I was learning about the different types of RAM recently (e.g. SRAM and DRAM) and it occurred to me that “computer memory” is just an abstraction. This is obvious once you think about it but I think as a programmer, it’s very easy to not realize this. The idea of memory as a linear array of bits is an abstraction created and implemented by an electrical device.

Most programmers when they think of memory are thinking of virtual memory, which is a completely different abstraction. While it’s also a linear array of bits, the abstraction is created by the operating system and lives at a higher level.

One level below, the abstraction the operating system itself uses — “physical memory” — is the one I’m talking about, created by a a set of electrical devices connected to the CPU with wires (the memory bus).

I’m projecting without any basis, but I presume the reason so few programmers think of memory as an abstraction is because the abstraction is so strong. Nearly all of the time, it “just works” — you write bits and read them out later.¹ The abstraction can leak slightly during programming disciplines that require awareness of low level details like the memory hierarchy and cache coherence (i.e. lockfree) but this is a leak of the abstraction of the memory hierarchy. The core abstraction of physical memory stays in tact — for example, programmers never need to be aware of the internal refresh mechanism of DRAM.²

Of course, you can go infinitely far with this — it’s turtles all the way down.

1. Of course, aside from Rowhammer.
2. My assumption, correct me if I’m wrong.