Advanced Disc Filing System: Difference between revisions

Revision as of 20:06, 11 December 2020

Revision as of 23:12, 6 March 2021

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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.{{cn|date=March 2021}} The 1770 floppy controller was directly incorporated into the design of the Master Series and B+ models,<ref name="acornuser198507">{{Citation needed|date=Junecite 2007}},news and| wasurl=https://archive.org/details/AcornUser036-Jul85/page/n161/mode/2up available as an 'upgrade' board for the earlier Model| title=B.+ TheGrading Acorn| Electron's floppy interface (work=Acorn PlusUser 3)| wasdate=July an1985 add| access-ondate=18 unit,October initially2020 available| throughlast1=Smith Acorn| andfirst1=Bruce later| Prespages=160–161 (aka}}</ref> Advancedand Computerwas Products).available as Thean ACPupgrade implementationboard of ADFS fixed a flaw infor the Acornearlier versionModel v1B.0,<ref thatname="1770_disc_interface">{{ requiredcite thebook use of a file| named ZYSYSHELPurl=http://chrisacorns. On the [[computinghistory.org.uk/docs/Acorn/Misc/Acorn_1770DiscIF.pdf Electron#ADFS quirks|Electron]], Disktitle=1770 corruptionDisc couldInterface also| occurpublisher=Acorn ifComputers attemptingLimited to| useaccess-date=6 theMarch <tt>*COMPACT2021 }}</ttref> commandADFS withoutcould disablingbe the blinking cursor. This was dueadded to theModel fact that the <tt>*COMPACT</tt> command used screen memory as working space during the operation,B and theB+ blinkingsystems cursorwith corrupted thatan memoryadditional spaceupgrade.<ref name="adfs_upgrade">{{ cite webbook | url=http://wwwchrisacorns.computinghistory.porticesorg.fruk/formationdocs/Res/Info/Dimet/OrdinateursAcorn/AcornBBCMisc/wwwAcorn_ADFSUpgrade.stairwaytohell.com/Ressources/r-EU-ACP-E00ADFS.htmlpdf | title=Stairwaytohell.ComADFS -upgrade Hardware| |websitepublisher=Portices.frAcorn Computers Limited | access-date=2016-08-016 March 2021 }}</ref>

The [[Acorn Electron#Acorn Plus 3|Acorn Plus 3]], Acorn's official disc expansion for the Acorn Electron, was supplied with ADFS as standard, but this implementation featured various notable bugs. A file called {{mono|ZYSYSHELP}} was "required by the system" and created during formatting.<ref name="plus3ug">{{ cite book | url=http://chrisacorns.computinghistory.org.uk/docs/Acorn/Manuals/Acorn_Plus3UG.pdf | title=The Electron Plus 3 User Guide | publisher=Acorn Computers Limited | date=October 1984 | issue=1 | access-date=6 March 2021 }}</ref>{{rp|pages=7}} This was a kludge. Acorn's original ADFS implementation on the Electron was unreliable when writing to the first few tracks of a floppy disc, so this was a "fix" and simply involved writing a file full of garbage to the suspect part. The ADFS would then skip it.{{cn|date=March 2021|reason=This is apparently true, but a source would be helpful.}} Disc corruption could also occur if attempting to use the {{kbd|*COMPACT}} command without disabling the blinking text cursor.<ref name="electronuser198808">{{ cite news | url=https://archive.org/details/ElectronUserVolume5/Electron-User-05-11/page/n8/mode/1up | title=Improving on perfection | work=Electron User | volume=5 | issue=11 | date=August 1988 | access-date=20 January 2021 | last1=Waddilove | first1=Roland | pages=9 }}</ref><ref group=note>This was due to the fact that the {{kbd|*COMPACT}} command used screen memory (by default) as working space during the operation, and the software-implemented blinking cursor corrupted that memory space. An alternative would be to give arguments to make it use non-screen memory for workspace, for example {{kbd|*COMPACT 40 20}} in screen mode 6. On the BBC Micro, the blinking cursor, if enabled, was superimposed onto the display output by the 6845 CRTC and Acorn's video ULA, without changing any screen memory. The Acorn Electron did not have this extra hardware and had to alter screen memory in software to blink the cursor.</ref> Hugo Tyson, principal ADFS developer, recalls that this bug was found during late testing but not fixed in the initial ROM release in order to avoid late changes, as workarounds exist.

On the Electron, disc formatting was done via the {{kbd|*EFORM}} command instead of the established {{kbd|*FORM40}}/{{kbd|*FORM80}} DFS commands. Note additionally that the {{kbd|*EFORM}} command differs from the equivalent {{kbd|*AFORM}} command for the 1770 ADFS on the BBC Microcomputer. This is possibly as a result of needing to create the {{mono|ZYSYSHELP}} file on the Electron. The {{kbd|*EFORM}} command was only supplied on the Welcome disc that was shipped with the Plus3, and was not included in the ROM.<ref name="plus3ug" />{{rp|pages=48}}

ADFS supported hard discs, and 5¼" [[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.

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Support for [[Advanced Technology Attachment|IDE]]/[[ATAPI]] style drives has been added 'unofficially' by third parties in recent years.<ref>{{cite web|url=http://mdfs.net/Info/Comp/BBC/IDE |title=BBC IDE Interface - MDFS::Info.Comp.BBC.IDE |website=MDFS.net |access-date=2016-08-01}}</ref>

The ADFS file format used the ascii bytes {{mono|[[Advanced Disc Filing System|Hugo]]}} to delimit the directory names on the disc, named after ADFS author Hugo Tyson.

==32-bit usage (Arthur and RISC OS)==