I upgraded my ER1401 with a matched pair of SODIMMs, so I have the original one removed.
Using this to upgrade your ER1401 or ER1402 will improve performance.
First use a free program you check what part number is installed in yours currently. You can get information on your currently installed ram with a program called cpu-z (http://www.cpuid.com/softwares/cpu-z.html) on the SPD tab, this will give the part and serial number of the installed SODIMM.
2GB 2Rx8 PC3-10600S-09-10-F2
£12 includes delivery costs