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== Features == === OS core === The OS is [[single-user]] and employs [[cooperative multitasking]] (CMT).<ref name="byte tired">{{cite journal |url=https://archive.org/details/eu_BYTE-1996-12_OCR/page/n84/mode/1up |title=A RISC OS for All Seasons |last=Palmer |first=Stewart |journal=[[Byte (magazine)|Byte]] |date=December 1996 |volume=21 |issue=12 |page=49 |oclc=208951251 |issn=0360-5280}}</ref> While most current desktop OSes use [[preemption (computing)|preemptive]] [[computer multitasking|multitasking]] (PMT) and [[thread (computer science)|multithreading]], {{nowrap|RISC OS}} remains with a CMT system. By 2003, many users had called for the OS to migrate to PMT.<ref name="drobe williams pmt 2003">{{cite news|last=Williams|first=Chris|title=Imagining RISC OS and PMT|url=http://www.drobe.co.uk/article.php?id=764|access-date=10 July 2012|newspaper=[[Drobe]]|date=26 July 2003|archive-date=17 June 2018|archive-url=https://web.archive.org/web/20180617115807/http://www.drobe.co.uk/article.php?id=764|url-status=live}}</ref> The OS [[memory protection]] is not comprehensive.<ref>Michael Reed [https://books.google.com/books?id=Lr8ldHhh_wsC&pg=PA82 ''Tech Book 1'' – Published articles Oct 2006 – June 2008] {{Webarchive|url=https://web.archive.org/web/20200726094727/https://books.google.es/books?id=Lr8ldHhh_wsC&pg=PA82 |date=26 July 2020 }}</ref><ref>{{cite web|url=http://www.drobe.co.uk/riscos/artifact1327.html|title=RISC OS Memory Protection|website=Drobe: The Archives|access-date=4 March 2013|archive-date=31 March 2014|archive-url=https://web.archive.org/web/20140331035623/http://www.drobe.co.uk/riscos/artifact1327.html|url-status=live}}</ref> The core of the OS is stored in [[read-only memory|ROM]], giving a fast [[bootup]] time and safety from operating system corruption. RISC OS 4 and 5 are stored in {{nowrap|4 MB}} of [[flash memory]], or as a [[ROM image]] on [[SD card]] on single board computers such as the Beagleboard or Raspberry Pi, allowing the operating system to be updated without having to replace the ROM chip. The OS is made up of several [[Loadable kernel module|module]]s. These can be added to and replaced, including soft-loading of modules not present in ROM at run time and on-the-fly replacement. This design has led to OS developers releasing rolling updates to their versions of the OS, while third parties are able to write OS replacement modules to add new features. OS modules are accessed via software interrupts (SWIs), similar to [[system call]]s in other operating systems. Most of the OS has defined [[application binary interface]]s (ABIs) to handle filters and vectors. The OS provides many ways in which a program can intercept and modify its operation. This simplifies the task of modifying its behaviour, either in the GUI, or deeper. As a result, there are several third-party programs which allow customising the OS look and feel. === File system === {{More citations needed section|date=July 2017}} The [[file system]] is volume-oriented: the top level of the file hierarchy is a volume (disc, network share) prefixed by the file system type. To determine [[file type]], the OS uses [[metadata]] instead of [[file extension]]s. Colons are used to separate the file system from the rest of the path; the root is represented by a dollar (<code>$</code>) sign and directories are separated by a full stop (<code>.</code>). Extensions from foreign file systems are shown using a slash (<code>example.txt</code> becomes <code>example/txt</code>).<ref name="drobe naulls 2004">{{cite web |url=http://www.drobe.co.uk/article.php?id=921 |title=RISC OS filename translation |work=[[Drobe]] |date=2 January 2004 |access-date=25 April 2012 |last=Naulls |first=Peter |archive-date=9 July 2011 |archive-url=https://web.archive.org/web/20110709035738/http://www.drobe.co.uk/article.php?id=921 |url-status=live }}</ref> For example, <code>ADFS::HardDisc4.$</code> is the root of the disc named ''HardDisc4'' using the [[Advanced Disc Filing System]] (ADFS) file system. {{nowrap|RISC OS}} filetypes can be preserved on other systems by appending the hexadecimal type as '<code>,xxx</code>' to filenames.<ref name="drobe naulls 2004" /><ref name="osnews round 2004">{{cite web|url=http://www.osnews.com/story/6170/Emulating_RISC_OS_under_Windows/page3/|title=Emulating RISC OS, Page 3/3|website=[[OSNews]]|access-date=25 April 2012|archive-date=13 March 2012|archive-url=https://web.archive.org/web/20120313042944/http://www.osnews.com/story/6170/Emulating_RISC_OS_under_Windows/page3/|url-status=live}}</ref> When using [[cross-platform]] software, filetypes can be invoked on other systems by naming appending '<code>/[extension]</code>' to the filename under {{nowrap|RISC OS}}.