ISIS, Intellec, PL/M, iRMX, and Intel - 21st century

Most recent revision dated Dec 18 2023. (c)Copyright Herb Johnson 2023.

This document references an earlier description I wrote, about the earliest Intel 4-bit and 8-bit development systems and their software; as part of my interests in Digital Research. There's also information in that document, about subsequent ownership of these INtel early products after Intel sold off the rights. This Web page only, has Web links to sites with more and current ISIS and Multibus information and current developments and software.

I developed the original document back in 2009, as part of my interests in early Digital Research, a company founded by Dr. Gary Kildall, to produce and sell CP/M. KIldall developed Intel's PL/M and created some of Intel's FORTRAN based cross-assemblers for the 8008 and 8080. But in 2007 and later, I worked on Intel Multibus systems myself (and with Bill Beech), and I wrote more Web pages about Intel's Multibus and about ISIS. In 2015 and later, additional people became active in Intel's old 8-bit development systems, putting that old stuff back to use and bringing it into the 21st century.

So in 2016 I've split that early Intel ISIS page. I'll keep among the Digital Research pages, the early history of Intel's development systems and the subsequent ownership of that property. It's pretty static stuff. I've put some of that information on this Web page. But only on this Web page, will be the links and discussions of relatively recent ISIS and Multibus work, as part of my "restoration" part of my Web site. Several people are restoring Multibus and ISIS systems since 2016.

- Herb Johnson

20th C. ISIS Web page:

  • Background
  • Before the 8080 and Multibus
  • ISIS II operating system
  • ISIS operating system
  • PL/M
  • ISIS and Multibus ownership
  • iRMX ownership

    this 21st C. ISIS Web page:

  • Background
  • Current work and correspondence
  • Running ISIS or iRMX today
  • other PL/M and ISIS Web links


    More information about the early days of Intel's ISIS and Multibus systems are on my DRI ISIS Web page. The information below is a subset of the content of the linked Web page.

    A version of ISIS was produced sometime in 1976 by Intel for their Multibus-based, 8080-based "Intellec MDS" system. This was followed by ISIS OS's for other 8080 and later 8086 based systems. Intel's version of the programming language PL/M first supported the 8008, then later the 8080 and subsequent Intel processors. iRMX, not described here, was a later Intel real-time operating system which ran on Intel processors.

    Intel's Multibus standards describes an 86-pin connector with specific signals and a secondary connector, all on a card of standard size. Multibus was designed as a general bus standard and product; it became an IEEE standard.

    PL/M-8 and later PL/M-80 were FORTRAN-based cross complier running on minicomputers and mainframes. Intel's early product development tools ran either as cross-products or as paper-tape or ROM-based native products. Then Intel developed a floppy-disk controller and the ISIS OS to run those tools, eventually including PL/M compilers. Later Intel provided PL/M and other tools under MS-DOS. I have much more to say about PL/M, and these and other references, in my Web page on the history of Gary Kildall and Digital Research..

    On another Web page about Intel's M2FM, I referenced and discussed some early Intel Multibus floppy-disk controllers and documents. Intel implemented FM and M2FM on their early double-density floppy controllers as a two-board set. Here's a "field guide" document for Intel's earliest Multibus floppy controllers, which I'll refine over time.

    Also: Intel provided ISIS-II on their later portable PDS-100 development system, running on a stacked-board 8085.

    iRMX was an Intel software product, a real-time operating system, implmented on a number of Intel 80286 and 80386 Multibus systems. It saw a modest amount of use in the 80's and into the 1990's. Some remnants of that work has become available in the 21st century.

    Who owns/owned these Intel software tools?

    See my DRI ISIS Web page, for a trail I followed about the successive owners of Intel's Multibus and ISIS and other 8-bit (and 4-bit) development products.

    Current work and email lists after 2016

    Google group: SInce mid-2020, a number of the Intel Multibus ISIS people as I list below, are in discussion on a Google Groups list "intel-devsys" They talk about Intel Multibus systems work, recovering Intel's development systems software and hardware.

