I upgraded one of my spare Amstrad CPC464 machines to the same specification as the CPC6128. I have been wanting to do this for years! There are 3 things you need to do to upgrade your CPC464.
1. Replace the OS and BASIC ROM. I took the OS and BASIC ROM files from the WinAPE emulator ROM folder. There is only 1 ROM chip in the 464, so you have to merge the OS and BASIC rom files together. I used the following MS-DOS command to merge the files. You can use the cat command in linux to merge files too.
copy /b OS.ROM+BASIC.ROM 6128.ROM
Once you have the ROM file, burn this to a 27(C)256 EPROM. I removed the original ROM chip, put in a IC socket and them popped in the EPROM.
2. Add and additional 64k RAM. I had a dk’tronics 64K RAM pack. If you are luckly enough to have a RAM pack that has the removable RAM chips, you can upgrade it to 256K.
3. Add a disk drive. Either a 3″ or 3.5″ drive via a DDI-1 disk interface.
Thats it – my CPC464 now works like a CPC6128. It even has the same startup information page. It will say 128k even if you dont have the RAM pack attached. The 128k text is hard coded into the OS ROM.