While desinging adesigning an MCU, you have to face conditions, which are not that important inon PCs.
Durability
To choose the components, you don't neccessarily take the best or/and most performanthigh performance parts, but those that have proofenproven to run proper after several years of usage, will be availible inavailable for several years and are capable to runrunning 24/7 for years. Due Due to this cirtumstatecircumstance, if a controller is on market for several years, doing its job fine, it seems to have poor ramRAM, compared with the PC standartstandard today. But anyway, it does its job fine, and there should be no need for replacement, if the engineering was well.
Space Microprocessorunit
Microprocessor units literally are micromicros. You have to cut down needetthe needed space to the absolute minimum. Of course, you can get a 256mb256 MB at the same space as 10years old 64kb10-years-old 64 KB chips, this. This is where #1 comes to point.
Price
Not only the purchase price, but also the power consumption, you. You don't want to design aan MCU that has controllcontrol over aan entry-system, that needs 1000W1000 W, if your rival in business has one that only needs 25W25 W. And of course, cheaper purchase price (at the same quality) is always better.