The early computers of the vacuum-tube age were marvels of engineering for their time. Today, we can simultaneously appreciate the advances these computers represented, making previously unthinkable computational work possible, and chuckle at what to us seems like their ludicrous size and painfully slow processing speeds.
But while you probably know ENIAC took up a whole room, you probably don't know that it just up and stopped working -- a lot. The vacuum tubes that made up its guts would burn hot and eventually fail -- and there were so many of them that this would happen every couple of hours. The reliability that solid-state electronics provided was at least as important an advance as improved speed and size.