Advanced Disc Filing System: Difference between revisions

Revision as of 09:47, 26 April 2016

Revision as of 04:15, 27 April 2016

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==8-bit usage==

ADFS on 8-bit systems required a WD1770 or later 1772-series floppy controller, owing to the inability of the original Intel 8271 chip to cope with the double-density format ADFS required. ADFS could however be used to support hard discs without a 1770 controller present; in development the use of hard discs was the primary goal, extension to handle floppies came later. The 1770 floppy controller was directly incorporated into the design of the Master Series and B+ models{{Citation needed|date=June 2007}}, and was available as an 'upgrade' board for the earlier Model B. The Acorn Electron's floppy interface (Acorn Plus 3) was an add-on unit, initially available through Acorn and later Pres (aka Advanced Computer Products). The ACP implementation of ADFS fixed a flaw in the Acorn version v1.0, that required the use of a file named ZYSYSHELP. On the [[Acorn_ElectronAcorn Electron#ADFS_quirksADFS quirks|Electron]], Disk corruption could also occur if attempting to use the <tt>*COMPACT</tt> command without disabling the blinking cursor. This was due to the fact that the <tt>*COMPACT</tt> command used screen memory as working space during the operation, and the blinking cursor corrupted that memory space.<ref>http://www.portices.fr/formation/Res/Info/Dimet/Ordinateurs/AcornBBC/www.stairwaytohell.com/Ressources/r-EU-ACP-E00ADFS.html</ref>

ADFS supported hard discs, and 3½" [[floppy disc]]s formatted up to 640&nbsp;KB capacity using double density [[Modified Frequency Modulation|MFM]] encoding (''L'' format; single-sided disks were supported with the ''S'' format (160&nbsp;KB) and ''M'' format (320&nbsp;KB)). ADFS as implemented in the BBC microcomputer system (and later RISC OS) never had support for single-density floppies.

Hard disc support in ADFS used the same format as ''L'' format floppies in terms of 256-byte

blocks;<ref>http://mdfs.net/Docs/Comp/Disk/Format/ADFS ADFS on-disk layout documentation</ref>;

only the underlying arrangement of tracks and sectors differed depending on the actual drive used, but this was managed by the [[Small_Computer_System_InterfaceSmall Computer System Interface|SCSI]] controller. It interfaced to a [[ST-506|ST506/ST412]]-based Winchester unit via the BBC Micro's 1&nbsp;MHz Bus, an Acorn-designed interface card (1&nbsp;MHz Bus to SCSI adapter) and an off-the-shelf [[Adaptec]] SCSI controller (SCSI to ST-506 adapter).

Support for [[Advanced Technology Attachment|IDE]]/[[ATAPI]] style drives has been added 'unofficially' by third parties in recent years.<ref>[http://mdfs.net/Info/Comp/BBC/IDE BBC IDE Interface]</ref>