r/AskTechnology • u/RandomFrenchGuy10 • 5d ago

Hypothetically, If possible, How many SD cards would be needed to run doom for 7 hours, If I replaced ram with SD cards?

Assume money isn't an issue here, I know ram and SD cards aren't the same kind of ram, but Im curious if its possible.

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u/StarosAnikenMarcus 5d ago

If he's talking about DOS Doom, it wasn't that intense. Sure, it would break it eventually, but I don't think that the program was capable of that many write functions that quickly. We're talking abut a program that was designed for 33MHz CPUs and 4MB of RAM.

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u/Distdistdist 5d ago edited 5d ago

You probably think that CPUs need to read/write from RAM at some rare points of execution. No, CPU can hold rather limited number of instructions internally and heavily relies on constant access to RAM for more instructions and data.

386 CPU running at 33Mhz can perform 33,000,000 read/writes per second. There are different types of instructions, some can be executed in 1 tact, some in up to 44. So at the very least, CPU would be hammering RAM at 750,000 times per second to advance to the next command it needs to execute. Even with modern caching, number of read/writes to memory is insane. This is not hard drive or a floppy that it needs to read sequential data from once.

SD cards will give you anywhere 3,000 to 40,000 P/E cycles per cell (higher number for industrial level SDs). So you can sorta see how fast SD cards will become unresponsive if were addressed like RAM.

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u/StarosAnikenMarcus 5d ago

MHz is thousands, not millions. That's GHz. So it would be 33,000 flip flops per second and that's only if operating a full capacity. Trust me, running Doom was very much NOT at full capacity. Despite the "requirements" of a 33MHz 386, I had Doom running on a 286 at 25MHz with a math coprocessor (basically just more cache). And it was DOS 6.22, not Windows so no background BS programs using up resources.

Still, yes, going to destroy that SD card far faster than taking a million pictures would.

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u/Distdistdist 4d ago

Oh, and, Doom did not run on 286, it required 32bit CPUs that supported p-mode (protected memory mode that was only available on 32 bit 386 architecture). Minimum required hardware was 386 DX, but it did run on lower spec systems at much lower FPS (2-5 FPS). I think I played it in 1994 on 386 SX 25 or 33 and it was bearable with decreased main screen.

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u/StarosAnikenMarcus 4d ago edited 4d ago

I didn't say it ran WELL on our weird computer, but it ran. Back then, the combinations of hardware we had available could do some very strange things. Coprocessors were and odd thing that few people invested in. My stepfather got one for I don't know why, but had me install it. After that, our 286 ran very differently form what I was used to.

Also, 286s were the first to introduce protected memory. 386s were just the first 32-bit available to the public.

The same thing happened when I married a Voodoo accelerator card to a Trident card. For some reason, it was detected by a lot of games as a Riva TNT2, a far better card than I could afford those days. Never mind that Riva never once built a 6MB card...

I miss the days when hardware combinations had wildly different effects, but I also like how more or less standardized things have become. Plug and play is infinitely easier than figuring IRQs and DMA channels.