    From about 2016 and into 2020 Bill Beech, Richard Main, Eric Smith, myself and others corresponded on use, deconstruction and archiving of additional ISIS and Intel disks and Intel programs; as well as restoration of Intel development systems running ISIS and other OSs. Richard Main in 2016 produced an archive at which in 2017 became unavailable. Bill Beech migrated that archive to his site or to a shared Google drive. Other persons in that email discussion are also working with ISIS images and Intel software tools, some have Web sites or archives. From 2016-20, there's been tremendous progress on "reclaiming" Intel's ISIS and early Multibus-based software. Links and references are below.

    specfic people and details

    In Feb 2019, I was contacted by Mark Alexander, responding to an old on this Web page, about his prior. Mark explains: "I recently updated my ISIS-II simulator work on 64-bit Linux (it previously on worked only on 32-bit systems, due to the 8080 simulator being written in assembly language). It's [on this archive site page]. I don't remember the discussion [you previously] referenced, but in 2003 I found copies of the Intel 8080 tools (PL/M compiler, assembler, etc.) on Intel's web site. My [MS-DOS] simulator was originally written for a little startup (which went defunct pretty quickly), so that they could run the PL/M-86 compiler on the new IBM PC. Since then I've kept it running just for fun; I don't have a real need for it otherwise. I have copies of those [Intel] tools in my git repository. It's a good thing too, since it seems that Intel has deleted them from their site."

    "In any case, you might want to add a link to my git repository to your page, though it appears that John Elliott has written something similar that might be more robust, or at least more portable, since it doesn't appear to depend on assembly language." - Mark

    Curiously, in 2014 I curated this Web page which links ISIS-II and development of some original IBM-PC software. The information from an "OS/2 Museum" Web site, also references Mark's simulator; the Museum site also provided some ISIS disk-image tools. - Herb

    In 2015-16, Bill Beech and others worked with Richard Main on Intel ISIS-II development systems Richard Main was a former Multibus developer; he returned to work on Intel Mulibus development systems, bringing them into the 21st century. Unfortunately, by late 2017 Richard Main was no longer working on these systems and his site is unavailable. Look for "ISIS-MDS.COM" on YouTube, for any surviving videos.

    Bill Beech has worked since about 2015, on restoring multiple Intel Multibus systems; based on his Multibus work from decades prior. Bill Beech's archive results are on Bill Beech's Web site for Multibus and related vintage computers. Bill has his ISIS-related software tools on this Web page among other software tools. The ISIS diskette format schemes are on this Web page. Links may change over time, if so check this Web page I keep for that purpose.

    I have several Web pages about Bill's work in discussion with me, some with links to his pages. I suggest using a Web search engine ("google it") on my site, with the search string "[whatever]"; Or do the same on Bill's site, with "[whatever]".

    Bill Beech's Google drive named "Intel_Devel" archives several people's works. Bill invited individuals to share that drive on June 29th 2018. He's archived the Intel recovery work of a number of people listed on this Web page. You will have to contact Bill about access to his Google drive.

    Eric Smith in 2018 said "I've successfully extracted Intel M2FM ISIS-II files from Kyroflux images using two of my own Python software, fluxtoimd to convert from Kyroflux (or DiscFerret) flux-transition images to ImageDisk images, and isisutils to extract the ISIS-II files from the ImageDisk image." Eric has done substantial work on deconstructing iSBC 215 firmware, ISIS-II diskette images, and more; see his other Intel-related folders on his github site.

    Roger Arrick obtained in 2017 an MDS-800 system with a hard drive (MDS-888) and an advanced version of ISIS called "OSIRIS". Roger's OSIRIS system, methods and files are described on his Web site. He describes how KERMIT may be useful for ISIS serial file transfers to modern computers. If you have trouble with that, check my Web page about USB serial devices and serial file transfers on a vintage microprocessor.

    In Jan 2018, Roger Arrick set up a Facebook account on Intel Intellec and MDS systems. Many of my Multibus friends won't be part of that "social media" activity, but others may, it's an experiment.

    Martyn Vale has some YouTube videos on Intel MDS-800 repair and disk imaging, since late 2019. look for Martyn's Vintage Computing "channel". IN a 2021 post, he said "If you need to create a fresh boot floppy the try my IMG2MDS utility, of course this will only work if the drive / controller is Ok but then if it isnít then a boot disk from anyone wonít work anyway. See this video for an MDS and this video for an MDS II. Nothing is required except a Floppy Disk and a Serial Cable." - Martyn.

    Mark Fisher worked with Series II Intel systems back in the mid-1980's, and ended up with the company's "Blue Box". In 2016 or so he decided to get it running again, and added boards and software, another Intel system, from Ebay. He upgraded himself to a Series III and is working on Ethernet and OSIRIS OS (some later OS release from Intel). As of 2020 I'm not aware of any public presence for Mark Fisher's Multibus work.

