After fixing motherboard along with processor and SMPS to ATX cabinet, next step is to fix or install RAM (Random Access Memory), hard disk drive and CDROM-RW/DVD-RW/COMBO DRIVE to the cabinet.
RAM (DDR1 or DDR2 or DDR3) depends on the motherboard you have purchased. Some motherboard supports DDR1 RAM and some support DDR2 or DDR3. Make sure that you check with your hardware vendor for the supported RAM to the purchased motherboard. DDR1 and DDR2 can be distinguished as shown in the below image.
Take the RAM and place it on the motherboard in the RAM slot
as shown in the image
Make sure that when placing RAM in RAM slot the distance between either side of the notch on the motherboard has to match that of RAM.
After placing RAM in the slot, press firmly towards motherboard to get locked by the RAM lock
Below image shows the difference between the RAM which is locked and unlocked.
After RAM is fixed, take the hard disk drive and CDROM-RW/DVD-RW/COMBO DRIVE and fix them to cabinet as shown in the image.