Depending on your motherboard it is most likely because most motherboards can only use one type of ram at a time. So you can only use ddr with more ddr to see more than one stick of ram.
Yes you can. There's also an option in the CMOS setup to enable or disable this feature if your motherboard supports it.
It is difficult unless the motherboard supports DDR slots.
No you cannot the ECS P4VXASD2 supports the following:Two 184-pin 2.5V DDR SDRAM (DDR266/DDR200) Maximum: 2GB DDR or SDRAM (Buffered) / 1GB DDR or SDRAM (Unbuffered)
The Intel D845GLLY motherboard supports a maximum of 2GB of PC133 SDRAM, using two 1 GB modules.
Dual-channel architecture requires a dual-channel-capable motherboard and two or more DDR, DDR2 SDRAM, or DDR3 SDRAM memory modules. The memory modules are installed into matching banks, which are usually color-coded on the motherboard.
No.
In order to upgrade SDRAM with DDR, you will need to replace your motherboard. DDR uses a different slot than SDRAM, so if your motherboard is using SDRAM currently, you will most likely have to replace your motherboard in order to make your system support DDR.
No.
The positions of two notches on a SDRAM DIMM identify the type of DIMM and the voltage requirement and also prevent the wrong type from being installed on a motherboard.
DDR or SDRAM
No.
No. SDRAM has two notches and DDR SDRAM has only one so besides all the electrical incompatibilities it won't physically fit.