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Modern CPUs can have L3 cache in the range of tens of megabytes (e.g. 24MB). W98SE requires at least 16MB of RAM to run (24MB recommended). Is it possible to use the L3 cache as RAM, without any external RAM attached?

SoniEx2
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2 Answers2

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Simply put, no.

While your CPU may have that L1/2/3 cache available, your OS will expect it to be used only for the CPU. The OS is going to want actual memory, in the form of RAM.

If you are gung-ho about using Windows 98, do yourself two favours:

  1. Get Windows 98 SE - it works much nicer in my experience
  2. Run it in a Virtual Machine. Virtualbox is free, open source, and available on almost every major platform.
Canadian Luke
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  • There isn't a tag for Windows 98 SE in case you didn't know. And I mentioned Windows 98 SE both in the post and in the title. – SoniEx2 Jan 13 '16 at 02:10
  • Correct answer, but wrong reason. Twice you mention the OS, but that is not the issue. If the OS *"expected"* something or is *"going to want"* something, then since the OS is software. the OS could be rewritten to expect or want an alternative. Rather it's a hardware implementation that dedicates the CPU cache as a cache rather than *byte addressable*, random access memory. – sawdust Jan 13 '16 at 03:27
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No. Motherboards require memory to function. Cache memory cannot be used as RAM.

Keltari
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  • Good point about motherboards requiring memory to function... But that's not the CPU. – SoniEx2 Jan 13 '16 at 02:15
  • Actually it's the CPU that requires memory. The RAM has to exist for the CPU; it doesn't matter where it's installed. If you consider something not x86, there are SBCs that have no memory chips because the RAM is integrated with the CPU in one IC package. Your third sentence is the correct reason. – sawdust Jan 13 '16 at 03:31
  • Do you have any proof that x86 cache cannot, under any circumstances, be used as RAM? – SoniEx2 Jan 13 '16 at 12:54
  • @SoniEx2 yes. basic computer architecture. – Keltari Jan 13 '16 at 16:54
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    Cache **can be used as RAM** on x86 and many architectures: [Cache-as-Ram (no fill mode) Executable Code](https://stackoverflow.com/q/27699197/995714), [CAR: Using Cache as RAM in LinuxBIOS](https://www.coreboot.org/data/yhlu/cache_as_ram_lb_09142006.pdf), [A Framework for Using Processor Cache as RAM (CAR)](https://www.coreboot.org/images/6/6c/LBCar.pdf) – phuclv May 07 '21 at 00:50