Pasted file has more MB than the copied?

Ok so I have ubuntu 15.10 installed on a USB and boot with it as my main OS on this computer.

The computer has 2 hard disks one connected to a SATA interface and one through USB too... none of them is associated in any way with the main OS I just mounted them to copy my personal folder (from windows users folder) from one disk to an other...

because I was bored I chose to copy the entire folder (with appdata etc) anyway the entire folder was 24 GB according to ubuntu with 81167 files so I copied this folder from lets say drive A to drive B and in drive B 81065 files were copied (some authentication/certificate files in appdata couldnt be copied by ubuntu clicking on "details" shows that ubuntu cant copy "special files" anyway) though less files were copied the folder to the destination drive B is 24.2 GB (instead of being less than 24 or at least equal to that)

how come?

1 Answer

Windows assumes that there are 1024 Bytes in a Kilobyte unit, and 1024 Kilobytes in a Megabyte unit. While Ubuntu assumes, a 1000 bytes constitute a Kilobyte (KB) unit, 1000 Kilobytes for a Megabyte (MB) and so on.

Windows is using the ‘binary prefix’, and Ubuntu or GNU/Linux, is using it in its ‘proper’ foam.

further read here.