What Is a File Size?

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  • Written By: Michael Smathers
  • Edited By: Jessica Seminara
  • Last Modified Date: 05 November 2019
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On a computer, a file's size is the amount of space it takes up on the hard drive. The most basic unit of file size, a byte, is a string of eight binary digits, or bits, in binary code. File size generally depends on the type of file; text documents are generally smaller than graphic-heavy documents or applications. Large files indicate more information stored in binary; the computer can also use decimal, or base 10, like humans use; or hexadecimal, base 16.

Information in a computer, at its most basic level, is represented by electrical impulses traveling along a circuit at a set voltage. Different sequences of these impulses represent different types of information. Computers acknowledge only two states of charge for a circuit: on, represented by a 1; or off, represented by a 0. In binary code, each digit, 0 or 1, is known as a bit, and eight of these bits make up a byte, the most basic unit of file size.


File size can vary depending on what type of file the computer is storing; for example, a text document in Notepad could be kilobytes, or thousands of bytes. An installation program could be millions of bytes, or megabytes. Although a kilobyte is commonly thought to be equal to 1,000 bytes and a megabyte is equal to 1,000 kilobytes, this is actually not the case. As computers use a base 2 system, all measurements must be powers of two; hence, the actual conversion factor is 1,024.

Computer hard drives store these bytes as a series of magnetic imprints on the surface of a disk and the disk head reads them to transmit information to the processor and output devices, similar to how a laser reads an optical disk drive and transmits data. Hard disks contain a set number of sectors, each with a subsection of clusters which in turn contain the magnetically-charged portions of the disk. The file size is the amount of physical space taken on the hard drive; file systems are organizational methods formatted onto the drive to determine how a hard drive stores and accesses its data.

A file size determines how much hard drive space is reserved by a given file. Even after the file is deleted, its information remains on the drive and can be recovered. Deleting a file only removes the 'read-only' aspect of the drive which prevents the drive from writing over the file.

There are two main classes of file systems in use: File Allocation Table (FAT) and New Technology File System (NTFS). FAT stores data in clusters of a set size and wraps the data over to the next cluster. These systems are useful for smaller drives, because the maximum partition size is 4 gigabytes. NTFS is the standard for every operating system since Windows NT. It is used for larger drives.


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Post 3

@croydon - In some ways it worries me a little, to be honest. At least when people were storing their data on discs, or better yet, on paper, it wasn't hanging there somewhere in the ether where it could easily be misplaced.

I still try to reduce my file sizes because I store a lot of stuff in the cloud and it can be expensive. But I make sure that's not the only place I store it.

Post 2

@bythewell - Honestly, I don't think many people are going to be concerned with reducing file size that much these days unless they are creating a file for a particular purpose, like a thumbnail, in which case they won't have multiple types of files in a single packet.

Storage space is just so cheap and ubiquitous it's really incredible. When I think back to how impressed I was when DVDs first came out and you could store a whole movie, or even more than one on a single disc, I'm astonished how quickly we've come to the point where you can store thousands of movies in a little box the size of a palm.

Post 1

If you are worried about large file sizes, particularly for files that shouldn't be very large, I would double check that you haven't accidentally put any images or video files in with your text. Video file size is huge compared with text and even one simple image can also double the size of your file. I often get tripped up with this when deciding on what ebook to read next on my e-reader (given particular time constraints).

I look at the file size when judging which one to read and am misled by the ones that look bigger than they are because they have a fancy cover image that takes up a lot of space.

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