The sensor in a digital camera is equivalent to the film in a film camera. Basically, the larger the sensor the better the image. Large sensors provide more light per pixel (picture element) permitting lower “noise” (grainy effect) and higher quality of contrast and colour. Sensor sizes can be grouped into small and large.
Small sensors range between 4x3mm and 7x5mm. High-end compact cameras generally use a sensor size of 7x5mm, which is three times the size of a 4x3mm. Ultra compact cameras with a reasonable zoom use the smaller size sensors, putting convenience before image quality.
Large sensors range between 18x14mm (four thirds) and 36x24mm (full frame) and are mostly used in single-lens reflex (SLR) cameras. These sensors provide images of high quality, with the disadvantage of making cameras more bulky.
Memory cards are used to store information from cameras and other devices. They use flash memory, a non-volatile computer storage chip with memory that can be erased and reused and which requires no power to store data recorded to it.
As with most advanced technology, the cards have reduced in price whilst improving in performance and capacity. Memory cards come in various sizes regarding capacity and transfer speeds. Capacity is usually given in gigabytes (GB), whilst speed is sometimes given in megabytes per second (MBPS) or with an x suffix such as 100x, where 1x equals 150kbps. A 100x speed is thus equivalent to 15MBPS.
The class system of SD (Secure Digital) cards is simpler. A class 2 card has a minimum transfer rate of 2MBPS, a class 4 card 4MBPS and so on.