No fan, because the fan is the first thing to die.

They are industrial units meant to live where a normal computer does not live. No fan: the heat is taken out through the casing itself, which acts as a radiator. No spinning drive, solid-state memory instead. With a declared working temperature range that goes well beyond that of an office machine, and often powered at twelve or twenty-four volts rather than off the mains, so they can hang off the same supply as the rest of the electronics in a cabinet.

They usually bring things a server does not have: rail mounting inside an electrical panel, inputs and outputs to talk to other equipment, serial ports for old electronics, and sometimes a connection for a mobile modem. Those are the details that turn a computer into a device you can fit on a wall.

At a remote point with few cameras: an outlying industrial unit, a car park, a pumping station, a substation. There you need to record on site because the line back to the centre will not take all the video, and there is no room, no air-conditioned cabinet and nobody who is going to maintain a server.

At the edge, doing the work before sending: analysing what happens on a few cameras right there and sending only what matters to the centre, instead of pushing all the video up. That changes the sum on the communications line, which at remote sites is what costs the most.

And as the controller of one particular point: the electronics of a barrier, the unit that reads number plates at an entrance, the one that gathers the signals from a panel. In all those cases what counts is not the power: it is that it works for five years in a place that gets hot, is dusty and nobody goes into.

You gain being able to install where there was no space, and you gain mechanical reliability: with no fans and no spinning drives there is far less to break. You gain low consumption, which matters a great deal at a point fed by a small backup, and you gain the installation itself: in a street cabinet or on a panel rail it fits where a server does not go.

You lose capacity, and it is worth saying how much. Less power to decompress and analyse video, so the number of cameras it will take is modest and has to be measured instead of assumed. Fewer bays, which means few days of recording unless you hang storage off it. A single power supply, with no redundancy. And less room and less heat dissipation for a graphics card: there are units of this class that accept acceleration, and it is always a fraction of what fits in a server.

You also lose the management side that a server takes for granted: the independent remote console that lets you power the machine up and diagnose it even when it is off is usually not there, and at a remote point that is exactly what you miss. You make up for it with other things —a relay that cuts the supply remotely, an automatic power-on when the electricity comes back— but it has to be designed in, it does not come as standard.

So the rule is a simple one: this is for where there is no reasonable alternative. If there is a room, power and somebody to maintain it, a real server gives you more for the same money. If there is none of that, this solves the problem and a server simply cannot be installed.

How many days of recording will really fit in there. A compact unit with solid-state memory holds very few days of several cameras: the sum is done just as it is anywhere else —bit rate per camera, hours, subtractions— and it nearly always forces you either to hang storage off it or to decide that only a few days are kept there and what matters goes up to the centre.

How you get to it. If there is no fibre, there will be a radio link or a mobile modem, and then you have to decide what travels over it: certainly not all the video, but alerts, images and whatever somebody asks to see. Access to administer it goes through a tunnel and never by opening a port to the internet.

What happens when the power goes and when it comes back. Running at low voltage it can hang off a supply with a battery, which at a remote point is simpler than a backup unit; and it has to start up on its own when the power returns, because nobody is going to go and switch it on.

And who is going to go out if it stops responding. That is the question that decides the design of a remote point: if the answer is «somebody in a fortnight», then you need to be able to restart it remotely, to be able to see why it went down, and to accept that for those two weeks that point is not recording.

As the central recorder of a large installation, no. With many cameras, people watching mosaics and a long recording period you need a server with bays, redundant power supplies and a remote console. Stretching a compact unit that far is saving on the worst possible part.

And we would not fit it for demanding analytics. There are units of this class that accept acceleration and can analyse a few cameras, and that is fine for what it is; but if what you need is to analyse many cameras or ask complex questions of the image, that calls for another machine and it gets said beforehand, not after twelve points have been installed.

The unit itself is administered like any small machine: updates, watching that it is alive and still recording, and an alert when it stops responding. IT handles that with their own tools, and it is as well that they do, because a remote point nobody watches stops recording and nobody will find out until somebody asks for a recording.

What has to be agreed is the access: through a tunnel, with the client's own credentials, and without exposing the unit to the internet. And an alert saying «this point has stopped recording» that reaches somebody who can do something. That matters more here than anywhere else on this list, because nobody walks past the machine.

Our side is the sizing and the site: measuring again if cameras are added to that point, checking that the cabinet temperature is still within the unit's range, and deciding when that point has grown so much that it now calls for a server. That happens more often than it seems: what started with four cameras has twelve three years later.