There are SRAM ICs / boards, however, don't expect 100 MB, more like 1 MB (with the pin numbers and connectivity / protocols that an Arduino offers).
With Flash you can get much further, but it can only be written a number of times; not sure if that suits your requirements.
Beyond that, I'm afraid the real problem is in the processing speed. Mixing 100 ...
You have ATmega328P-AU. Classic Uno with DIP socket has ATmega328P-PU. Arduino Uno SMD has Atmega328P-MU.
The automotive versions ATmega328P-15AZ and ATmega328P-15MZ have separate datasheet starting in Revision History with
Creation of the automotive version starting from industrial version
based on the ATmega48P/88P/168P/328P datasheet 8025F-AVR-08/08....
You need a programmer to burn fuses. If you have another arduino then you can use the Arduino as ISP example sketch in the IDE. You can't burn fuses just using the USB cable like you upload code with. The only reason that can talk to the chip at all is because there is another chip to convert it to serial and a bootloader on the 328P to allow it to upload ...
1KB is 1024 bytes, not 1000 bytes.
Therefore 32kb = 32768 bytes.
32768-512=32256, which is exactly the value used for upload.maximum_size for the 328p.
4kb=4096 bytes. 32768-4096=28672 which is the value for the 32u4.
I'd also suggest looking into different microprocessors. The Teensy models often have an SD card socket, and the Teensy 4 (especially if they release one with a built-in SD socket) is extremely fast and capable (600MHZ, dual instructions/cycle). That would be far better suited than an Arduino, though you'll still have RAM limits. (Nowhere near 200 megs, but ...
You can temporarily put it in an UNO. Don't connect this UNO via USB, but use jumper wires to connect the ISP pins plus the power pins to the other Arduino that you are using as an ISP programmer. (You could also use the (2x3) ISP header on the UNO if that's more convenient.)
Or, you could use a high voltage programmer.
Or get/desolder a crystal from some ...
The answer i've accepted is the proper answer for the problem i asked.
However replacing the C runtime requires to attach and maintain a lot of crt.S files oiginally related to the GCC. To avoid this i "slept several times over this prolem" and came out another solution.
After compiling the host application that have to redirect the interrupt calls