First post from new member...
I have been in computing (among other things) since the mid 1950s when a friend and I built a "computer" in the basement. In quotes because it used all vacuum tubes and electro-mechanical relays and as high school students, we could not afford any memory. Could add and subtract -- sort of.
First real machine I ever used was an IBM 704 main-frame with 5000 or so vacuum tubes and lots of diodes. It had 32768 words of magnetic core memory. It did do floating point arithmetic (36-bit machine, but used 2 words for a floating point number). I later used solid state machines, like IBM 7090. My first minicomputer was one I got the company I worked for to buy. We had 16384 24-bit words of memory and two hard drives, each the size of a washing machine. Honeywell DDP-224. I wrote the OS for it.
I also wrote a lot of program for the IBM System/360. I then did a lot of work with UNIX from early 1970s to about 1989 when I retired from there. I then worked about 4 years in another place where I wrote telephone communication code in C++. I am retired now, but still do some coding for my main computer which I built from parts (i.e., boards, processors, hard drives; I did not buy transistors, chips, diodes, ...). It has 2 Xeon processors, 8 GBytes RAM, and 6 Ultra/320 SCSI hard drives and 13 fans (not enough fans, but I cannot put any more in).
It is an overpowered desktop that also serves my old machine which is a little like this one, but only 3 hard drives and 512 Megabyte ram.
I guess that is enough to start with.