Terms of Use
Last updated: 31 July 2026
1. Who these terms are with
DiskDyno is published by Johnston Software & Services, LLC, an Oregon limited liability company ("we", "us"). These terms are an agreement between you and us.
Johnston Software & Services, LLC
PO Box 230614
Tigard, OR 97281
United States
This agreement is not with Apple. Apple is not a party to it. Apple is not responsible for DiskDyno or its contents, and Apple has no obligation to provide you any support for it. See ยง14.
2. Accepting these terms
By downloading or using DiskDyno you accept these terms. If you do not accept them, do not use the app. You must be old enough to form a binding contract where you live.
3. Your licence
We grant you a personal, non-transferable, non-exclusive licence to use DiskDyno on any Apple-branded device that you own or control, as permitted by the App Store Usage Rules in Apple's Media Services Terms and Conditions.
You may not sell, rent, sublicence, or redistribute the app, and you may not reverse engineer, decompile, or disassemble it except where that restriction is prohibited by law. We keep all rights we do not expressly grant you here.
4. What DiskDyno is
DiskDyno measures how fast a storage device reads and writes, and rates how much confidence its own measurement deserves. It works by writing a temporary file of its own, reading it back, timing both, and then deleting it.
It can test your device's internal storage, which needs nothing from you, or any other drive, which you give it access to by selecting a folder through the iOS file picker. The drive-to-drive transfer test works on two drives at once and asks you to select a folder on each.
5. What DiskDyno is not, and what it cannot tell you
This section matters more than most of this document. Please read it.
A measurement is not a guarantee. DiskDyno reports what it measured on your device, with your drive, your cable, and your port, at the moment you ran it. Storage performance varies with temperature, how full the drive is, its firmware, its age, what else the system is doing, and the physical connection. A result is evidence, not a specification, and not a promise about what that drive will do next time.
Format guidance is an estimate. Where DiskDyno tells you which video formats a drive appears able to sustain, it is comparing your measured sustained speed to published data rates. It does not account for your camera, your recording settings, your file system's behaviour when nearly full, or a drive that slows as it heats up. Do not treat it as a guarantee that a recording will complete. Test your own workflow before you rely on it.
DiskDyno does not detect counterfeit or misdescribed drives. It measures speed, not capacity. A drive that reports a false size will not be caught by DiskDyno. Do not use this app to decide whether a drive is genuine.
DiskDyno does not repair, recover, or diagnose failing hardware. A poor result may have many causes. It is not a diagnosis.
6. Your data and your drives
Back up before you test. DiskDyno writes large temporary files to the location you choose and removes them when it is finished with them. This is ordinary file activity, but it is activity on a drive that may hold work you care about, and while a run is in progress it occupies an amount of free space up to the test size you selected. A drive-to-drive transfer test occupies that space on both drives at the same time. Asking DiskDyno to explain a transfer result runs further tests on both drives, which write and remove their own files again.
You are responsible for having a backup of anything on a drive you test. Do not run a benchmark on the only copy of anything.
Cleanup is best effort. DiskDyno removes its temporary files when a run finishes, is cancelled, or fails. It does not retry a removal that the drive refuses, and it does not sweep for files left behind by an earlier run. It also writes a small hidden file named .diskdyno-write-probe when you select a folder, to check the drive is writable, and removes it immediately. If a drive is disconnected, is full, or turns read-only at the wrong moment, one of these files can be left on it. They are inert and safe to delete, and you may delete any file beginning with .diskdyno- or diskdyno- at any time.
Do not disconnect a drive mid-run. Removing a drive, or removing power from a hub, while a test is writing can leave a temporary file behind or, on some hardware, damage the file system on that drive. Cancel the run and wait for it to stop before you unplug.
Your results belong to you. Saved results are files on your device. We never receive them. We cannot recover them for you if you delete the app or lose the device. See the Privacy Policy.
7. DiskDyno Pro
DiskDyno is free to use. Additional capabilities are available through DiskDyno Pro, a one-time purchase. It is not a subscription. It does not renew, and there is nothing to cancel.
