Apple doesn't release how much memory their iOS devices have as a tech spec. The best we can do is find out by debug messages (like you just linked) or physically examining the device (ifixit).

Apple would say it has "enough" RAM. I thought that one of the game demos mentioned that it had more resources than an Xbox 360 or PS3, but I don't think they were talking about RAM.

IIRC the PS3 has 256mb of ram.

256 MB of XDR (for the Cell BE) and 256 MB of some kind of DDR (for the RSX).

The comparison to the amount of RAM in TF101 doesn't make any sense. It runs different software.

It all runs different software, but games are generally going to use the same amount of data.

Generally? Does MW3 uses same amount of data on PS (256MB + 256MB), XBox(512MB), Wii (88MB) and PC (2GB required)?

I did a test a 1024x768 PNG vs the Same PNG at 2048x1536. 299k vs 664k. So for raster images it more than doubles the footprint, however if you use vector assets there should be little impact.

After decompression into memory, that 2048x1536 image will take exactly four times the memory as a 1024x768 image.

But you don't store compressed PNGs in RAM for display by the GPU. Does the GPU even support lossless texture compression? I would imagine it supports lossy texture compression.

Edit: It is also interesting to see that the ~ 2x increase in the size of the PNG can be explained by PNG's run length encoding. When you double the pixels in each direction, RLE should readily compress the horizontal pixel replication but not the vertical pixel replication.

It seems Apple uses a "modified" png standard for iOS (enabled by default) that compresses the images even more when they are added to the App Bundle. http://iphonedevwiki.net/index.php/CgBI_file_format#Decoding

True, though as jevinskie says, we're not talking here about the way images are stored on disk but about what needs to go in the GPU memory.

Totally understood, and I'm well aware of the increased memory footprint required once they are uncompressed. Way back in 08 when I was working on my first iPhone app you had to be very careful with memory a small animation with 120 images of 50k each could quickly max out the 50mb of usable memory the iPhone 3G had unless you cashed properly and released assets as soon as they were not in use. I should have been more specific in my original post.

Yeah, iOS device GPUs support lossy texture compression in the form of PVRTC. There's no lossless texture compression support, as far as I know. (I'm talking in-memory here, obviously, not on disk as PNG or JPEG or whatever else.)