Old school Manframes have poor IO by today's standards as in less than a mid range wireless access point. And, the software and hardware where ridiculously stable by today's standards but, if you look at mean time between failures in therms of operations preformed not just time they once again fall behind.
PS: Still, to give an idea of why Manframes where considered such IO beasts a high end PC's IO is about ~1000x as fast (HDMI is 10.2 Gbit/s + USB + Gigabit Ethernet etc), but it's got ~1,000,000x the processing power.
Of course, if you don't pretend that mainframes stopped advancing, you see a different picture. Modern zSeries (or whatever new marketing they've come up with) have multiple 10Gbit interfaces to a network, and can keep them all fed. Not to mention special offload processors for AES and X509 certs, and of course hardware partitioning and virtualization built in. Mainframes are still pretty badass - a lot of stuff that is exciting and new in the server space is stuff that IBM was doing for decades in the Mainframe space.
There is just something very cool about handling something on the order of 10^5 fully ACID transactions per second, while still allowing real time database querying and on-the-fly hardware failure tolerance.
Mainframes are obsolete systems which decades ago all the worlds infrastructure relied on, today they are obsolete systems that all the worlds infrastructure relies on and tomorrow they will be ....
Yeah, but SD cards also have horrible IO by today's standards and they're commonly used for little boards like this.
Up to 4x I/O channels running at 3MB/second for the mainframe would be considered pretty good for small (4 kiB to 16 kiB) file operations on almost all microSD cards today.
PS: Still, to give an idea of why Manframes where considered such IO beasts a high end PC's IO is about ~1000x as fast (HDMI is 10.2 Gbit/s + USB + Gigabit Ethernet etc), but it's got ~1,000,000x the processing power.