Hi Malik,
From this FAQ:
http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_qas0900aecd80169bd6.html
Default memory
Cisco 2800 uses external compact flash memory; Cisco 2801 uses non-error correction code (ECC) synchronous dynamic RAM (SDRAM), and Cisco 2811, 2821, and 2851 use Double Data Rate (DDR) ECC SDRAM
2801
Default and maximum:
• 64/128-MB compact flash memory
• 128/384-MB SDRAM
2811
Default and maximum:
• 64/256-MB compact flash memory
• 256/768-MB DDR SDRAM with ECC
2821
Default and maximum:
• 64/256-MB compact flash memory
• 256-MB and 1-GB DDR SDRAM with ECC
2851
Default and maximum:
• 64/256-MB compact flash memory
• 256-MB and 1-GB DDR SDRAM with ECC
Looks like for above a 2801 the maximum is 256 MB.
hth,
nick
