate in blob technology