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5-14
Cisco 3600 Series Hardware Installation Guide
OL-2056-02
Chapter 5 Installing Memory in the Router
Replacing DRAM and SDRAM
SDRAM DIMMs Used in the Cisco 3631 and Cisco 3660 Router
This section describes how to upgrade synchronous dynamic random access memory (SDRAM) dual
in-line memory modules (DIMMs) in the Cisco 3631 and Cisco 3660 routers. You might need to upgrade
the SDRAM DIMMs for the following reasons:
• 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.)
Note An advantage of parity DIMMs over non-parity DIMMs is easier identification of memory errors; a
disadvantage is lower processing speed.
Note 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.