If computers were fully deterministic, we wouldn't need error correcting ram.
The abstracted design of the machine is meant to be deterministic, but you can't predict before running any command whether or not it will complete because there are externalities that effect the outcome.
Electromagnetic interference even happens in-chip where an electron can accidentally escape it's wire and enter another, possibly resulting in an error, but not every time.
It's even been used as an attack vector where rapidly flipping a bit increases the likelihood that a neighbor bit is also flipped, but the method is probabalistic, not deterministic.
As long as the machine is part of the larger universe, and not completely isolated in its own bubble of space-time (an impossible situation, an object without an environment) - it cannot be purely deterministic because of the fundamental nature of physics.
Arithmetic is deterministic, because it is abstract. A calculator or computer is not, because it is physical and exists in a non-deterministic universe. But with error correction, etc., it's deterministic enough for practical purposes. For more in-depth explanation, start with https://en.wikipedia.org/wiki/Indeterminism
The abstracted design of the machine is meant to be deterministic, but you can't predict before running any command whether or not it will complete because there are externalities that effect the outcome.
Electromagnetic interference even happens in-chip where an electron can accidentally escape it's wire and enter another, possibly resulting in an error, but not every time.
It's even been used as an attack vector where rapidly flipping a bit increases the likelihood that a neighbor bit is also flipped, but the method is probabalistic, not deterministic.