<ref name="archive fitton 1994">{{citation |last=Fitton |first=Gerald |date=August 1994 |title=Fireworkz for Windows |periodical=[[Archive (magazine)|Archive]] |publisher=Abbey Press |location=Glastonbury |volume=7 |issue=11 |page=21 |url=http://downloads.abacusline.me.uk/pdf/Arc/2007/GC0701.pdf |oclc=222434223 |access-date=25 April 2012 |archive-date=3 December 2013 |archive-url=https://web.archive.org/web/20131203024536/http://downloads.abacusline.me.uk/pdf/Arc/2007/GC0701.pdf |url-status=live }}</ref> A file system can present a file of a given type as a volume of its own, similar to a [[loop device]]. The OS refers to this function as an image filing system. This allows transparent handling of archives and similar files, which appear as directories with some special properties. Files inside the image file appear in the hierarchy underneath the parent archive. It is not necessary for the archive to contain the data it refers to: some symbolic link and network share file systems put a reference inside the image file and go elsewhere for the data. The file system abstraction layer [[Application programming interface|API]] uses 32-bit file offsets, making the largest single file 4 [[Gibibyte|GiB]] (minus 1 byte) long. However, prior to RISC OS 5.20 the file system abstraction layer and many RISC OS-native file systems limited support to 31 bits (just under 2 GiB) to avoid dealing with apparently negative file extents when expressed in [[two's complement]] notation.{{citation needed|date=July 2017}} === File formats === {{Main|List of RISC OS filetypes}} The OS uses [[metadata]] to distinguish [[file format]]s. Some [[list of file formats|common file formats]] from other systems are mapped to filetypes by the MimeMap module.<ref name="iyonix">{{cite web|url=http://www.iyonix.com/32bit/MIMEMap.shtml|title=Iyonix: MIMEMap|work=iyonix.com|url-status=dead|archive-url=https://web.archive.org/web/20160303223854/http://www.iyonix.com/32bit/MIMEMap.shtml|archive-date=3 March 2016}}</ref> === Kernel === The RISC OS kernel is single-tasking and controls handling of [[interrupt]]s, [[Direct memory access|DMA]] services, memory allocation and the video display; the cooperative multi-tasking is provided by the WindowManager module.<ref name="byte tired" /> === Desktop === [[File:RISCOS 4 scr.png|thumb|A screenshot of RISC OS 4]] The [[WIMP (computing)|WIMP]] interface is based on a [[stacking window manager]] and incorporates three [[mouse button]]s<ref name="Ryan2011">{{cite book|last=Ryan|first=Dan|title=History of Computer Graphics: DLR Associates Series|url=https://books.google.com/books?id=136myWlKpwEC&pg=PA358|access-date=13 June 2013|date=13 April 2011|publisher=AuthorHouse|isbn=978-1-4567-5115-9|page=358|archive-date=6 July 2014|archive-url=https://web.archive.org/web/20140706155034/http://books.google.com/books?id=136myWlKpwEC&pg=PA358|url-status=live}}</ref> (named ''Select'', ''Menu'' and ''Adjust''), [[context-sensitive user interface|context-sensitive]] menus, window order control (i.e. send to back) and dynamic window [[Focus (computing)|focus]] (a window can have input focus at any position on the stack). The [[icon bar]] ([[Dock (computing)|Dock]]) holds icons which represent mounted disc drives, RAM discs, running applications, system utilities and docked: files, directories or inactive applications. These icons have context-sensitive menus and support [[drag-and-drop]] operation. They represent the running application as a whole, irrespective of whether it has open windows. The GUI functions on the concept of files. The Filer, a [[spatial file manager]], displays the contents of a disc. Applications are run from the Filer view and files can be dragged to the Filer view from applications to perform saves, rather than opening a separate 'Save' dialog box where the user must navigate to a location already visible in the Finder. In addition, files can be directly transferred between applications by dragging a save icon into another application's window. [[Application directories]] are used to store applications. The OS differentiates them from normal directories through the use of an [[Exclamation mark#Computing|exclamation mark]] (also called a ''pling'' or ''shriek'') prefix. Double-clicking on such a directory launches the application rather than opening the directory. The application's executable files and resources are contained within the directory, but normally they remain hidden from the user. Because applications are self-contained, this allows drag-and-drop installing and removing. The {{nowrap|RISC OS}} ''Style Guide'' encourages a consistent [[look and feel]] across applications. This was introduced in {{nowrap|RISC OS 3}} and specifies application appearance and behaviour. Acorn's own main [[#Bundled applications|bundled applications]] were not updated to comply with the guide until {{nowraplinks|[[RISCOS Ltd]]}}'s ''Select'' release in 2001.