    Mark Ogden in 2018 created a github repository of ISIS II related programs. He in said that the "extracted files grouped under their various apps/versions", but they can be regrouped into sets of files "corresponding to the original disk images", see the readme.txt. Contact Mark Ogden if the file service "breaks". Later, Mark Ogden has decompiled "to byte level compatibility" a number of Intel PL/M tools for the ISIS OS and PL/M compiler, as well as several versions of ISIS itself, back to PL/M-80 sources. This a considerable achievement. He has also ported the PL/M tool chain from PL/M to C/C++ sources.

    Check Mark's github repository for those tools. There's an adjacent repository for the PL/M source files. "In addition he has modified John Elliott's ISIS emulator to support several extensions, that make building ISIS / CPM applications with the ISIS toolset simpler.". Also, he's modified a few of Dave Dunfield's imagedisk tools and made some other disk-image tools, to run on under standard C. again, some of these are copied to Bill Beech's Google drive.

    By 2023, Mark Ogden updated and revised his C-language ports of Intel PL/M-80 programs. In Nov 2023 he posted in Google Group "intel-devsys" about further development of these C language tools, and further work on reverse-engineering PL/M based Intel binaries back to PL/M source. He also recompiled, a number of Digital Research Inc. (DRI) 8080 CP/M products also written in PL/M-80. They include BASIC-E, LIB, LINK and TEX, along with the ML80 high level DRI assembler. I exchanged posts with Mark on those DRI software products (BASIC-E was public-domain work). Here's a portion of my exchange that provides some details.

    In Nov 2020, Mark created a repository which he called "a curated set of files taken from many [ISIS or Intel] disk images available on the internet". The site in 2023, consists of mirrors of a few sites which had these materisls; and links which point to Mark's github sites as described above for Mark's own work. A few of Mark's older software tools are still available at this .uk site.

    Al Kossow is working on a number of Multibus systems. There's also his "" archive Web site with a section for Intel MDS disk images. also has documents for Intel board-level and software products. There are mirror sites for that archive site, the home page will list them. There's disk images in IMG (binary) and IMD (Dunfield imagedisk) formats.

    John Hanson has a 8085/Z80 emulator xbeaver, which supports ISIS and the MDS-800. It's based on Nascom and Gemini 80-bus, Z80-based systems once available in the UK and possibly the USA. Seems to be a YAZE derivative (old Z80 emulator), Jon's tool works in the Linux/CentOS world. Jon worked with ISIS (Intel OS) and PL/M in the past, and wanted to run those tools again. John described his emulator in a Jun 1 2018 discussion to me, and there's details on his Web page.

    "xbeaver is a multiboard system originally emulating 80-bus boards (Gemini Computers and others). The boards installed are defined by a configuration file. I have added boards for the MDS-800 Disk controllers to allow the isis code to access emulated disk controllers. Character IO is provided though the bios services I have written to replace the boot/bios rom of the MDS-800. The ISIS system isis_emulator_pack.tar.gz contains hard disk images containing ISIS V4.3 for the beaver emulator."

    Frode van der Meeren contacted me in late 2023, about his restoration and recovery of a Tandberg Data TDV-2114 or 2121 8080 computer produced in Norway. As he described it: "Originally released as an intelligent terminal in 1976, this machine ran Tandberg OS - an operating system designed around the look and feel of Intel ISIS (II?). It even uses the same file system, but different executable file format. The original memory cards in early machines would have 16K of RAM, but most machines that survive (including this one) have a memory card that brings it ujp to 64K total. In Norway it was available until at least 1981. Eventually CP/M was ported to the machine, but I didn't get any disks with CP/M. Siemens would eventually become an OEM producer of this machine, as the "System 6.610". I think they sold it for a longer time than Tandberg." Frode described that he would archive the disks and ROMs and then start repairs.

    ISIS version 1? Here's some initial discussion between myself and Frode about the ISIS-like features of the software. Later he posted some discussion and results in Google Groups intel-devsys. The documents have many links for content. The Tandberg OS apparently looks more like ISIS 1.1 than like the later ISIS-II OS; but likely written in 8080 assembler rather than PL/M-80 (Intel's implementations of ISIS). Siemen's docs for their 6610 are at that link. Frode's github archive for ROMS is there. A TOS 1.81 disk is imaged at this site, mistaken as an ISIS diskette.

    serial to USB flash-drive host

    [usb host]

    Jack McMullen has worked closely with HobbyTronics, on their serial-to-USB-drive device, USB Host Controller Board V2.4, which Richard Main first used with his MDS systems. The current V1.4 Hobbytronics-device firmware is a link for "USB Flash Drive" on that Web page, here's the current link. Caution: this product has been in and out of production over the last years 2017-2020.

