If you had a 16 kB memory card (a.k.a "Language Card") you could overlay the ROM memory with RAM, and load the Integer Basic ROM overe the AppleSoft Basic ROM.
AppleSoft did "everything" with floating-point variables, like loops indexing into arrays. It's amazing that programs ran at usable speeds on a 1 Mhz machine.
My C64 didn't come with a monitor. I typed one in from a magazine, then learned assembly by entering instructions directly into it. I was so thrilled to discover assemblers later.
I thought I was in heaven when I got the Action Replay cartridge (not the genuine, but a clone with the same software) that came with a monitor, a "freezer", fastloader, and various disk utilities.
> The era in which there was nothing but assembly language was very short-lived.
Hell, I'm not even sure the era existed.
Grace Hopper was creating the first few high level languages for UNIVAC I. A-0 was complete in May 1952. A-2 (the first which saw extensive use) was created in August 1953.
As far as I can tell, UNIVAC I never had an assembler. If you weren't using A-0, programmers were expected to just type in raw machine code. Here is a UNIVAC programming manual from 1953 [1], and there is no mention of an assembler. Oh, and if you think you see instruction mnemonics... no, those are just letters which the CPU instruction maps onto.
Over in the IBM world, at least the 701 launched with a proper symbolic assembler in April 1953. But it also launched with Speedcoding [2], a somewhat higher level language halfway between non-symbolic assembler (it decodes mnemonics, but the programmer has to specify all addresses as absolute numbers) and an interpreter.
None of the other early computers seem to have had assemblers (though some, like the Manchester Mark 1, had high level languages).
There might have been some programmers at IBM who might have had access to a the prototype 701, and the symbolic assembler before Speedcoding existed [3]. But for everyone else, they seem to have gotten access to high-level languages at the same time, or before they got access to assemblers.
[3] It's also possible that Speedcoding development was largely finished before the first 701 was operational. I'm finding it hard to find exact dates for that.
Part of the problem is that "Assembly language era" is ill-defined. Personally, I don't think it counts as Assembly language unless you are using a symbolic assembler, because that's what modern programmers think about when you say "assembly".
There is a reasonably common interpretation includes the whole machine code era as "Assembly language", as you are writing it out and then hand-assembling it. Which means the UNIVAC's C-10 machine code counts as "Assembly language", even if they weren't using that terminology. With this interpretation, the "assembly language era" lasted a few years. but I think this inspiration is very misleading to any programmer exposed to a proper assembler.
Anyway, even with my stricter definition, there was an assembly-only era, but it only seems to have existed inside IBM's research labs. They had their first symbolic assemblers running on the "test assembly" by October 1950.
There is very little information about this "test assembly" computer on the internet, doesn't even have a wikipedia page (same with the "Tape Processing Machine" or TPM that followed). But "IBM's early computers" by Charles J Bashe documents it. This computer had not one but two symbolic assemblers running by autumn 1950, which does actually seem to beat most high level languages.
Long before the first 701 was even installed (in April 1953, at IBM's HQ), programmers had already gotten sick of assembly programming, which is why speedcoding was created.
Though, this wasn't just internal IBM programmers. Customers who bought the 701 were given documentation about both the computer and the assembler as early as 1951. These customers had hired programmers, who had started writing assembly code, months before the 701 assembler was even debugged and running on the first prototype 701, and years before they received their computers. So maybe there was also an "Assembly language only era" in the offices of these early 701 customers. But it's kind of an edge case if they didn't have a computer to run the assembler on, or test their programs.
I assume these early programmers were occasionally visiting the prototype 701 to assemble and test their code.
By the time the 1950s were over, we had higher level languages.
Like before The Beatles recorded their first album.