Surveillance technology started with analog which turned incapable in time. Then Hybrid systems; which was tooking analog record into the digital format.
It matured today’s form; digital record, digital store.
And this workflow is being done today via DVR; Digital Video Recorder.
DVR, shooting the digital videos then recording into storage spaces like USB, Computer disc, Optic disc etc.
It is being used since 1999. They generally use H264 and MPEG formats and also record audio. Also can record in SD, HD, 4K and so on.
A lot of brands from a lot of country all over the world producing variable kinds of DVR.
It is also possible to use standard computers with video capture cards to do a similar workflow with similar functions. But big installations with plenty cameras requires an input from a capture card, which is pretty much impossible after a certain number. Increasing inputs requires increased number of capture cards and increased number of computers. So using DVR seems a solid option in the aspect of feasibility.