ASICs are application specific integrated circuits. The most commonly known ASIC would be a bitcoin miner. An ASIC is a computer chip that does exactly one job, but it does that job with extreme efficiency in terms of speed, power usage, work done per unit of heat output, and physical size. This mod applies that concept to Factorio by allowing Megabases to continue to grow by consolidating some of the most entity intensive manufacturing processes into monolithic buildings.

All recipes take one second, and do not benefit from any modules or beacon effects. The bonuses from things like speed and productivity modules are baked into the recipes. The overall balance of the mod is that it takes just as many resources to build an ASIF as you'd need to build the same thing in a vanilla factory, and the ASIF produces (within rounding errors) the same volume of outputs for inputs as a normal vanilla factory would (not true for modules though; they benefit from productivity effects where vanilla wouldn't allow). In this way, mining and smelting remain a logistical challenge, and all you really gain is a (huge) UPS saving by consolidating (in the case of 25:1 green circuits) over 550 entities (assemblers + beacons + inserters + chests) into one. The UPS savings get even more extreme with red/blue or even module ASIFs.

The mod works by starting with the desired output ratio. Say you want one Green Circuit ASIF building to have the equivalent output of 25 beaconed and moduled Assembler 3s. (Mod settings allow this to be customized). The mod would then unroll the build chain back to base items (copper plate, iron plate, plastic bars, sulfuric acid, steel) and then determine how many assemblers and beacons would be needed to build that blueprint in vanilla factorio.

That determines the power draw, pollution, and size of the final building. If you changed from a 25:1 to 50:1 ratio, the building would double in size, but so would the power draw, output quantity, and materials need. As can be seen in the Speed Module 3 image, a zoom mod is highly recommended in conjunction with this mod as some recipes can be absolutely massive.

The main challenge in this mod is keeping the buildings fed. For example, to build Green Circuits at a ratio of 25:1, you need to get 400 iron plate and 428 copper plate into the ASIF per second. That means you'll need around 30 inserters just to load all the materials, and another 20 or so to unload the finished circuits.

The mod does feature a setting to constrain the maximum size of ASIF buildings, as they can become nearly impossible, if not actually impossible, to place down at higher ratios.