Memory card storage sizes VS actual storage capacity

Why Advertised Storage Does Not Match The Usable Data Capacity

The main reason comes down to differences in the way that operating systems, such as Windows display storage devices, and how USB Flash Drive & other storage device manufacturers advertise the storage capacity.

Computers are based on binary math, which means storage is counted using base 2, not base 10, which storage is advertised as. So, while we measure a kilobyte as 1,000 bytes, Windows refers to a kilobyte as 1,024 bytes.

Let's take an example of a 256GB Flash Drive.

From the manufacturer's point of view, 256GB will have 256*1000*1000*1000 = 256,000,000,000 bytes.

However, computers are calculated in Binary (base 2), so 256GB is actually 256*1024*1024*1024 = 274,877,906,944 bytes.

Hence the discrepancy!

There are also other factors to take in to account as some storage capacity is allocated for overheads, such as the boot data and file system.

What does SDHC Class X Mean? 

Well the simple answer is it relates to the performance of the memory card - where the higher the number equals better performance. Take a look at this table for more information on current SDHC Classes.

Class	Minimum performance	Application
Class 2	2 MB/s	SD video recording
Class 4	4 MB/s	High-definition video (HD) recording including Full HD (from 720p to 1080p/1080i)
Class 6	6 MB/s
Class 10	10 MB/s	Full HD (1080p) video recording and consecutive recording of HD stills (high-speed data bus)
UHS Speed Class 1 (U1)	10 MB/s	Real-time broadcasts and large HD video files (UHS bus)
UHS Speed Class 3 (U3)	30 MB/s	4K video files (UHS bus)

So how many pictures can my camera store on a memory card?

What about my DSLR? In Uncompressed RAW format?