. you upgraded the cisco ios feature set or release and it requires additional sdram.
. the router maintains large routing tables or other memory-intensive features, such as spoofing or protocol translations.
the cisco 3631 and cisco 3660 routers contain two 168-pin dimm sockets for sdram. each socket can be filled with a single 64-bit-wide, 168-pin sdram dimm. you can configure sdram as a mixture main memory, which is reserved for the cpu, and shared memory, which is used for data transmitted or received by modules and wan interface cards. see figure 5-10 and figure 5-11 for dimm locations.
to see how much memory is currently installed in the router, enter the show version command while the router is in the privileged exec mode (router# prompt). near the middle of the resulting output, a message similar to the following displays:
cisco 3660(r527x) processor (revision 0x00) with 24576k/8192k bytes of memory.
this line shows how much memory is installed (in this example, 24576k/8192k). the first number represents primary memory and the second number represents shared memory. your router supports up to 256 mb of sdram.
each dimm socket corresponds to one bank of memory. fill banks from 0, and empty banks starting with 1. bank 0 must always be filled first and emptied last.
the cisco 3631 router supports both parity and non-parity pc-100 dimms ranging in capacity from 64 mb to 128 mb. only certain combinations of sdram dimms are permitted. (see table 5-5.)
the cisco 3660 router supports both parity and non-parity pc-100 dimms ranging in capacity from 16 mb to 128 mb. only certain combinations of sdram dimms are permitted. (see table 5-5.)
an advantage of parity dimms over non-parity dimms is easier identification of memory errors; a disadvantage is lower processing speed.
to use a 64-bit mode sdram configuration, the dimm in bank 1 must be less than or equal to the size of the dimm in bank 0.
sdram dimm orientation
dimms have polarization notches to ensure proper orientation and alignment holes to ensure proper positioning. figure 5-12 shows the polarization notches and alignment holes on a dimm.
to avoid damaging esd-sensitive components, observe all esd precautions. to avoid damaging the underlying mainboard, do not use excessive force when you remove or replace dimms.
removing sdram dimms
perform this procedure to remove sdram dimms:
step 1 attach an esd-preventive wrist strap and ensure that it makes good contact with your skin. connect the equipment end of the wrist strap to the metal back plate of the chassis, avoiding contact with the connectors.
step 2 on the mainboard, locate the sdram dimm sockets shown in figure 5-11.
handle dimms by the edges only. dimms are esd-sensitive components and can be damaged by mishandling.
step 3 remove the dimm by pushing the locking spring clips on both sides outward. this ejects the dimm from its socket. (see figure 5-13.)
step 4 hold the dimm by the edges with your thumb and index finger and lift it out of the socket. place the removed dimm in an antistatic bag to protect it from esd damage.
step 5 if necessary, repeat step 3 and step 4 for the other dimm.
installing sdram dimms
perform this procedure to install sdram dimms:
step 1 attach an esd-preventive wrist strap and ensure that it makes good contact with your skin. connect the equipment end of the wrist strap to the metal back plate of the chassis, avoiding contact with the connectors.
step 2 on the mainboard, locate the sdram dimm sockets shown in figure 5-11.
handle dimms by the non-connector edges only. dimms are esd-sensitive components and can be damaged by mishandling.
step 3 hold the dimm with the polarization notch on the right, near the rear of the chassis, and with the connector edge at the bottom.
step 4 beginning with socket 0, insert the dimm perpendicular to the socket. push firmly into place (see figure 5-13), using the minimum amount of force required. when the dimm is properly seated, the socket guide posts fit through the alignment holes, and the locking spring clips click into place.
step 5 ensure that each dimm is straight (perpendicular to the socket). (see figure 5-13.)
it is normal to feel some resistance when installing a dimm, but do not use excessive force on the dimm, and do not touch the surface components.
step 6 repeat step 3 through step 5 for each dimm.
when you finish replacing dimms, and have installed all internal components, proceed to the "replacing the cisco 3660 mainboard tray" section on page 5-33.