<ref name="iconbar possibly influential">{{cite web |url=http://www.iconbar.com/articles/Influential/index1152.html |title=An arbitrary number of possibly influential RISC OS things |work=[[The Icon Bar]] |date=23 March 2007 |access-date=27 September 2011 |last=Phil |first=Mellor |quote=Admittedly it wasn't until RISC OS Select was released, almost 10 years later, that the standard Acorn applications (Draw, Edit, and Paint) implemented the style guide's clipboard recommendations, but most products followed it with care. |archive-date=31 March 2012 |archive-url=https://web.archive.org/web/20120331173614/http://www.iconbar.com/articles/Influential/index1152.html |url-status=live }}</ref> === Font manager === RISC OS was the first operating system to provide scalable anti-aliased fonts.<ref>{{cite web |url=http://www.osnews.com/story/6170/Emulating_RISC_OS_under_Windows/page1/ |title=Emulating RISC OS under Windows |access-date=12 May 2011 |last=Round |first=Mark |date=26 February 2004 |work=OSnews |quote=Many of the UI concepts that we take for granted were first pioneered in RISC OS, for instance: scalable anti-aliased fonts and an operating system extendable by 'modules', while most of the PC world was still on Windows 3.0. |archive-date=14 November 2010 |archive-url=https://web.archive.org/web/20101114004250/http://www.osnews.com/story/6170/Emulating_RISC_OS_under_Windows/page1/ |url-status=live }}</ref><ref>{{cite web |url=http://telcontar.net/Misc/GUI/RISCOS/ |title=The RISC OS GUI |access-date=12 May 2011 |last=Ghiraddje |date=22 December 2009 |publisher=Telcontar.net |quote=Only with Mac OS X did any mainstream graphical interface provide the smoothly rendered, fractionally spaced type that Acorn accomplished in 1992 or earlier. |archive-date=16 July 2011 |archive-url=https://web.archive.org/web/20110716233538/http://telcontar.net/Misc/GUI/RISCOS/ |url-status=live }}</ref><ref>{{cite web |url=https://arstechnica.com/old/content/2005/05/gui.ars/6 |title=A History of the GUI |access-date=25 May 2011 |first=Jeremy |last=Reimer |date=May 2005 |publisher=[[ArsTechnica]] |quote=[...] in 1987, the UK-based company Acorn Computers introduced their [...] GUI, called "Arthur", also was the first to feature anti-aliased display of on-screen fonts, even in 16-color mode! |archive-date=2 December 2011 |archive-url=https://web.archive.org/web/20111202061840/http://arstechnica.com/old/content/2005/05/gui.ars/6 |url-status=live }}</ref><ref>{{cite web |url=http://www.osnews.com/story/21713/Screen_Fonts_Shape_Accuracy_or_On-Screen_Readability_ |title=Screen Fonts: Shape Accuracy or On-Screen Readability? |access-date=13 June 2011 |first=Thom |last=Holwerda |date=23 June 2005 |publisher=[[OSNews]] |quote=[...] it was RISC OS that had the first system-wide, intricate [...] font rendering in operating systems. |archive-date=19 November 2011 |archive-url=https://web.archive.org/web/20111119223926/http://www.osnews.com/story/21713/Screen_Fonts_Shape_Accuracy_or_On-Screen_Readability_ |url-status=live }}</ref> Anti-aliased fonts were already familiar from Arthur, and their presence in RISC OS was confirmed in an early 1989 preview,<ref name="PCW 1989-01">{{cite news | first1=Dick | last1=Pountain | title=Screentest: Archie RISC OS | work=[[Personal Computer World]] | date=January 1989 | url=http://chrisacorns.computinghistory.org.uk/docs/Mags/PCW/PCW_Jan89_RISCOS.pdf | page=154 | access-date=4 March 2021 | quote=[ArcDraw] can also add text in multiple sizes and fonts to a drawing (including anti-aliased fonts) | archive-date=13 June 2021 | archive-url=https://web.archive.org/web/20210613044349/http://chrisacorns.computinghistory.org.uk/docs/Mags/PCW/PCW_Jan89_RISCOS.pdf | url-status=live }}</ref> featuring in the final RISC OS 2 product, launched in April 1989.<ref name="acornuser198902">{{ cite news | url=https://archive.org/details/AcornUser079-Feb89/page/n10/mode/1up | title=RISC OS is ready for April launch | work=Acorn User | date=February 1989 | access-date=31 October 2020 | pages=9 }}</ref> A new version of the font manager employing "new-style outline fonts" was made available after the release of RISC OS,<ref name="acornuser198904_fonts">{{ cite news | url=https://archive.org/details/AcornUser081-Apr89/page/n8/mode/1up | title=New fonts for DTP | work=Acorn User | date=April 1989 | access-date=3 May 2021 | pages=7 }}</ref> offering full support for the printing of scalable fonts, and was provided with Acorn Desktop Publisher.