For 32 bit ARM, it seems to be shortcuts in the SoC design a.k.a there's a reason some boards cost under $50.
There exist some designs with real SATA (eg. Cubietruck) but those have poor CPUs (A7), and there exist many designs with SATA-via-USB which is never going to be fast. Also micro SD cards have abysmal performance for the sort of random I/O that operating system root filesystems have.
Luckily the situation in 64 bit ARM server land is much better. The APM Mustang and AMD designs have a combination of fast cores and properly engineered I/O subsystems. Real SATA, multiple 10gigE and 1gigE interfaces, PCIe, etc.
I would say it is not so much shortcuts as the fact that the 32-bit SoCs are generally designed for mobile. The only way to get a cheap devboard is to use an SoC which is being produced in high volume, so it doesn't have a prohibitive cost. That means you get the peripherals that a mobile phone or tablet wants, and not the ones that it doesn't, typically. If you insist on using an SoC custom designed for a devboard then the board is probably going to be tens of thousands of dollars.
64-bit is better because there are SoCs directly targeting server usecases which therefore have the kind of peripherals you'd prefer to see in devboards.
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For 32 bit ARM, it seems to be shortcuts in the SoC design a.k.a there's a reason some boards cost under $50.
There exist some designs with real SATA (eg. Cubietruck) but those have poor CPUs (A7), and there exist many designs with SATA-via-USB which is never going to be fast. Also micro SD cards have abysmal performance for the sort of random I/O that operating system root filesystems have.
Luckily the situation in 64 bit ARM server land is much better. The APM Mustang and AMD designs have a combination of fast cores and properly engineered I/O subsystems. Real SATA, multiple 10gigE and 1gigE interfaces, PCIe, etc.
I would say it is not so much shortcuts as the fact that the 32-bit SoCs are generally designed for mobile. The only way to get a cheap devboard is to use an SoC which is being produced in high volume, so it doesn't have a prohibitive cost. That means you get the peripherals that a mobile phone or tablet wants, and not the ones that it doesn't, typically. If you insist on using an SoC custom designed for a devboard then the board is probably going to be tens of thousands of dollars.
64-bit is better because there are SoCs directly targeting server usecases which therefore have the kind of peripherals you'd prefer to see in devboards.