Editing Atari 600XL Troubleshooting Guide (section)

=== Compatible DRAM Replacements ===
The following DRAM types are confirmed compatible with the 600XL:
* '''4164''' (direct replacement) — µPD4164, HM4864, KM4164, TMS4164, MB8264, MT4264
* '''4264''' (backward compatible with 4164)
* '''41256''' (will function at 64K density, operates as a drop-in for 4164)
* '''4464''' (for 64 KB upgrades, requires wiring modification)

Speed ratings of -10 (100ns), -15 (150ns), or -20 (200ns) are all suitable. Mixed speed ratings on the same board will function correctly, with all chips operating at the speed of the slowest IC.