In a typical read operation from a dram chip, all the banks are equipped with sense amplifiers which select one bit from each bank using column multiplexer. But how does write operation takes place? How does only one column in a bank is written in a particular row?
When reading the row then bits are amplified and sent back on the line as part of the feedback circuit. The bits are also stored in a small chunk of SRAM where they are cached for reads and writes.
writes to the rows don't happen immediately, only when unloading the data from the cache.
When unloading the cache the feedback circuit normally used to refresh the data is overridden with the new values in the row. All bits of the row are written.