From Forum Nokia Wiki

EPOC Kernel Architecture 1 (EKA1) is the first variant of Symbian OS kernel. It first appeared in 1997 as the kernel of EPOC32 OS in Psion’s Series 5 PDA. Symbian OS had EKA1 kernel till version 8.1a (S60 2nd Ed, FP3) when it was replaced with EPOC Kernel Architecture 2 (EKA2).