There were several generations of sequencers, and the driving idea is to cut the DNA in very very short pieces that could be analyzed separately and accurately.
However the tiny reads have to be reassembled and it is a hard challenge. So much for all the pop science articles.
There are sequencers that are able to process long reads. Not surprisingly their error rate is awful.
Oxford Nanopore smallest sequencer (as big as a USB dongle) is still valuable with lot of data processing.
Their core idea is to make a DNA molecule go through a nanometer pore, and to measure how the current flow is varying as each nucleotide goes through the pore.
Basically their device is very similar to a water reverse osmosis unit with an electrical potential applied to the water chamber.
Indeed the number of pores must be as low as possible, however if DNA is tiny in width they are one meter long! So in a tiny space there are not a lot of DNA.
Enjoy this project?