The price shown in the app is the price Apple gives us for your storefront, in your currency, including any tax Apple collects. Prices can change for future purchasers. A purchase you have already made is not affected by a later price change.
Restoring. A purchase is tied to your Apple Account, not to a device. You can restore it on your other devices, and after reinstalling, using the restore option in the app. You do not pay again.
Refunds are handled by Apple. We do not process payments and we cannot issue refunds. Requests go through Apple at reportaproblem.apple.com, under Apple's refund policy. If you have a problem with the app, contact us anyway. We would rather fix it.
What you are buying. You are buying access to the capabilities described in the app at the time of purchase. We may add to DiskDyno Pro. We will not move a capability out of DiskDyno Pro and put it behind a second, separate purchase.
8. Things you agree not to do
Do not use DiskDyno to break the law. Do not use it on a device or drive you are not authorised to use. Do not try to defeat the purchase mechanism or obtain paid capabilities without paying for them.
9. Changes to the app
We may change, add, or remove features in future versions. We may stop publishing DiskDyno. If we do, the copy already installed on your device keeps working for as long as your device and its operating system support it, and you keep your saved results, because they are already on your device.
Because DiskDyno operates no service, there is nothing we can switch off remotely that would stop your installed copy from working.
10. No warranty
DiskDyno is provided "as is" and "as available", without warranty of any kind. To the fullest extent permitted by law, we disclaim all warranties, express or implied, including any implied warranty of merchantability, fitness for a particular purpose, accuracy, and non-infringement.
We do not warrant that the app will be uninterrupted or error free, or that its measurements will be accurate, complete, or suitable for any particular decision you are making.
Some jurisdictions do not allow the exclusion of implied warranties, so some of the above may not apply to you. You may have other rights that vary by jurisdiction, and nothing in these terms limits any right you have that cannot be limited by law.
11. Limitation of liability
To the fullest extent permitted by law, we are not liable for any indirect, incidental, special, consequential, exemplary, or punitive damages, or for any loss of data, loss of profits, loss of revenue, loss of a recording, or cost of substitute goods, arising out of or relating to your use of DiskDyno, under any theory of liability, even if we have been advised that such damages are possible.
To the fullest extent permitted by law, our total liability for all claims relating to DiskDyno is limited to the greater of the amount you actually paid us for the app in the twelve months before the claim, or five United States dollars.
Some jurisdictions do not allow these limitations, so some of the above may not apply to you.
12. Indemnity
You agree to indemnify us against claims arising from your use of DiskDyno in breach of these terms or in breach of the law.
13. Governing law
These terms are governed by the laws of the State of Oregon, United States, without regard to its conflict-of-laws rules.
If you are a consumer, this does not deprive you of the protection of any mandatory law of the country where you live, or of the right to bring proceedings where that law entitles you to.
If any part of these terms is held unenforceable, the rest stays in force.
14. Apple
These terms are between you and us only, not with Apple. Apple is not responsible for DiskDyno or its contents.
Apple has no obligation to provide any maintenance or support for DiskDyno. If the app fails to conform to any warranty that applies, you may tell Apple, and Apple will refund the purchase price if any. To the maximum extent permitted by law, Apple has no other warranty obligation with respect to DiskDyno.
We, not Apple, are responsible for addressing any claim by you or a third party relating to DiskDyno, including product liability claims, any claim that it fails to conform to a legal or regulatory requirement, and any claim arising under consumer protection or similar law. We, not Apple, are responsible for investigating and defending any claim that DiskDyno infringes a third party's intellectual property rights.
You represent that you are not located in a country subject to a United States Government embargo or designated as a terrorist-supporting country, and that you are not on any United States Government list of prohibited or restricted parties.
Apple and Apple's subsidiaries are third-party beneficiaries of these terms, and Apple has the right to enforce them against you.
15. The whole agreement
These terms, together with the Privacy Policy, are the entire agreement between you and us about DiskDyno, and replace anything said earlier on the subject. If we do not enforce a provision, that is not a waiver of it.
16. Contact
Johnston Software & Services, LLC
PO Box 230614
Tigard, OR 97281
United States