That would make an 8051 a microprocessor. as a rough guide to usage, Google has it's advantages:
19,200 hits for "8051 microprocessor".116,000 hits for "8051 microcontroller"
So "8051 microcontroller" is six times more common than "8051 microcontroller"
First of all, the original question that you allude to is "how many angels can stand on the point of a pin", not "how many angels can dance on the head of a pin" and the dispute was between "an infinite number" and "an arbitrarily large but finite number."
Thomas Aquinas (1225-74) the main architect of Roman Catholic theology, spent much of his life exploring this question. He reasoned that it is impossible for two distinct causes to each be the immediate cause of one and the same thing. Following the standard methods and intellectual climate of his time, he framed such scientific and mathematical questions in religious terms and chose an angel as a good example of such a cause. His argument was that if two angels occupy the same space the question of which one is the cause of an event is indeterminate. This can be seen as an early attempt to deduce the Pauli exclusion principle.
Aquinas could not not place an upper bound on the density of angels in a small area, because the size of an angel was undefined and could be arbitrarily small.
In 1995 by Dr. Phil Schewe, spokesman for the American Institute of Physics, revisited this problem. He chose his smallest possible angelic size from the superstring theory that space is not infinitely divisible and thus the smallest possible angel is at least 10 to the -35 meters in size.
He chose his smallest possible pin point as being the tip of the an IBM scanning tunneling microscope which has a tip that tapers down to a single atom. This reduced the calculation to a simple multiplication problem which I will leave as an exercise for the student.
Schewe, however, assumed without questioning that Thomas Aquinas' non-overlap theory was correct. Anders Sandberg of the Royal Institute of Technology, Stockholm, Sweden questioned this assumption. He argued that, since angels can be presumed to obey quantum rules when packed at quantum gravity densities, the uncertainty principle will cause their wave functions to overlap significantly even if there is a strong degeneracy pressure. Without the non-overlap assumption Schewe's approach cannot derive an upper bound.
Sandberg then turned to information theory for a solution. First, he assumed massless angels (if the angels have mass, the point of the pin will collapse into a black hole) containing at least one bit of information: fallen/not fallen. Assuming a pin point that is one iron atom, he use the Bekenstein bound on information to calculate an upper bound on pinpoint angel density of 2.448 times to the -5 angels, far below the Schewe bound. He also calculated friction effects, but these can be ignored because he incorrectly had the angels dancing instead of standing. My own contribution to this was to observe that it takes at least two locations per angel for them to dance. If they are packed at maximum density, they can't move. Also there are angular momentum issues if they dance the twist.
Given the extensive research already done on the question of how many angels can stand on the point of a pin, I was heartened to see you ask how many micros can dance on the head of a pin. It happens that I am well-qualified for examining this, having done extensive work with the smallest known microcontrollers; bare dies with wire bonding that is covered with blobs of epoxy.
On would think that the lower limit would be set by complexity and feature size, but at the low end the wire bond pads take up most of the room. Assuming a one millimeter pin head and a dance caused by Brownian motion, and assuming a micro that is optimized for minimum size, I estimate that seven micros in a hexagonal array can dance in the head of a pin. Future advances in wire-bonding technology may improve this figure.
I hope this helps.