Why does some kind of data, like pictures, take a longer time to get copied

Data is normally stored either in the temporary storage or permanent storage of the computer. Temporary storage is the Random Access Memory (RAM), which needs constant power to keep the data live. Permanent storage mediums are Hard Disk, Floppy Disk, CDRom, USB Flash Memory, etc.

While copying the data, the time taken to transfer the data from one location to another depends on the speed of the medium and the quantity of data that is to be transferred. Pictures and other similar data that are of graphical nature, normally take a lot of space for storage, unlike a text document or spreadsheet.

Because the size of these elements is big, it takes much more time to copy from one location to the other. The above latency (slowness) can also be seen when you browse the internet.

The text contents in a website get downloaded to your browser faster than the pictures. To avoid delay, the quality of the pictures are reduced (which reduces the size too) without affecting the visual quality, and stored in the website. Since these pictures take less amount of space, they get transferred faster from the website to you computer’s browser when browsing the internet. If a text document file containing a number of pages is of the same size as that of a picture, the time taken to copy will be same for both.