FM Towns:Upgrading RAM

FM Towns uses non-parity SIMM RAM from the same era. Generally, it's very cheap and available to buy on the net.
It has been tested extensively that with tower models when placing more than 8MB of RAM games start to hang and have long load times.
For example, CX20 with ODE takes 2+ minutes to load a game to the menu when the CX20 has 26MB RAM (maximum).
The maximum amount of RAM any retail game uses on FM Towns is 8MB. However, most games requiring 8MB of RAM also require a 486DX2 CPU.
For most models, 8MB or less is fine. There is a specific dungeon crawler game that crashes and refuses to load if more than 8MB of RAM is present.
Therefore 8MB is a good amount for towers.

FM Towns performs a RAM count on powerup counting down the RAM in the computer which is present. This is helpful for the next section.

Adding RAM

Notice the Red Boxes. This is where jumpers must be manipulated to tell the computer how much RAM is present.

FM Towns has SIMM RAM slots easily accessible to the end-user when the primary cover is removed.
Refer to the Models page to determine the maximum amount of RAM that can fit in each slot in the computer.
New RAM must follow these timing specifications.

Model type	RAM access time in nanoseconds
HR and Towers	100ns or less
ME/MF/Fresh/Fresh TV	80ns or less
MA/MX	80ns or less
EA	60ns or less
HA/HB/HC	60ns or less

Each SIMM RAM stick will have jumpers present on them. Entry-level soldering can be performed to change these jumpers.
SIMM identification isn't universal for everything and you might have to manipulate the jumpers in a few ways until you're satisfied.
Basically, opening and closing jumpers until the memory present from the memory count on the computer satisfies you.