Kaspersky has recently launched a free version of their AV & it is quite good(especially with RAM & runs quite light). On my system though it reduced my downloading/uploading speed so I uninstalled it but it maybe because my OS install is quite old(~6.5 years) with some old issues.
Avira free is also very good or you can use Avast free(do configure it properly though for maximum protection & minimum resource usage).
Avira free is also very good or you can use Avast free(do configure it properly though for maximum protection & minimum resource usage).