    Jack distributes his ISIS-support code by email, and there was a copy on Bill Beech's Google Drive. Here's what I got in Dec 2017. Jack also uses a Hawking H-UC232S serial-to-USB device on his PC, to access the H-T device to update the software on it. Jack has provided me with some details on this stuff. Also look at YouTube videos from Richard Main about the "usb flashdrive", on his old "" on YouTube.

    Here's a July 2018 distribution of the Hobbytronics ISIS-support programs. It is currently incomplete. Jack has a 2018 version of his code on Bill Beech's Google drive "Intel_Devel".

    Jack in mid-2018 was also working hard, on deconstructing how Priam drives work with the isbc215b, trying to reformat various non-ISIS-operated Priam drives.

    Running ISIS or iRMX today


    ISIS was written by Intel to run on Intel Multibus hardware. Unlike CP/M, it doesn't have a hardware-dependent BIOS and a hardware independent BDOS (operating system calls). And different ISIS versions support different sets of Intel Multibus boards, each with their own ROMs and hardware and even processors. So, ISIS was not designed to be hardware portable. Over time however, ISIS and Intel programs under ISIS, have been run on non-Intel hardware or in emulation of Multibus hardware.

    In Apr 2021, Paul Burkel asked about ISIS emulators and pointed out a few of them; as did Mark Ogden and others who work on Intel Multibus restoration. That caused me to update this portion of my Web page. My thanks to Paul, Mark et al. One other point: with ISIS sources available in various forms, one can choose to adjust the source and reassemble (and compile PL/M), rather than just run the original Intel binaries. - Herb


    Intel produced and distributed an ISIS emulator under MS-DOS, to run their various ISIS-based 8080 assemblers and compilers (Fortran80, Pascal80, Cobol80, ASM80). At the intel-vintage archive ,under "Intel Development Software" there's links to download those programs "and ISIS emulator". It runs ISIS-II version 1.0 under MS-DOS.

    My old friend Bill Beech, has various Intel simulators he's written and supported, including work on SIMH V4. SIMH V4 simulates a lot of vintage hardware. Here's the github link to simh V4.X. Apparently SIMH "forked" after version 3.X, one can find other repositories for earlier versions. Also, Bill has disassembled quite a lot of ISIS codes. These are ASM disassemblies, not PL/M.

    There's Udo Munk's Z80pack CP/M emulator for UNIX/Linux systems. He also provides other Z80/8080 operating systems, including ISIS. Look for "ISIS" among his downloads.

    Mark Ogden has decompiled ISIS and a number of Intel tools. look under "/itools/isis/" for original Intel ISIS binaries; and under "/src/" for reconstructed PL/M sources. Also he's ported the PL/M tool chain to C/C++; check his github repository for those tools.

    Mark has also modified and extended John Elliott's THAMES ISIS emulator. He says in disucssion, it "allows ISIS applications to be run but does not emulate full ISIS behaviour. I have enhanced the original version to provide supplementary features to allow a level of automated directory to ISIS disk mapping and synthesis of error return codes. Other features include mapping tmp files so that multiple instances can be run at once. It is designed to run single applications with external windows/unix shells providing submit or make functionality. It makes no attempt to be cycle time accurate and as such it is fast." John Elliott's web page on Thames, a Unix based ISIS emulator from 2011, is at this link.

    Mark Ogden also referenced ZEMU by Joe Moore which apparently only resides on the Web site. Emulation includes the Intellec and MDS-800, among other 8080 Z80 ancient systems. It's supported as a 32-bit windows application.

    Decades ago, in the CP/MUG and SIG/M archives, is a set of codes to patch a version of ISIS-II V4.0 to run on a particular CP/M hardware system. In the SIG/M archives it's under "volume 40". The code and documentation give details. One convenient SIG/M archive is on the site. I suggested to Mark Ogden these patches may be interesting to compare to his deconstructed sources. He said, "With the decompiled source of isis 4.0 available it might be just as simple to modify this rather than create the hand patched versions of isis.t0 and isis.bin required for this simulator.[Also,] Version 4.3w provides support for a Winchester disk and as such might be a better starting point to support hard disks. OSIRIS even supports SASI, although there are a lot of other changes under the hood and it uses overlay code dependent on hardware configuration."

    Paul Birkel found "bloovis" codes, as I did years ago. bloovis apparently wrote an ISIS simulator "in the early '80's" for ISIS-II under MS-DOS/Turbo C.

