The definition information for symptom substitution is provided by Stedman's. You can search our medical dictionary here. Stedman's, part of Lippincott Williams & Wilkins, provides a comprehensive line of health-science publications for healthcare professionals and medical students.
Gigabyte: A Gigabyte is approximately 1,000 Megabytes. A Gigabyte is still a very common term used these days when referring to disk space or drive storage. 1 Gigabyte of data is almost twice the amount of data that a CD-ROM can hold. But it's about one thousand times the capacity of a 3-1/2 floppy disk. 1 Gigabyte could hold the contents of about 10 yards of books on a shelf. 100 Gigabytes could hold the entire library floor of academic journals.
TB: TeraBytes, GB: Gigabytes. There are 1000 gigabytes in a terabyte. 1 TeraByte is equal to 1000 Gigabytes. 1 TB = 1000 GB. Just a few years ago a use of terabyte, a unit for data volume in digital technology, was something exceptional for the specialists. But nowadays operating with such amounts of information as 1 terabyte, or 1012bytes (1 000 bytes), is becoming more and more common.