The Atom was the first home computer produced by Acorn, the precursor of the BBC Micro. Realeased in 1979, it was a hundred-and-something quid solder-it-yourself box with a 6502 processor, 5 Kb of RAM, a TV output and a jack for a cassette player as storage. The programming language cum operating system was an idiosyncratic variant of BASIC, with a number of features later adopted in BBC BASIC, most notably an inline assembler and various now-commonplace flow-control features designed to encourage structured programming. It was possible to add an additional 8 Kb of RAM, but unfortunately it was not given contiguous memory addresses with the primary memory so you had to write a bit of memory management code to deal with programs which spread across both bits. I seem to recall that you could use the same BASIC line numbers in each section, which could make code a little confusing.
Atom users, with their proper keyboards and assembler instructions, were of course (self-)righteously sniffy about those inferior Sinclair products, where machine code programming involved writing endless POKE statements on a worse keyboard than most modern cellphones. This attitude was continued by association to almost any Z80 based machine, and their successors.