DB/2 has HOW MANY code bases?

(aka: “Mechanical Sympathy is, very much, a thing”) 

Turns out that DB/2 has FOUR separate code bases for
• AS/400
• MVS
• VM
• R/6000 (originally OS/2)

They’re all, basically distinct lines (°), with Wildly different hardware/OS models. For example, the AS/400 line has a single level store where memory and disk addresses are indistinguishable and objects can transparently move between disk and memory. It’s a capability-based system where pointers, whether to disk or memory, include the security permissions needed to access the object referenced. Why would you not take advantage of this for your features — let alone, for optimization purposes?

So yeah, in this light, it does make sense, especially when you add in the dictum
market share is even more important than engineering efficiency

via — http://perspectives.mvdirona.com/2017/12/1187/

(°) Yeah, VM/CMS is a but of a special case, it’s the productization of the System R research system, and is pretty wildly different, both from a language, and an “under the hood” perspective. Whatever…