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--- sd:256k_vs_512k [2026/04/26 04:37] – created appledog
+++ sd:256k_vs_512k [2026/04/26 04:49] (current) – appledog
@@ Line 11: / Line 11: @@
 There just wouldn't be enough space in memory to hold the assets, and pulling it in from OPFS would be very expensive. Not like reading data from a cartridge.
-__2. Twice the speed, twice the RAM__\\ The truth is, we're not just twice as fast as a C128, or four times faster than a C64; we're about ten to twenty times faster. The reason is that there is almost no register pressure here, and we have a PPU like 80s era consoles did. Therefore to make use of this speed, as restrained as it is, we are going to need more ram. Here's a chart explaining the issue by comparing our memory map to various retro-era consoles:
+__2. Twice the speed, twice the RAM__\\ The truth is, we're not just twice as fast as a C128, or four times faster than a C64; we're about ten times faster. The reason is that there is almost no register pressure here, and we have a PPU like 80s era consoles did. Therefore to make use of this speed, we are going to need more ram. Here's a chart explaining the issue by comparing our memory map to various retro-era consoles:
 ^  ^ NES ^ SNES ^ TurboGrafix-16 ^ SEGA Genesis ^ Neo Geo ^ GBA ^ SD-8516 ^
-| RAM | 2k | 128k | 8k | 64k | 64k | 288k | 64k |
+| RAM | 2k | 128k | 8k | 64k | 64k | 288k | 128k |
 | Video | 2k | 64k | 64k | 64k | 68k | 96k | 64k |
 | Audio | n/a | 64k | n/a | 8k | 2k | n/a | 64k |
 | Total | 4k | 256k | 72k | 136k | 142k | 384k | 256k |
+The SD-8516 has 64k free in each of Bank 0, 2 and 3. Bank 1 is reserved for the operating system -- technically you can use that space, but it is not recommended. You can also use parts of bank 2 depending on the graphics mode. It's not used in modes 1, 2 or 6. Then there is bank 3, which can also be used for RAM. But if you do that, then you wont't have any audio memory.
+So while we are comparable to many of the era's consoles, we should have at least enough RAM to compare with some of the cartridges. That is the problem; we didn't account for cartridges.
+== What's in a Cartridge?
+A lot of SNES and other cartridges came with extra RAM, APUs, and so on. This all strongly suggests that the system memory here should be more likely 512k or even 1 MB. This would put us squarely between the SNES and the N64, which is actually probably a good place.
+For now, i'm just thinking about it. But if I do decide to increase ram, it will be to 512 first. The Amiga 500 came with 512k RAM. You could do a lot with that, you could probably cache enough assets to run most SNES games. The issue is I don't want to give the system too much memory or it might lose it's retro feel. Maybe we can slowly increase the RAM by just 1 or 2 banks and see how it works out.