A completely unquantized fp16 model weight 7B LLM is about 15GB on a disk. You need closer to 24GB of memory for inference with a decently sized context.

Quantization is black magic of the software variety that seems to be able to significantly reduce that without a commensurate loss in quality, though the results are a little subjective. Some well reviewed quantizations of 7B models can get them below 9GB.