Ah, but most of those 64MB (remember, 1024kB in a megabyte, so 65565kB/1024kB = just over 64MB) are what's known as expanded memory. The original IBM PC was limited to 640k of RAM because the 8088 CPU could only work with 1MB total, and some room had to be left over for address space. DOS was originally written with this in mind, and in order to maintain backwards compatibility, later versions of DOS kept this limitation, even when CPUs like the 286 and 386 came along which supported more memory. Anyway, programs written for these CPUs (more commonly the 386 since the 286's protected mode was flawed) could use the extra memory through what is known as "protected mode", but in order for a protected mode program to start, you have to execute it from the 8088-compatible DOS "real mode" environment, and as such you still have to have at least some free conventional memory, or "real mode" memory.
That's kind of a flawed, simplified explanation of it. The point is that no matter how much ram you have installed beyond 640k, in DOS you're still going to have to have some free memory below 640k in order for things to run. There is no "magical" way to have more than 640k of conventional memory, though there are all sorts of tricks that allow you to minimize usage of it, such as by loading certain device drivers "HIGH" in CONFIG.SYS.
It's been a long time since I've actually CONFIG.SYS on an actual DOS machine (thanks DosBox! 😁), but if you're running DOS 6.22 and you want to squeeze out a few extra crucial KB of conventional memory, try running MEMMAKER.
