Until the nineties of the last century, quantum computing seemed to be an interesting theoretical possibility, but it was far from clear whether it could be useful to tackle computationally hard problems with high relevance for actual complications. This changed dramatically in 1994, when the mathematician P. Shor announced a quantum algorithm that could efficiently … Continue reading Shor’s quantum factoring algorithm

# Month: November 2018

# How does multitasking really work?

The first PC on which I was running a copy of Linux back in the nineties did of course only have one CPU, so it was clear to me that it could physically only execute one instruction at a time - but still, it magically created the impression to run several programs in parallel without … Continue reading How does multitasking really work?

# The quantum Fourier Transform

We are getting closer to the most spectacular early quantum algorithm - Shor's algorithm for factoring large composite numbers which can be used to break the most widely used public key cryptography systems. But before we can tackle this algorithm, there is one more thing that we need to understand - the quantum Fourier transform. … Continue reading The quantum Fourier Transform

# Interrupts – the heartbeat of a Unix kernel

Modern operating systems are mostly event driven - network cards receive packets, users hit keys or a mouse buttons, built-in timer create events or data arrives from a hard drive. To be able to process these events, a CPU needs a mechanism to stop whatever it is currently doing and run some code designed to … Continue reading Interrupts – the heartbeat of a Unix kernel