> Back in the ’70s, one relational database did everything. Transactions (OLTP) during the day and reports after hours (OLAP). Databases like Oracle V2 and IBM DB2 ran OLTP and OLAP on the same system; largely because data sets still fit on a few disks and compute was costly.

The timeline is a bit off - Oracle V2 was released in second half of 1979, so although it technically came out at the very end of the 1970s, it isn’t really representative of 1970s databases. Oracle V1 was never released commercially, it was used as an internal name while under development starting circa 1977, inside SDL (which renamed itself RSI in 1979, and then Oracle in 1983). Plus Larry Ellison wanted the first release to be version 2 because some people are hesitant to buy version 1 software. Oracle was named after a database project Ellison worked on for the CIA while employed at Ampex, although I’m not sure anyone can really know exactly how much the abandoned CIA database system had in common with Oracle V1/V2, definitely taking some ideas from the CIA project but I’m not sure if it took any of the actual code.

The original DB2 for MVS (later OS/390 and now z/OS) was released in 1983. The first IBM RDBMS to ship as a generally available commercial product was SQL/DS in 1981 (for VM/CMS), which this century was renamed DB2 for VM/VSE. I believe DB2/400 (now renamed DB2 for IBM i) came out with the AS/400 and OS/400 in 1988, although possibly there was already some SQL support in S/38 in the preceding years. The DB2 most people nowadays would encounter is the Linux/AIX/Windows edition (DB2 LUW) is a descendant of OS/2 EE Database Manager, which I think came out in 1987. Anyway, my point - the various editions of DB2 all saw their initial releases in the 1980s, not the 1970s.

While relational technology was invented as a research concept in the 1970s (including the SQL query language, and several now largely forgotten competitors), in that decade its use was largely limited to research, along with a handful of commercial pilots. General commercial adoption of RDBMS technology didn’t happen until the 1980s.

The most common database technologies in the 1970s were flat file databases (such as ISAM and VSAM databases on IBM mainframes), hierarchical databases (such as IBM IMS), the CODASYL network model (e.g. IDS, IDMS), MUMPS (a key-value store with hierarchical keys), early versions of PICK, inverted list databases (ADABAS, Model 204, Datacom)-I think many (or even all) of these were more popular in the 1970s than any RDBMS. The first release of dBase came out in 1978 (albeit then called Vulcan, it wasn’t named dBase until 1980)-but like Oracle, it falls into the category “technically released in late 1970s but didn’t become popular until the 1980s”