Arguments for DiskRAM
From PEL Wiki
This page is supposed to be a repository for the machinations leading to an effective argument for DiskRAM. Even though it makes lots of sense to me, I need to be able to evangelize effectively.
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Historical Argument
Historical Argument argues that storage belongs in the memory hierarchy, and is not there only because of a historical lack of address space.
Makes Sense Argument
Makes Sense Argument is very closely related to Historical Argument, but instead of claiming "That's the way it was", I claim that it is the way it should be. Hard drives are not I/O. They are an integral part of computer, in terms of storage, and therefore belong in the memory hierarchy. The most obvious comparison is the comparison with tape backup.
Efficiency Argument
Efficiency Argument goes through the steps necessary for swapping and compares it to a caching memory hierarchy. It could also address filesystems. It then takes that a step farther and asks what we would do differently assuming the new cost structure. It also addresses the reformatting necessary to write information to files which would not be needed if memory were persistent.
Information Argument
Information Argument assumes that we keep swapping and argues for more usage information to be collected. The only way to collect more is in hardware without high overheads. Once you have this infrastructure, it's cheap to add the rest of DiskRAM.
Large Main Memory Argument
Large Main Memory Argument assumes that everyone wants 1TB of DRAM, but can't afford it. DiskRAM falls out of that.
Disk = cheap & persistent Memory = fast & simple DiskRAM = cheap & persistent & fast & simple
I include the Letter From Chris Wanner at HP for a reference. In brief, he says that the reason that Disks are not part of the memory hierarchy is that they are so much slower. The latency would tank performance. That made me wonder if DiskRAM would overload the queues on the bus. In other words, would the slow transactions tie up the bus so long that the processor couldn't continue? Wouldn't it be the same as it is right now? Why, or why not?
Categories: Pel | Myles