<ref name="acornuser198910">{{ cite news | url=https://archive.org/details/AcornUser087-Oct89/page/n135/mode/2up | title=Hold the Font Page | work=Acorn User | date=October 1989 | access-date=14 April 2021 | last1=Bell | first1=Graham | pages=134–135 }}</ref> It was also made available separately and bundled with other applications.<ref name="acornuser199004_font">{{ cite news | url=https://archive.org/details/AcornUser093-Apr90/page/n20/mode/1up | title=Acorn Customer Hotline | work=Acorn User | date=April 1990 | access-date=2 May 2021 | pages=19 }}</ref> This [[outline font]] manager provides support for the rendering of font outlines to bitmaps for screen and printer use, employing [[spatial anti-aliasing|anti-aliasing]] for on-screen fonts, utilising sub-pixel anti-aliasing and caching for small font sizes.<ref name="raine1991">{{ cite conference | url=https://archive.org/details/1989-proceedings-5th-comp-graphics-workshop/page/25/mode/1up | title=The Acorn Outline Font Manager | last1=Raine | first1=Neil | last2=Seal | first2=David | last3=Stoye | first3=William | last4=Wilson | first4=Roger | conference=Fifth Computer Graphics Workshop | location=Monterey, California | date=November 1989 | publisher=USENIX Association | pages=25–36 }}</ref> At the time of the introduction of Acorn's outline font manager, the developers of rival desktop systems were either contemplating or promising outline font support for still-unreleased products such as Macintosh [[System 7]] and [[OS/2]] version 2.<ref name="acornuser198911_mytype">{{ cite news | url=https://archive.org/details/AcornUser088-Nov89/page/n69/mode/2up | title=My Type | work=Acorn User | date=November 1989 | access-date=7 May 2021 | last1=Bell | first1=Graham | pages=68–69 }}</ref> From 1993, starting with the German RISC OS 3.12, and in 1994 for RISC OS 3.5, it has been possible to use an outline anti-aliased font in the WindowManager for UI elements, rather than the [[Bitmap fonts|bitmap system font]] from previous versions.<ref>{{cite magazine | date = July 1993 | title = Acorn signs pre-press deal | url = https://archive.org/details/AcornUser132-Jul93/page/n11/mode/2up | magazine = [[Acorn User]] | page = 10 | publisher = [[Addison-Wesley]] | access-date = }}</ref><ref name="acorn_an253">{{ cite tech report | url=http://chrisacorns.computinghistory.org.uk/docs/Acorn/AN/253.pdf | title=Acorn Computers Support Group Application Notice 253 – New features of RISC OS version 3.5 | publisher=Acorn Computers Limited | last1=Murphy | first1=Dean | date=29 March 1994 | access-date=2 March 2022 | issue=0.02 }}</ref> RISC OS 4 does not support [[Unicode]] but "RISC OS 5 provides a Unicode Font Manager which is able to display Unicode characters and accept text in [[UTF-8]], UTF-16 and UTF-32. Other parts of the RISC OS kernel and core modules support text described in UTF-8."<ref>{{cite web|url=http://www.riscos.info/index.php/Unicode_in_RISC_OS|title=Unicode in RISC OS|work=riscos.info|access-date=28 April 2015|archive-date=11 April 2015|archive-url=https://web.archive.org/web/20150411221409/http://www.riscos.info/index.php/Unicode_in_RISC_OS|url-status=live}}</ref><!-- There are two issues: 1) Printing Unicode to a PostScript printer will break as PDriverPS just embeds the Fonts:Encodings.UTF8 encoding file directly in the PS output. This file is not valid PostScript. 2) Printing UTF-16 or UTF-32 to any printer driver will fail as they're not expecting anything other than an 8-bit encoding.[..] Issue 1 can be avoided by using the PostScript 3 printer driver (instead of using the native RISC OS PostScript printer driver) which was developed by John Tytgat and Martin Würthner. The ROOL project has released updated Printer Manager software which fixes issue 2.--> Support for the characters of RISC OS (and some other historic computers) was added to [[Unicode]] 13.0 (in 2020).<ref>{{Cite web|url=https://www.unicode.org/versions/Unicode13.0.0/ch22.pdf|title=The Unicode® Standard Version 13.0 – Core Specification|access-date=11 March 2020|archive-date=6 May 2021|archive-url=https://web.archive.org/web/20210506122306/https://www.unicode.org/versions/Unicode13.0.0/ch22.pdf|url-status=live}}</ref> === Bundled applications === {{Main|List of RISC OS bundled applications}} {{nowrap|RISC OS}} is available in several distributions, all of which include a small standard set of [[desktop application]]s, but some of which also include a much wider set of useful programs. Some of those richer distributions are freely available, some are paid for.
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