As usual, determining a calculator's importance in history is a largely subjective matter. Every machine will have its fans, claiming for their beloved machine all the possible titles or records.
The first personal computer?
There are people today that claim that the Programma 101 was
the first personal computer. Amongst them, Ing. Perotto, the
inventor of the machine, that in his recent book Programma
101, l'invenzione del personal computer raises this claim
too.
In my opinion, the Programma 101 is a programmable calculator, not a computer. The difference might be sometimes subtle, but the high-level machine operations are quite typical of a calculator, not of a computer. The miminum data entity that the P101 can handle is a signed, 11-digit decimal number with decimal point, not a binary word.
This is not to be taken as a deficiency: as Perotto clearly states, the high-level instruction set was designed on purpose to make the machine easier to use. At the time the P101 was introduced no other machine had such a user-friendliness.
Anyway, it must be said that at that time the idea of "programmable calcuator" was at that time quite indifferentiated from "computer". The U.S. press coverage constantly speaks of the Programma 101 as of a computer, and unanimously stress the "desktop" nature of the P101.
Already in 1971, G.C. Bell wrote: The Programma 101 is at the limit of what we call a stored program computer.
The first programmable calculator?
Again, this is not correct. There are lots of examples of older
programmable calculators (e.g. Zuse's machines, completely built
with relays and dating back to the '30s).
But then what?
The Programma 101 is anyway an historically important machine:
it definitely was the first computing machine that for its price
range ($3.200 in 1965) could be bought even by small-medium companies.
Not really personal ($3.200 was comparable to a year's wage),
but definitely going in that direction. Compare its price with
the $25.000 of the PDP-8, already a budget machine for the time,
and you will see what I mean.
At least, its historical role is well shown by the huge number of P101s that were sold - 35.000 to 40.000. I would say this must be about as much as the sum of all the other programmable machines that had come before. It was "the first machine" for a huge lot of people, and most of the mentions you find of it is of people that say things like "I began programming in 1969, on an Olivetti Programma 101...".
Technologically, there are a few features that make it incredibly modern for the times and that are found on most programmable calculators still today, like the jump instructions that can be invoked with the press of a single key (like function keys), or the Start/Stop instruction (S) that toggles the execution status of the machine.
The magnetic cards were also a very innovative, and the patents applied on them earned to Olivetti a good deal of royalties. HP alone had to pay a total of about $900.000 for the use of the magnetic cards (and other technology) in the HP9100 series.
But why is this machine so little known?
There have been a lot of "missed occasions" in the
P101's commercial exploitation. Olivetti had in that period very
little trust in the future of electronic calculators. The company
was almost a world leader in electromechanical machines like
the Divisumma series and was in those years crossing a deep managerial
chrisis. The electronics division had been sold to General Electric
at the beginning of 1965, and very few people were kept in Olivetti
with knowledge in electronics.
When Perotto had the machine ready for the 1965 New York exposition, the conservative management had an enormous booth built to show off the new Logos 27 electromechanical calculators, and the P101 was hidden in a tiny room
An image from an ad.
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