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Old 14 November 2017, 13:49   #1
Nightfox
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Virtual Memory on Amiga?

I was thinking, since the 68010 and above support virtual memory, was this ever used on the Amiga? Seems like a handy way to get extra memory in Workbench, albeit it would be slow.
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Old 14 November 2017, 13:59   #2
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yup, there's some extensions for it; VMEM and GIGAMEM. You do however need a full Paged MMU for this to work (so practically a full 030/040/060).
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Old 14 November 2017, 14:03   #3
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Is it too slow to be practical?
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Old 14 November 2017, 22:59   #4
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I can't speak for VMEM as I've never used it, I did use Gigamem on my A1200 with a Blizzard 1230IV for a while and didn't notice any slowdowns, the 030 on that card has a full MMU.
You can only use FFS though, it won't patch any other filesystem which is a let down for me, and the reason I stopped using it, I use PFS3 for the larger partition size.
It would be a great solution if it supported any Filesystem, but as it is very limiting!
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Old 15 November 2017, 12:09   #5
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As opposed to other systems, the Amiga virtual memory solutions only swap pages to the hard drive when free RAM is critically low. So you won't get a slowdown until it's actually using the swap. When it does though, it will be quite slow - especially on a slow interface like the built-in IDE.
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Old 15 November 2017, 14:30   #6
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Yeah I failed to mention that when I used Gigamem I had a external SCSI drive connected to the Blizzards SCSI kit dedicated for swap. Never tried it off the IDE port but can imagine it would slow it down a little.
Even so, as long as you are only using FastFileSystem it is a useful addition for extending RAM support.
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Old 04 December 2017, 04:49   #7
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@ptyerman

Hm, I always used a dedicated partition for swap, and it was not dependant on any particular filesystem - are you sure you're not confusing with MuFS?
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Old 04 December 2017, 05:19   #8
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Nope. As already stated GigaMEM will only use FFS, it won't patch any other filesystem. Its in the documentation if you want to have a browse of it.
I can't speak for any other implementation as I only ever tried GigaMEM.
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Old 13 October 2019, 17:22   #9
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I don't think any 68010 implementation on the Amiga ever came with a general purpose MMU, and I don't think any software on the Amiga supports the 68451 MMU (which is what would work with the 68010) anyway.

A few 68020 cards like the official Commodore A2620 did come with the 68851 MMU, and some software does support it, but these cards are relatively rare.
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Old 13 October 2019, 19:22   #10
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GigaMem is great if you know how and when to use it.

It allows you to configure under which conditions should virtual memory kick in, and this is great for running some applications that require a lot of memory you won't be having anytime soon, like for example editing a huge picture with ImageFX.
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