Size on Disk

OK.

1. In file properties, what is the difference between "file size" and "size on disk "?

2. Which size do I trust when view the size of a web page and an image directory. Which file size is the actual download size?

Thanks

Mathew

 

This is part of the inherent confusion when we try to interface with computer type people. A megabyte is typically 1048576 bytes to them and a kilobyte is 1024 bytes. We common mortals like to think of things in the decimal tradition whereas a meg is 1,000,000 and a kilo is 1,000. It usually doesn't matter and sometimes the people selling their products choose the decimal system to make their product seem larger than it would otherwise.

You can use the conversion ratio of .9536743 to multiply the decimal value and get the binary equivalent. Conversely you can use the reciprocal of that, 1.048576 to multiply the binary value and get the decimal equivalent.

As to telling you who is using what term at any given time, I wouldn't want to guess. I don't trust any of them.

Then there's the byte versus bit confusion and who's using what term there. That's a whole 'nother mess.

 

Files are stored in units of space called clusters. Depending on the file system (NTFS or FAT32) and the size of the partition, the cluster size varies.

If using NTFS, for example, the default cluster size is 4KB so a small file (up to 4KB) uses one cluster or 4KB - even a one byte file takes 4KB. A file larger than 4KB say 6KB, takes two clusters, or 8KB, and so on.

So "Size on Disk" is always larger than the actual size of the files, unless all your files are exact multiples of your cluster size.