The capacity is shown in "Megabyte" (same with Hard Disk Drive, 1MB = 1000KB). In Windows environment or DOS mode, 1MB equals to 1024 KB. Therefore 1GB is approximate 953MB.
The actual available memory on the device is less than what is listed on the package. This is due to small discrepancies in file format and algorithms used by various operating systems. In addition, a portion of memory space is reserved for system files and data sectors for better performance.