My first computer was a Sinclair ZX81 with 1k of memory. I didn't bother upgrading it because the spectrum was due out soon and I only wanted the ZX81 to see if I was interested enough to buy the 48k (woo big memory) Spectrum
My first actual PC was an Olivetti M24. An interesting machine. It actually had 2 motherboards. One accessible from inside the PC in the normal way and one by removing the bottom of the machine.