In the book, the device stores "half a million words". Sheesh, my mid-priced data stick is a gigabyte. We're out racing the masters.
Now, I admit that when I read classic Sci-Fi I can tell a lot of it was written before microchips were even invented. I found it funny when reading The Moon is a Harsh Mistress that Mannie (the one armed computer technician) is so concerned about dust getting into the super computer, Mike. Back when Heinlein was writing this book, most "computers" took up entire floors of buildings and were very susceptible to things like dust and dirt. It makes sense that he would write his stories that used the same concepts.
Heck, peel open any of the computers at my house and you'd find about 20 pounds of the stuff.
Another "faster than Sci-Fi" event is the communicator from Star Trek. Today, we call them cellphones.