Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteDisk access time is the delay before a disk can provide requested data. For a rotating hard disk (HDD), the term may mean only the time to position the read/write head and wait for the requested sector, or it may include the time to transfer the data. Because sources use both definitions, check what a quoted figure includes.
How an HDD reaches data
A read or write request on a rotating hard disk typically involves three stages:
As an Amazon Associate I earn from qualifying purchases.
- Seek time: The time for the read/write head to move to the track containing the requested data. NPTEL and OpenDSA describe this movement as the seek stage.
- Rotational latency: Once the head is positioned, the disk platter rotates until the desired sector is beneath it. The University of London explains average rotational latency as half a revolution when requests arrive at random times and are uniformly distributed around the rotation.
- Transfer time: The time taken to read or write the requested data after it is positioned. It depends on the amount of data and the transfer conditions.
NPTEL describes a sector as the smallest unit of information that can be read from or written to disk. The three stages are sequential, but whether all three count as “disk access time” depends on the definition being used.
Recommended Free Tools
Which formula does disk access time use?
Two conventions appear in educational materials. The University of London and Simon Fraser University (SFU) use access time for positioning the disk through the point when data transfer begins. NPTEL and Emory course slides use a broader calculation that also counts the transfer itself.
#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.
| Convention | Formula | What the result covers |
|---|---|---|
| Positioning latency | Seek time + rotational latency | Time to position the head and wait for the requested sector; ends when transfer begins. SFU distinguishes this access time from transfer rate in its performance-measures notes. |
| Broader total time | Seek time + rotational latency + transfer time | Positioning plus the time to read or write the requested data, as in the broader convention shown in Emory course slides. |
Some system-level I/O measurements also count queueing and controller or operating-system delays. A response-time measurement that includes those components should not automatically be treated as the drive’s access time; state what the measurement includes.
Why rotational latency is often half a revolution
If a request arrives at a random point in a uniformly rotating disk’s cycle, the wait for the target sector can range from nearly zero to nearly one full revolution. The average under that model is half a revolution. To calculate it from a known rotation rate, use half the time for one rotation; the result depends on the spindle speed and those assumptions. It is not a guarantee of the latency for any particular request.
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.
What an access-time figure can—and cannot—tell you
A number is useful only when its measurement is defined. Before comparing figures, identify:
PC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Outdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware match- Device type: Seek and rotational latency describe mechanical HDD behavior. Do not apply those platter-based stages to solid-state storage (SSD); the cited teaching materials do not establish a detailed current SSD latency model.
- Metric definition: Check whether the figure ends at the start of transfer or includes transfer time, and whether it includes system-level delays.
- Request pattern and size: Random and sequential requests behave differently, and transfer time depends on how much data is requested.
The cited educational materials include historical or illustrative figures, not a current universal benchmark for disk access time. A value without its device, workload, data amount, and timing definition cannot support a sound comparison. For context, see SFU’s performance-measure notes and Stanford CS111’s Spring 2021 lecture on disks.
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.
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.
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.
