What was it like?

I learned my software skills on the Ferranti Mercury computer. It had as I recall 468 words of memory (a word is about 6 bytes so call it 3k bytes).   Let's see, my phone has 8,000,000,000 bytes - that's about 2.5 million times more.  My phone makes the 1500 instructions per second look pretty silly as well.

The computer was big. The electronics used valves and they get hot. So each cabinet has a refrigerating unit built-in, and they were noisy.