After Effects RAM, disk, preview, nucleo

there are 2 differents levels of render in AE workflow (design choice)
1 - for viewing your comp, you need to make a preview
1-1 the ONLY realtime preview avaible, is RAM preview. Disk preview is almost never realtime !
2 - for exporting your comp as a footage (final file), you have to render AGAIN
no preview here, it's a simple transcoding process like premiere export.
there are 4 channels per pixel RVB + alpha
AE cs4 is still a 32 bits product, so you CAN'T have more than 4GB for the main instance, even in 64bits OS with 16GB RAM and 8 cores.
max ram avaible for preview		3	GB	(maximum RAM Cache size in preferences menu)
ram used per frame		MB	frames avaible for preview	time available in NTSC (sec)	time available in PAL (sec)
SD full D1	8bpc	1,33	2301	76,7	92,1
	16bpc	2,67	1151	38,4	46,0
	32bpc	5,34	575	19,2	23,0
HD full 1080i60	8bpc	7,91	388	12,9	15,5
	16bpc	15,82	194	6,5	7,8
	32bpc	31,64	97	3,2	3,9
so… that means, you CAN'T get more than 7 sec realtime preview of your composition !
if you want to see more, you have to select another start time in your time line, wait for a RAM preview render, and see again a little 7sec.
it's not a joke.
how works the disk cache ?
is there a way to render all the work area by using disk cache ? And when i hit "preview", the RAM preview is used as a buffer filled up by disk reading ?
it will be like a "disk preview" ? Instead of wasting 3GB RAM for storing the preview, take 1GB and give 2GB to be allocated to ram for rendering.