SD vs xD
xD and SD cards are two storage media that are used in a wide variety of devices, including digital cameras. The most notable difference between these two is in the capacity. xD cards have a theoretical maximum capacity of 8GB but you cannot find one that is over 2GB. SD cards have a maximum capacity of 4GB while newer versions have extended the maximum capacity to 32GB and even 2TB.
SD cards also have the speed advantage over xD cards. This is something that is quite desirable in digital cameras because this means you can shoot higher quality photos. Initially, xD cards were smaller and more compact compared to SD cards. But the advent of the mini and micro versions are much smaller compared to xD and are quite ideal for mobile phones that are always short of space. Surprisingly, xD cards costs a lot more compared to SDs. This is probably due to in part of the proprietary nature of xD cards and the fees that are usually associated with it.
Another contributing factor to the superiority of SD cards is a feature called wear levelling. Flash memory can only be written to up to a certain amount of times before certain elements fail. Wear levelling is a system that determines how much each area has been written to and places new files to the areas with the least amount of wear. This helps ensure that all the elements are fairly used before any failure starts happening. xD cards do not have this feature and as a result, the first memory elements are already failing while the rear elements have not even seen a substantial amount of use. Simply put, SD cards tend to last a lot longer than xD cards with the same level of usage.
Because of the great number of disadvantages with using xD cards, it is being consistently replaced by SD in portable devices. Consumers are shying away from devices that use xD cards because of its high price and poor performance. Consequently, manufacturers have also begun to move along with the consumers who buy their products.
Summary:
1.SD cards have much greater capacities than xD cards
2.SD cards are faster than xD cards
3.xD cards are also generally smaller than SD cards but not the mini and micro versions
4.xD cards costs more than SD cards
5.xD cards have no wear levelling like SD cards do