All stock Archos Recorders have 2MB of RAM (working memory, if I can say so in English...) and the DeviceChart just shows that. You can only have "8MB memory" (RAM) if you have done a hardware mod or got a modded model.
The builds for the standard memory size will always work but will give you less runtime in case you have such a modded Recorder because the disk has to spin more often to refill the buffer. The 8MB builds will crash on a standard Recorder - similar to the Ipod Video with 32MB or 64MB RAM.