I mean if we increase the size of a sdram with same technology does the response time get slower? If it does, is it about complexity of digital logic?
Yes and no. As duDE states, memory will never run faster than the bus/clock speed driving it, but the maximum speed of memory definitely is dependent on size.
As a memory assembly gets larger, the number of levels of address decoder increase (with the log of size) and the load on the drivers increases linearly (producing roughly a logarithmic increase in delay).
So, while it is rarely worthwhile to limit the size of RAM in a off-the-shelf system in an attempt to increase speed (there are exceptions where the box adjusts clock speed based on the size of RAM), if you're a system designer the maximum RAM size is one of the performance tradeoffs you must consider.
No. It does not. As SDRAM is synchronized with the system, their speed depends on the speed of the system. What may affect the speed of the memory access is the configuration they are used in.
If your build already has a
dual-channel(or triple channel) configuration, and the increased memory does not use identical modules, then you may slow down to single channel operation. However, this decrease is hardly noticeable, as Wikipedia says :
Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a "modern (2007)" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks.
In this case the "speed" may decrease, but you will experience an overall boost in performance due to the greater amount of physical memory available at the disposal of your OS. This, of course, depends on the OS you are using and how efficient it is at utilizing the available resources.