Terminology for larger and larger disk drive data volumes

When I started into the world of computing at university, 200-300 MB hard drives were the norm for PC’s. My own first PC had what was then thought a sizable 1.6 GB disk and things have increased in size since then. I now have access to several hundred gigabytes of storage at home and we are now seeing 1TB offerings for the PC market.

Terabyte storage has been the preserve of the server market but given the disk sizes that are available now, even larger units are needed to describe the sizes of data volumes, ones that I haven’t seen before. So here goes:


Number of bytes
(in next smaller unit)

Number of bytes

Number of bytes


 1024 TB 




 1024 PB 




 1024 EB 




 1024 ZB 



* Binary measurements are used by operating systems like Windows while decimal ones are used by hard drive manufacturers

 I know that the above strays into the realms of esoterica but, with the way that things have been going, we may be talking about petabytes before very long. As it so happens, HP recently mentioned zettabytes when talking about its range of UNIX servers and I needed to go looking up what it meant…