DRAM memories made with special CRTs with memory have been used for a few years, until 1954. For instance the first generation of commercial electronic computers made by IBM (scientific IBM 701 and business-oriented IBM 702) have used such CRTs.
Then the CRT memories have become obsolete almost instantaneously, due to the development of magnetic core memories, which did not require periodic refreshing and which were significantly faster. The fact that they were also non-volatile was convenient at that early time, though not essential.
Today, due to security concerns, you would actually not want for your main memory to be non-volatile, unless you also always encrypt it completely, which creates problems of secret key management.
So CRT memories have become obsolete several years before the replacement of vacuum tubes in computers with transistors, which happened around 1959/1960.
Besides CRT memories and delay line memories, another kind of early computer memory that has quickly become obsolete was the memory with magnetic drums.
In the cheapest early computers (like IBM 650), the main memory was not a RAM (i.e. neither a CRT nor with magnetic cores), but a magnetic drum memory (i.e. with sequential periodic access to data).
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DRAM memories made with special CRTs with memory have been used for a few years, until 1954. For instance the first generation of commercial electronic computers made by IBM (scientific IBM 701 and business-oriented IBM 702) have used such CRTs.
Then the CRT memories have become obsolete almost instantaneously, due to the development of magnetic core memories, which did not require periodic refreshing and which were significantly faster. The fact that they were also non-volatile was convenient at that early time, though not essential.
Today, due to security concerns, you would actually not want for your main memory to be non-volatile, unless you also always encrypt it completely, which creates problems of secret key management.
So CRT memories have become obsolete several years before the replacement of vacuum tubes in computers with transistors, which happened around 1959/1960.
Besides CRT memories and delay line memories, another kind of early computer memory that has quickly become obsolete was the memory with magnetic drums.
In the cheapest early computers (like IBM 650), the main memory was not a RAM (i.e. neither a CRT nor with magnetic cores), but a magnetic drum memory (i.e. with sequential periodic access to data).