. you upgraded the cisco ios feature set or release and it requires additional dram.
. the router maintains large routing tables or other memory-intensive features, such as spoofing or protocol translations.
the cisco 3620 and cisco 3640 routers each contain four 72-pin simm sockets (or banks) for dram. each socket can be filled with a single 32-bit-wide, 72-pin dram simm. you can configure dram as a mixture of primary or 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.
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 3640(r4700) 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.
you can configure dram to be either 32 or 64 bits wide. to use 64-bit mode, you must install dram simms in pairs of the same size. generally, basic software feature sets (such as ip) use 32-bit dram simms and robust software feature sets (such as enterprise) use 64-bit dram simms.
in the cisco 3620 router, dram supports 32-bit operation only, whereas in the cisco 3640 router, dram supports either 32- or 64-bit operation.
in 32-bit mode, the router performs approximately 20 percent slower than when dram is configured for 64-bit mode operation.
each simm socket corresponds to one bank of memory. fill banks consecutively with no gaps; start filling banks from 0, and empty banks starting with 3. bank 0 must always be filled first and emptied last.
only certain combinations of dram simms are permitted. these combinations are shown intable 5-1 for 32-bit configurations used in cisco 3620 routers, table 5-2 for 32-bit configurations used in cisco 3640 routers, and table 5-3 for 64-bit configurations used in cisco 3640 routers.
follow these rules to use 64-bit mode dram configuration:
. simms in banks 0 and 1 must be the same size (in mb) and have the same access time (in nanoseconds).
. simms in banks 2 and 3 must also be the same size and have the same access time.
. simms in banks 2 and 3 must be less than or equal to the size of the simms in banks 0 and 1.
figure 5-5 or figure 5-6 shows the dram simm locations in your router.
1. 8 mb = single-bank simm, 8 mb in size.
2. 8 mb-dual = dual-bank simm, 8 mb in size.
3. 32 mb-dual = dual-bank simm, 32 mb in size.
dram simm orientation
simms have a polarization notch to ensure proper orientation and alignment holes to ensure proper positioning.figure 5-7 shows the polarization notch and alignment holes on a simm.dram simms are installed with the connector edge down and the polarization notch near the front of the chassis.
to avoid damaging esd-sensitive components,observe all esd precautions.to avoid damaging the underilying mainboard ,do not use excessive force when you remove or replace simms.
removing dram simms
perform this procedure to remove dram simms:
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 dram simm sockets shown in figure 5-5 or figure 5-6.
handle simms by the non-connector edges only. simms are esd-sensitive components and can be damaged by mishandling.
step 3 remove one simm at a time, beginning with the simm in bank 3. to lift the simm out of its socket, pull the locking spring clips on both sides outward and tilt the simm toward the right side of the chassis, until it is free of the clips. (see figure 5-8.)
step 4 hold the simm by the edges with your thumb and index finger and lift it out of the socket. place the removed simm in an antistatic bag to protect it from esd damage.
step 5 repeat step 3 and step 4 for each simm.
installing dram simms
perform this procedure to install dram simms:
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 dram simm sockets shown in figure 5-5 or figure 5-6.
handle simms by the edges only. simms are esd-sensitive components and can be damaged by mishandling.
step 3 hold the simm with the polarization notch on the right, near the front of the chassis, and with the connector edge at the bottom.
step 4 beginning with bank 0, insert the simm into the socket at an angle, tilted toward the right side of the chassis. rock the simm into a vertical position (see figure 5-9), using the minimum amount of force required. when the simm 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 simm is straight (perpendicular to the socket), and that the alignment holes (as shown in figure 5-9) line up with the plastic socket guides on the socket.
it is normal to feel some resistance when installing a simm, but do not use excessive force on the simm, and do not touch the surface components.
step 6 repeat step 3 through step 5 for each simm.
when you finish replacing simms, proceed to the "replacing the cover on a cisco 3620 or cisco 3640 router" section on page 5-30.