Cisco 12000 Series Internet Router Architecture: Memory Details - Cisco
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
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