The 16K TS1016 and the ZX81 16K RAM Packs disable the internal memory on the TS1000/ZX81 as said by KWF.
On the TS1500, it does not disable the intermal memory, it moves the internal memory do the 32K-48K windows and maps itself on the 16K-32K window.
The ZX80 1-3K RAM Pack also does not disable internal RAM, it adds RAM to the internal memory map and can have 1K, 2K or 3K RAM taking the machine to a wopping 4K RAM! Not sure if it only works with the ZX80 or if it also works with the ZX81...