Thanks for your input.
The cartridge is labeled E2PROM Storage Catrtidge. So I'm assuming it's writable. It won't insert backwards; that's in the design of the case. When I try to copy internals to it the keyboard tells me 'write failure : press any key to continue'...now I just have to find that 'any' key... :<{)

I checked the SD1 manual again aand it refers to a Stor-Cart...so maybe I've got something designed for an earlier product.
Thanks again.mn