In my case it began with 16K (yes, 161024 bytes) and 90K (yes, 901024 bytes) 5.25" floppy disks (although the floppies were a few months after the computer). Eventually upgraded to 48K RAM and 180K double density floppy disks. The computer: Atari 800.
I'll see your Atari 800 and raise you my Atari 2600 with its whopping 128 bytes of RAM. Bytes with a B. I can kinda sorta call it a computer because you could buy a BASIC cartridge for it (I didn't and stand by that decision - it was pretty bad).
I thought the timex Sinclair 1000 win 2 Kbytes of ram was bad.
The membrane keyboard wasn’t great (the lack of a space bar was a wierd choice) but it did work. We had programs on casette and did get the 16Kbyte memory expansion.
https://en.wikipedia.org/wiki/Timex_Sinclair_1000
I didn’t realize the Atari 2600 had basic, always thought of it as a game console.
You can buy this bad boy [attiny11] with no ram, only registers.
https://ww1.microchip.com/downloads/en/DeviceDoc/1006S.pdf