RISC OS

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Acorn's 32bit Operating System for ARM CPUs has gone through many changes in the nearly 20 years since its launch. It's name has changed from Arthur to RISC OS to NCOS, and its owners have changed from Acorn to Element 14(?) to Pace to Castle. This is a brief record of the different versions of which I have copies. There are other versions, mainly softloaded development versions (including EPROMed versions for the A500), for details of these and more details in general see Matthias Seifert's Software Evolutions.

AuthorOS NameOS
Version
Date of
Utility
Module
OS
Identifier
ROM Part
Number
Comments
AcornArthur0.3017 Jun 1987&A00276,322-01
0276,323-01
0276,324-01
0276,325-01
A305, A310
AcornArthur1.10   A300 service manual ROM fitting
instructions: The ROM set
numbered 1, 2, 3 and 4
although labelled Arthur 1.1 is in
fact Arthur 1.2
AcornArthur1.2025 Sep 1987&A00277,022-02
0277,023-03
0277,024-02
0277,025-02
A440
AcornRISC OS2.0005 Oct 1988&A10283,022-01
0283,023-01
0283,024-01
0283,025-01
A3000 & A4x0/1
AcornRISC OS2.0105 Jul 1990&A20270,601-01
0270,602-01
0270,603-01
0270,604-01
A540 and R260
AcornRISC OS2.06??n/aDevelopment version
for ARM3 A500
AcornRISC OS3.0025 Sep 1991&A30270,251-01
0270,252-01
0270,253-01
0270,254-01
early A5000
AcornRISC OS3.1030 Apr 1992&A44 ROM Set
0296,041-01
0296,042-01
0296,043-01
0296,044-01 
 
AcornRISC OS3.1030 Apr 1992&A42 ROM Set
0296,061-01
0296,062-01
A4
Extension ROM (0296-063-01)
with Power management module
AcornRISC OS3.1129 Sep 1992&A44 ROM set:
0296,041-02
0296,042-02
0296,043-02
0296,044-02
 
AcornRISC OS3.1129 Sep 1992&A42 ROM set:
0296,061-02
0296,062-02
A3010, A3020 & A4000
AcornRISC OS3.1909 Jun 1993&A40296,241-01
0296,242-01
0296,243-01
0296,244-01
German RISC OS 3.11
AcornRISC OS3.5018 Feb 1994&A50297,521-01
0297,522-01
RiscPC 600
AcornRISC OS3.6013 Apr 1995&A61203,101-01
1203,102-01
RiscPC 700
AcornRISC OS3.611 Aug 1995&A61206,520
1206,521
AOM STB2
AcornRISC OS3.7030 Jul 1996&A71203,191-01
1203,192-01
StrongARM support
AcornRISC OS3.7119 Feb 1997&A71203,261-01
1203,262-01
 
AcornRISC OS3.8028 Apr 1998&A71203,364-01softloaded
Development version for Pheobe
Only released to developers
RISCOS LtdRISC OS4.00?&A8?Initial release
sold at RISCOS SE Show July 99
RISCOS LtdRISC OS4.01?&A8?Sold july-Aug 99
RISCOS LtdRISC OS4.0210 Aug 1999&A819990818-001Final release
RISCOS LtdRISC OS4.0309 Nov 1999&A819991214-001RiscStation
RISCOS LtdRISC OS4.0309 Nov 1999&A820000330-002Microdigital Mico
RISCOS Ltd RISC OS4.03?&A8?Castle Kinetic Risc PC
RISCOS LtdRISC OS4.04?&A8?Castle Kinetic Risc PC 300MHz
RISCOS Ltdembedded
RISC OS
4.068 Jan 2003&A820030120-002Orpheus
development version
RISCOS LtdRISC OS4.2923 Apr 2002&A920020428-001soft-loaded
RISC OS Select Issue 1 Release 9
RISCOS LtdRISC OS4.3330 Oct 2002&A920021118-001soft-loaded
RISC OS Select 2 Issue 3
RISCOS LtdRISC OS4.3711 Aug 2003&A920030915-001soft-loaded
RISC OS Select 3 Issue 3
RISCOS LtdRISC OS4.3910 Mar 2004&A920040317-001RISC OS Adjust 1 Issue 1
RISCOS LtdRISC OS4.3928 Apr 2004&A920040510-003soft-loaded
RISC OS Select 3 Issue 4
RISCOS LtdRISC OS4.40n/a&A9n/aAdjust32 for A9home, 1st release
RISCOS LtdRISC OS4.41n/a&A9n/aAdjust32 for A9home, 2nd release
RISCOS LtdRISC OS4.4215 Mar 2006&A920060316-002Adjust 32 for A9home retail version
AcornNCOS1.0626 Oct 1996 2203,021-01
2203,022-01
OS Version Module
Version 4.50
Date 08 Nov 1996
AcornNCOS1.1126 Oct 1996 2203,222-01
2203,223-01
OS Version Module
Version 4.50
Date 24 Feb 1998
PaceRISC OS-NC5.1326 Jan 2000&A72208,670
2208,671
OS Version Module
Version 5.13
Date 19 Oct 1999
Bush Internet Surf Set IBX-100
PaceRO-STB4.0.025 Sep 2000  OS Version Module 5.30
Date 28 June 2000
Build STB4001910
Pace DSL4000
CastleRISC OS5.03 &AAFlash ROMCastle Iyonix
CastleRISC OS5.0517 Feb 2004&AAFlash ROMCastle Iyonix
CastleRISC OS5.06 &AAFlash ROMCastle Iyonix
CastleRISC OS5.07 &AAFlash ROMCastle Iyonix
CastleRISC OS5.0804 Nov 2004&AAFlash ROMCastle Iyonix
CastleRISC OS5.0918 May 2005&AAFlash ROMCastle Iyonix
CastleRISC OS5.107 Oct 2005&AAFlash ROMCastle Iyonix
CastleRISC OS5.1122 Feb 2006&AAFlash ROMCastle Iyonix 
CastleRISC OS5.1226-Jun-06&AAFlash ROMCastle Iyonix
CastleRISC OS5.1323-Feb-07&AAFlash ROMCastle Iyonix
RISC OS OpenLtdRISC OS5.14  Flash ROMsoft-loaded or Flash ROM.
Castle Iyonix
RISC OS Open LtdRISC OS5.1618 Jan 2010&AAFlash ROM soft-loaded or Flash ROM.
Castle Iyonix
RISCOS LtdRISC OS6.0208 Oct 2006&A920061024-iii-virginiaPreview. Select 4i1
RISCOS LtdRISC OS6.0619 Mar 2007&A920070424-001soft-loaded. Select 4i2
RISCOS LtdRISC OS6.1020 Apr 2008&A920080422-001soft-loaded. Select 4.4
RISCOS LtdRISC OS6.141 Dec 2008&A920081201-001soft-loaded. Select 5i1
RISC OS LtdRISC OS6.1619 Apr 2009&A920090419-001soft-loaded. Select 5i2

Images of some of these ROMs are available from Tribbeck.com, but please note the copyright.