CMS 512MB (1X512MB) DDR1 2100 266MHZ ECC Registered DIMM Memory Ram Upgrade Compatible with Cisco® 2811 Router Main Memory DMemory Ram Upgrade2811-512D for Server Only - C89 at Amazon.com
Desktop PC / Computer, Laptop and Server Memory / RAM DDR1 DDR2 DDR3 SDRAM, Interface Speed: PC3200