The first computer I was allowed to hack was an IBM 403 printer, which I used for a Boy Scout mailing list. We weren't allowed to mess with the wires on the plugboard, so it may not count, but we could do anything we wanted with the paper tape, punch cards, and card sorter. It had very little internal memory, but it could fit a big stack of cards; 1000 cards * 80 columns = 80K bytes, and I think the character set had 48 values (so you could call them 5.5-bit bytes if you wanted.) And the Model 026 keypunch ran on vacuum tubes.
The PDP-11 probably had 24KB of RAM, maybe 32KB. I think they upgraded from an 11/20 to an 11/44 after a year. It was based at the local university, and a dozen or so high schools time-shared on it, using RSTS-11 and programming in BASIC, with Model 33 ASR teletypes.
The first computer I owned was an HP programmable calculator (I forget if it's HP-21 or HP-25. 49 words of program memory, 4 words of stack.) The next computer I owned was a retired 386, because there was no point in owning a home PC when I had a terminal into the machines at work.
The first computer I ran myself was a VAX 11/780, which had a huge 4MB RAM that required two cabinets. Our application really needed 12MB, so I played a lot with virtual memory for a few years; after a few years chip densities improved and we were able to afford to upgrade it to 16MB, and suddenly the application ran in an hour instead of a week. (We could have probably done that upgrade a year sooner, saving a lot of work and getting better results, if the bean-counters hadn't thought that capital budgets and labor costs were entirely different kinds of money.)
My current work computer has 4GB of RAM, and [grumble] 32-bit Windows on it, which is the current annoying-640K-equivalent. The hardware would be fine with a 64-bit OS, but the IT department isn't. I am connected into a larger VMware server, which probably has 48GB, and most of my VMs are 1-2GB. And I've also got a window connected to Google - I don't really know how much memory it has