What Is a Sector? Disk Sector Definition
What Is a Sector? (Disk Sector Definition) GA S REGULAR Menu Lifewire Tech for Humans Newsletter! Search Close GO Computers, Laptops & Tablets > Accessories & Hardware 37 37 people found this article helpful
It's not very common to change the default allocation unit size of a drive. Microsoft has these tables that show the default cluster sizes for the NTFS, FAT, and exFAT file systems in different versions of Windows. For example, the default AUS is 4 KB (4096 bytes) for most hard drives formatted with NTFS. If you do want to change the data cluster size for a disk, it can be done in Windows when formatting a hard drive but disk management programs from 3rd party developers can do it, too. While it's probably easiest to use the formatting tool that's built-in to Windows, our Free Disk Partitioning Tools list includes several free programs that can do the same thing. Most offer more unit size options than Windows does.
What Is a Sector?
Explanation of disk sector sizes and repairing damaged sectors
By Tim Fisher Tim Fisher Senior Vice President & Group General Manager, Tech & Sustainability Emporia State University Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the VP and General Manager of Lifewire. lifewire's editorial guidelines Updated on September 11, 2021 Tweet Share Email Tweet Share EmailIn This Article
Expand Jump to a Section What Do Different Sector Sizes Mean Allocation Unit Size Changing the AUS of a Disk Repair Bad Sectors More Information on Disk Sectors Frequently Asked Questions A sector is a specifically sized division of a hard disk drive, optical disc, floppy disk, flash drive, or another kind of storage medium. A sector may also be referred to as a disk sector or, less commonly, a block.What Do Different Sector Sizes Mean
Every sector takes up a physical location on the storage device and is usually made up of three parts: the sector header, the error-correcting code (ECC), and the area that actually stores the data. Usually, one sector of a hard disk drive or floppy disk can hold 512 bytes of information. This standard was established in 1956. In the 1970s, larger sizes such as 1024 and 2048 bytes were introduced to accommodate larger storage capacities. One sector of an optical disc can usually hold 2048 bytes. In 2007, manufacturers began using Advanced Format hard drives that store up to 4096 bytes per sector in an effort to both increase the sector size as well as improve error-correcting. This standard has been used since 2011 as the new sector size for modern hard drives. This difference in sector size doesn't necessarily imply anything about the difference in possible sizes between hard drives and optical discs. Usually, it's the number of sectors available on the drive or disc that determines capacity. Stanley K Patz / Photolibrary / Getty ImagesDisk Sectors and Allocation Unit Size
When formatting a hard drive, whether using Windows' basic tools or via a free disk partitioning tool, you're able to define a custom allocation unit size (AUS). This is essentially telling the file system what the smallest portion of the disk that can be used to store data is. For example, in Windows, you can choose to format a hard drive in any of the following sizes: 512, 1024, 2048, 4096, or 8192 bytes, or 16, 32, or 64 kilobytes. Let's say you have a 1 MB (1,000,000 byte) document file. You can store this document on something like a floppy disk that stores 512 bytes of information in each sector, or on a hard drive that has 4096 bytes per sector. It really doesn't matter how large each sector is, but only how large the entire device is. The only difference between the device whose allocation size is 512 bytes, and the one that's 4096 bytes (or 1024, 2048, etc.), is that the 1 MB file must be spanned across more disk sectors than it would on the 4096 device. This is because 512 is smaller than 4096, meaning less "pieces" of the file can exist in each sector. In this example, if the 1 MB document is edited and now becomes a 5 MB file, that's an increase in size of 4 MB. If the file is stored on the drive using the 512-byte allocation unit size, pieces of that 4 MB file will be spread across the hard drive into other sectors, possibly in sectors further away from the original group of sectors that hold the first 1 MB, causing something called fragmentation. However, using the same example as before but with the 4096-byte allocation unit size, fewer areas of the disk will hold the 4 MB of data (because each block size is larger), thus creating a cluster of sectors that are closer together, minimizing the likelihood that fragmentation will occur. In other words, a larger AUS generally means files are more likely to stay closer together on the hard drive, which in turn will result in quicker disk access and better overall computer performance.Changing the Allocation Unit Size of a Disk
Windows XP and newer Windows operating systems can run the fsutil command to see the cluster size of an existing hard drive. For example, entering this into a command-line tool like Command Prompt will find the cluster size of the C: drive: fsutil fsinfo ntfsinfo c:It's not very common to change the default allocation unit size of a drive. Microsoft has these tables that show the default cluster sizes for the NTFS, FAT, and exFAT file systems in different versions of Windows. For example, the default AUS is 4 KB (4096 bytes) for most hard drives formatted with NTFS. If you do want to change the data cluster size for a disk, it can be done in Windows when formatting a hard drive but disk management programs from 3rd party developers can do it, too. While it's probably easiest to use the formatting tool that's built-in to Windows, our Free Disk Partitioning Tools list includes several free programs that can do the same thing. Most offer more unit size options than Windows does.