Changes

Bits 3, 4, 5 allow to define up to 8 pages of 64K for RAM expansion at a given address range. This does not affect in addition to the 64K base RAM. The internal second 64K RAM bank of the CPC 6128 is usually disabled when a RAM expansion is used, as the 64K enhanced RAM in the 6128 would use the same address range (&7Fxx) as the first 64K of the RAM expansion. This gives you 576K of total RAM on a CPC.

The internal RAM of the CPC 6128 adds 1x 64K, which is usually disabled by expansions, because at the same address range (&7Fxx). ButHowever, if the expansion RAM expansion decodes the [[Standard_Memory_Expansions#Extended_1M-4M_Expansions_.28RAM7.2FYarek-style.29|A8 address line]], you can still access this page the internal second RAM bank of the 6128 from another range (&7Exx), like . The [[X-MEM]] expansion doesand [[CPC_iRAM#CPC_iRAM.2F640|iRAM/640]] expansions implement this and therefore can provide 640K of total RAM. [https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/extram-512kb-to-640kb-for-cpc6128-on-one-dip20-chip-slg46533v-dip/msg247763/#msg247763 Source]