TP-LINK TL-R402M v4.0

Overview
Pictures

The above link is dead, but I found some more technical analysis at a review from 2006.

From here, the following information can be confirmed:
 * CPU: Marvell 88E6218 @150MHz
 * Flash: Spansion 4 Mbit (512K x 8-Bit / 256 K x 16-Bit)
 * CMOS 3.0 V with boot sector, using 48-pin TSOP


 * RAM: ISSI IC42S16100 (SDRAM) 512K x 16 Bit x 2 Banks (16-MBit) TSOP II

Also note that the size of a firmware upgrade is usually just below 512KiB.

However, according to that page, the very similar TL-R460 does have
 * 1MB 29LV800B flash and 8MB RAM Samsung K4S641632H-TC75.

See also TP-LINK TL-R450 v4.0..