Quick wins for a faster PC:
Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →A file allocation unit—also called a cluster—is the smallest amount of disk space a filesystem can allocate to hold file data. Because files are accounted for in whole allocation units, “Size on disk” can be larger than a file’s “Size.” The unit’s size depends on the filesystem and volume configuration.
What is a file allocation unit?
A file allocation unit is the filesystem’s basic unit for assigning storage to file data. Microsoft describes cluster size, another name for allocation unit size, as the smallest amount of disk space that can be allocated to hold a file. Microsoft’s explanation of cluster size uses the terms “cluster” and “allocation unit” for this concept.
As an Amazon Associate I earn from qualifying purchases.
Allocation units are not the same thing as a drive’s physical sector size. The allocation unit is a filesystem-level measurement; physical sectors are a characteristic of the storage device. “Block” can also refer to a related unit, but terminology and implementation vary across filesystems.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Why “Size” and “Size on disk” can differ
A file’s logical size is the amount of data it contains. The space reported as used on disk reflects how the filesystem allocates storage for that data. Since allocation happens in units rather than arbitrary byte increments, the last unit assigned to a file may have unused space. That slack space can make the on-disk figure larger than the file’s logical size.
#1 Best Overall
- Easily store and access 2TB to content on the go with the Seagate Portable Drive, a USB external hard drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
For example, if a file needs some space within an allocation unit but does not fill that unit, the unused remainder is still part of the allocated space. Microsoft’s NTFS support guidance explains that NTFS allocation grows in multiples of the cluster size. This is why a folder’s total “Size on disk” may not match its total “Size.”
That accounting difference alone does not mean files are duplicated or that a scan has found extra files. A count discrepancy, however, cannot be explained by allocation-unit size: the distinction affects space accounting, not how many directory entries exist.
Rank #2
- Easily store and access 5TB of content on the go with the Seagate portable drive, a USB external hard Drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Small files and NTFS
Do not assume that every tiny NTFS file necessarily occupies a full data cluster. Microsoft’s filesystem comparison describes NTFS tail packing: small files can be stored resident in the Master File Table (MFT) stream descriptor. Compression can also alter the relationship between a file’s logical size and its allocated space.
Free tools Windows power users keep installed
One-click scans. No signup required.
Allocation-unit size depends on the filesystem
There is no universal allocation-unit size. Microsoft’s NTFS overview gives 4 KB as the default cluster size in its documented Windows NTFS context. By contrast, Microsoft’s exFAT specification permits cluster sizes up to 32 MB under the specification’s stated sector-size limits. These are examples for different filesystems, not competing defaults for the same volume.
Rank #3
- Easily store and access 1TB to content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop. Reformatting may be required for Mac
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Cluster size can affect both space efficiency and performance. The right choice depends on the filesystem, workload, and deployment; Microsoft’s guidance discusses different performance benefits for different sizes rather than identifying one best size for every use.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to consider when choosing a cluster size
- Small-file space use: Larger allocation units can leave more unused space in a partially filled unit, although NTFS tail packing is an important exception for some small files.
- Workload and performance: The effect of cluster size depends on how the volume is used. Consider the actual workload rather than assuming that a larger or smaller unit is always faster.
- Filesystem features and compatibility: NTFS, exFAT, and other filesystems differ in their features and supported environments. Choose a filesystem that meets the volume’s compatibility and feature requirements.
- Volume and file limits: Supported limits can depend on filesystem, cluster size, and operating-system context. Microsoft’s NTFS overview and filesystem comparison document relevant differences.
Allocation-unit settings should therefore be considered as part of a filesystem and volume decision, not as a hardware specification. The figures in Microsoft’s NTFS and exFAT documentation apply to those documented contexts and should not be generalized to every filesystem or operating system.
Quick Recap
Best Value
- [Upgraded Version] - This external hard drive features a mirrored logo stripe combined with a striped anti-slip design, and the rounded corners of the casing make it easier to grip. The stripes also have a heat dissipation function, ensuring stable and fast data transfer.
- 【Ultra-thin and quiet】 - The motherboard adopts JMicron 578 noise-free solution, giving you a quiet working environment. Lightweight and portable size designed to fit in your pocket for easy portability.
- 【Ultra-Fast Data Transfers】 - Pairing this external hard drive with JMicron 578 solution USB 3.0 and USB 2.0 interfaces enables blazing-fast data transfer. It boasts theoretical read speeds of up to 125MB/s and write speeds of up to 103MB/s.
- 【Plug and Play】 - With no software to install, just plug it in and the drive is ready to use.The hard disk chip is wrapped with an aluminum anti-interference layer to increase heat dissipation and protect data.
- 【What You Get】 - 1 x Portable Hard Drive, 1 x USB 3.0 Cable, 1 x User Manual, Gift-type shell packaging ,Three-year manufacturer's warranty and free technical support services.
Rank #4
- Easily store and access 4TB of content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
