Honeywell's systems division is the DCS. TDC 2000/3000 were early and mid era versions. Plant-this and Plant-that seemed to be later versions. Experion is the current DCS brand name. Controllers are H200 & H300. Except for brochures with glossy photos, details are pretty well obscured for those not registered as users. If there'a a public forum for Honeywell DCS, I've never found it.
Honeywell's instrument group (recorders/controllers/analytical instruments/field transmitters) markets the HC900, best categorized as a Process Automation controller (PAC). It is controller based, multiple rack mounted I/O modules, native Modbus RTU/TCP with provision for redundancy for ethernet communications, control and power supply, but no redundant I/O. It's analog throughput is 500mS for up to ~1,000 points. Discrete scans are somewhere around 25mS. It's programming language is tag based function block, is OPC friendly, but it does not do ladder logic. So, the HC is not a general PLC for machine control, it fits well in the controller-based process loop control market.
The DCS's have integrated server-based database, graphics for HMI, historian, etc. that are typical of DCS, whereas the HC is controller based, like a PLC.
Honeywell bought a PLC company back in the 1980's (?) and that 6xx series PLC was used for discrete logic control along with the separate S9000 analog controller of the same vintage.