View source for Non-removable-media disk

'''Non-removable-media disk'''s were the generation of [[magnetic storage|magnetic]] [[disk]] [[mass storage]] [[peripheral]]s after the previously ubiquitous [[removable-pack disk‎]]s. They used 'head/disk assemblies' (HDAs), which packaged the [[platter]]s and the [[head]]s in a pre-assembled, sealed (in 'clean-room' conditions), unit. The sealed HDA was, and remains, a key step in improving the storage density (and thus capacity) of disk drives.

The technical rationale for using sealed HDAs has several parts, but an important one is as follows. To maximize storage density, the head must be 'flown' as close to the surface of the platter as possible; at such heights, even tiny dust particles can cause a [[head crash]]. If outside air is being introduced, it is difficult to filter out the smallest particles; and in any event, the filters must be replaced regularly, a maintenance headache. Sealing the HDA in a 'clean room' environment avoids these problems.

It was later discovered that filling the HDA with helium was advantageous, due to its lower density.

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==External links==

* [https://patents.google.com/patent/US3786454A/en Magnetic disk storage apparatus] - The basic sealed HDA patent
* [https://patents.google.com/patent/US3973273A/en Magnetic disk storage apparatus]
* [https://patents.google.com/patent/US4034411A/en Magnetic disk information storage apparatus]
* [https://www.seagate.com/files/www-content/product-content/enterprise-hdd-fam/enterprise-capacity-3-5-hdd-10tb/_shared/docs/helium-drive-launch-tp686-1-1602us.pdf Decades of Proven Research Underpin Seagate’s Helium Drive]
* [https://www.computerhistory.org/collections/catalog/102626588 DEC Head Disk Assembly (HDA)]
* [https://www.computerhistory.org/revolution/memory-storage/8/259/1066 DEC Head Disk Assembly (HDA)]
* [https://www.pdp-11.nl/peripherals/disk/ra-images/ra81-open-model.jpg RA81 HDA] - fantastic image of a sectioned [[RA81]] HDA

[[Category: Device Basics]]