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The maybe most distinguishing feature of a "mainframe" is intelligent I/O channels, which offloads a lot of what would otherwise be CPU work. And those I/O chan
by Tor3 4y ago
The maybe most distinguishing feature of a "mainframe" is intelligent I/O channels, which offloads a lot of what would otherwise be CPU work. And those I/O channels is why the PDP-10 was called a "mainframe" while the rest of the PDP series (without I/O channels) were called "minicomputers".
There's more, but it depends on the system - some can do maintenance on parts of the system while still operating.
- HyperSane 4y agoThe x86 world is getting I/O channels in the form of "SmartNICs" which are NICs with substantial processing power.
- rbanffy 4y agoThey also have it with disks local and remote. The idea is that the CPU is running user code 100% of the time and that it doesn’t need to wait for anything.
- neverartful 4y agoWith the mainframe all disks are external. This diagram [0] does a good job of showing that. [0] https://en.wikipedia.org/wiki/Count_key_data#/media/File:IBM_CKD_Arch.png https://en.wikipedia.org/wiki/Count_key_data#/media/File:IBM...
- HyperSane 4y agoMost enterprise servers use external storage arrays.
- trasz 4y agoIn the PC world this has been done couple of times, eg https://en.m.wikipedia.org/wiki/I2O https://en.m.wikipedia.org/wiki/I2O from the late 90’s. I think the real reason why it works for mainframes is that their operating system is so primitive, so it’s easy to cross layers - because there are so few of them. z/OS is closer to MS-DOS than to Unix in that regard.
- Sebb767 4y ago> some can do maintenance on parts of the system while still operating. That's not that rare these days. Basically any server will allow hot-plugging hard drives, with some configurations network cards and by now a lot of laptops can even hot-plug GPUs via Thunderbolt.
- deleted 4y ago[deleted]
- rbanffy 4y agoI remember some big iron could do it with processors and memory as well. IIRC, you can no longer remove CPUs with IBMs, but replacing memory is relatively simple.
- neverartful 4y agoHot-plugging hard drives is a bare minimum. There are many other points of failure and a failure of any of the following WILL result in downtime while the component is replaced: disk controller, CPU, memory, NIC. Having dual NICs and dual processors helps, but it's still a far cry from 100% availability.