When you use the tool ACATune 1.7 with the command acatune -maxmem, you get the rest of the memory. You than have a total of 12 MB of RAM. 1 MB is reserved as Mapping Kickstart ROM.
Maxmem bit: 0xb8f034
This bit is reset after every system reset. While this bit is reset, the following address spaces are mapped to fastmem:
0x20.0000 to 0x5f.ffff (4M using autoconfig™)
0x60.0000 to 0x9f.ffff (4M)
0xc0.0000 to 0xcf.ffff (1M will be added by all Kickstart ROMs)
0xde.8000 to 0xde.ffff (32k as buffer mem and trampoline code area)
All other addresses will access the A600 mainboard, where the usual Amiga memory map applies.
It is not recommended to add the 32k space at 0xde.8000 to the freemem list.
While this bit is set to 1, the following spaces are mapped to fastmem (in addition to the above spaces): 0xd0.0000 to 0xd7.ffff (512k)0xa8.0000 to 0xb7.ffff (1M)
0xea.0000 to 0xf7.ffff (896k) The Maxmem bit can be set and reset at any time. While reset, the contents of the unmapped memory areas stay unchanged and survive a system reset. Which by my maths makes it 11.375mb, so nobody is advertising it correctly. But then you can do some funky things to use even more ram, but not in a way that you can call AllocMem() and get it
Special memory mapping If the Maxmem bit is reset, but the expansion ROM protect bit is set, the memory areafrom 0x40.0000 to 0x7f.ffff will contain the memory areas that would normally be
unavailable due to IO and chipmem areas covering this memory. In order to make almost
all physical memory available to special software, this bit setting will move:
0x00.0000-0x0f.ffff to 0x40.0000-0x4f.ffff
This Fastram area is normally covered by the lower 1MByte of chipmem. Caution: This
includes lowest 4k that is used by the IRQovl function. Make sure that your software does
not accidentally overwrite this memory area, as it contains all CPU vectors in case that
VBR is 0.
0xd0.0000-0xdf.ffff to 0x50.0000-0x5f.ffff
The lower half of this area is available with the Maxmem option, and the upper half from
0xd8.0000 and higher is normally covered by IDE, RTC and chip registers. Caution: This
Inside Amiga Classic Accelerator 620 Page 5
also includes the 32k area from 0xde.8000 that is always visible. Make sure that your
software does not accidentally overwrite this memory area, as it might be used as a jumptarget
for Level-7 IRQs.
0xa0.0000-0xaf.ffff to 0x60.0000-0x6f.ffff
The upper half of this fastmem area is available with the Maxmem option, and the lower
half is normally covered by PCMCIA/Gayle registers.
0xb0.0000-0xbf.ffff to 0x70.0000-0x7f.ffff
The lower half of this fastmem area is available with the Maxmem option, and the upper half is normally covered by CIA registers and the ACA620 registers. Alltogether, this option lets you use the hidden 2.5MByte of the physical memory, for example for a reset-proof RAM disk.
I assume that this board prevents you from using some or maybe all PCMCIA cards, not that many people will care.It'll be interesting to see if the hidden 2.5mb of ram can ever be used for anything. There is something in the docs about another mode that is designed for a freezer type mode (like action replay). Without either software you only have access to the standard extra ram & the 1mb of mapped rom.
Source: http://eab.abime.net/showpost.php?p=844037&postcount=242