The larger the capacity (in gigabytes, or GB) of your hard drive, the more space is available to store your files and applications. A typical application today may take 10 to 50 megabytes (MB); photos may take up about 2-4MB each; graphics files can occupy more than 100MB; and video files are often many gigabytes in size.
MacBook Pro also offers an optional 128GB, 256GB, or 512GB solid-state drive, which has no moving parts for enhanced durability. These are new third-generation SATA solid-state drives, which are up to 4x faster than a traditional hard drive.
All drives come formatted in the Mac OS Extended file format for efficient storage of your data.
Important note: For hard drive capacity measurements, 1GB = 1 billion bytes; actual formatted capacity less.