Model 100 RAM
Original
The original ram came in the form of 4 2Kx8 on a ceramic carrier module to make a single 8k chip, and up to 4 modules total may be installed for a total of 32k.
Each module still acted like 4 seperate 2k chips. The 2k chips are combined physically but not logically. There are 4 seperate chip-select lines for each module socket, and when ram is accessed, only one of the individual 2k chips is selected by it's own dedicated chip-select line.
| Radio Shack 26-3816 |  |
Replacement
Buy
Some new modules you may be able to buy. (stock comes and goes, people making and offering something come and go)
Francesco Messineo
GGLABS M10MEM
Build
You can always build your own.
This is a new design using all parts you can still buy new today.
https://github.com/bkw777/Model_T_RAM
| bkw777 Model_T_RAM |  |
Here are some other designs
Francesco Messineo
Stardust SMT
Stardust DIP
GGLABS M10MEM
Test
Hardware tester using arduino https://youtu.be/5fFRrfUjogs
BASIC software tester https://archive.org/download/M100SIG/M100SIG.zip/Lib-07-UTILITIES%2FRAMTST
Past 3rd party
There have been many 3rd party ram modules over the years. Here are just a few examples.
| NEC PWD-458 |  |
| Purple Computing 1983 |  |
| Purple Computing 1985 |  |
| C.I. 1984 (possibly Cryptronics?) |  |
Other
There are also ram expansion accessories that connect to the system bus and either add extra banks of 32k to the internal ram, or replace the internal ram. These aren't normal ram modules that plug into the normal ram sockets. They plug in to the system bus connector and provide the entire 32K address space at once from there, as if all ram sockets were filled.