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Cisco 3600 Series Hardware Installation Guide
OL-2056-02
Chapter 5 Installing Memory in the Router
Replacing DRAM and SDRAM
DRAM SIMMs (Used in Cisco 3620 and Cisco 3640 Routers)
This section describes how to upgrade DRAM single in-line memory modules (SIMMs) in Cisco 3620
and Cisco 3640 routers. You might need to upgrade the DRAM SIMMs for the following reasons:
• 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.
Note 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.
Note 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.