This section by Andreas Koch.

Just a short overview here, for a more detailed description (table), see
also 8.10 kinds of atari RAMdisks (and 8.11 + 8.12 for programs that
support or require a RAMdisk). The following memory enhancements do exist:
- Atari 400/800: RAMdisks on memory boards, that fit into the normal 
  Atari 800 memory slots (Axlon and Mosaic types);
- Atari XL/XE: a) internal memory enhancements: 
  - piggy-back versions,
  - professional PCB versions,
  - SIMM-module versions;
               b) external memory enhancements: 
  - via XL-Parallel-Bus, 
  - via XE-Cart.port+ECI, 
  - Flash-ROM cart. versions, 
  - other Cartridge versions, 
  - RAM-Card versions, 
  - SIO-cartridge versions, 
  - ...                
Note that many of these XL/XE memory enhancements are just hobbyist or
self-made projects. Most versions which use newer PC technologies
(Flash-ROM cart., RAM-Card, SIO-cart., etc.) are still under development!