    On the "unofficial CP/M archive site", under LANGUAGES; PL/M 80; there's a "PLM compiler : 343K ***UPDATED 05/25/98*** Here is the PLM compiler v. 4.0, along with an ISIS emulator". The ZIP file is at this link. It contains two self ZIP extracting EXE's ASM80.EXE and PLM80.EXE. Inside those EXEs (use 7-zip to extract them) are Intel's ISIS emulator V1.0. for MS-DOS and PL/M and ASM binary tools for the 8080. There's "another PL/M compiler" there, see notes below for details. Also note as above, that Intel's PL/M tools in binary and recovered PL/M are available from Mark Ogden's work.

    Martyn Vale tells me, "Thereís a full emulation of an MDS II implemented in Mame, however itís not exactly what you might call fast!" He suggests he's working on it as of 2021.

    John Elliott posted in on Jan 2011: I've now written an emulator [Thames] which emulates enough of ISIS to run [PL/M ISIS] tools under Unix. I've also made an updated with Unix-y build scripts rather than DOS batch files, which may find its way to in due time." - John Elliott. (John's work was extended by others, look around this Web page.)

    Intel's ISIS emulator, disassembled

    Paul Birkel wrote to me, there's a "ISX - An ISIS-II emulator" on Sourceforge. The page suggests the person found in the "unofficial CP/M Web site", an ISIS-II emulator, and then disassembled it. They do not identify what they found; here's some omitted omitted history of the executable. I suggest you save a copy of the sourceforge index page for its use-documentation. - Herb and and are in files of "P112 software" by "hperaza" Luis Hector Peraza Gonzalez, from year 2007. There's no documentation on the archive proper, past the index.html Web page.

    Looking at the sourceforge documents in, a source is titled "Digital Research's ISIS emulator ISX.COM". Other files also show "Digital Research". So it's a CP/M 80 (some version) means to overlay CP/M with support for ISIS II 8080 programs. Possibly the ISIS object/executable programs have to be "converted" and a CP/M EOF mark/byte established.

    As for the origins on the "unofficial CP/M archive" site, under LANGUAGES .. PL/M 80 .. there is quote "Another PLM Compiler : I am told that this is v. 3.1, an earlier version of the above compiler." end quote. Files there are and The 80X80 ZIP has a .COM file "IS14.COM" and "ISX.COM"; those may be the un-disassembled binaries referenced by Hector Peraza on sourceforge P112. They contain documentation and of course the Intel PL/M tools to be run under emulation.

    A README on the 80x80 says: quote"This ZIP file contains the ISIS-II PLM-80 v3.1 compiler. These files were pulled from the MPM2 source code disks and from the ISIS environment for MS-DOS provided by INTEL." The 80X86 ZIP has two files, a EXE and a README which starts quote: "The accompanying software is being provided by Intel Corporation in response to your request for this software."

    Further emulators and ISIS archives are discussed in the rest of this Web page.

    Links to other Web pages and resources

    Web pages on my Web site

    Check my Digital Research Web page for more discussion of PL/M and ISIS. Also my DRI version of this ISIS Web page.

    The OS/2 Museum Web site has an interest in the origins of MS-DOS, and therefore an interest in Intel's ISIS-II OS as an early MS-DOS development platform. Unfortunately, they have a truncated history of the early days of CP/M and MS-DOS and the IBM-PC which (as usual) suggests there was little value to the CP/M API (BIOS and BDOS calls). In fact, much early "MS-DOS" software was simply reassembled and translated CP/M software.

    In 2018 Mark Fisher pointed me to an article on their Web site about that history. "The IBM PC BIOS and Intel ISIS-II" by Michael Necasek is exerpted on this linked Web page, with links to useful resources such as C compilers, ISIS simulator, and a ISIS disk-image reader. Of course read the full article, link to the os2museum Web site is provided and good as of 2020.

    Here on my Web site we have some Intel and Multibus information, docs and boards. Also I have some Intel-related links in my Web page of S-100 and CP/M Web links. Parts of this document were moved from those pages in 2006-2007.

    At one time I had a substantial number of Intel ISIS diskettes. These were sold in 2006, and in 2010 the diskettes were "imaged" and put on a Web archive. In 2016, those imaged disks and other ISIS disks were "recovered" for their files. See notes below for specifics. Some discussion of that collection, and how the diskettes were imaged, is on this Web page about diskette recording methods. Another discussion about the collection itself, may be on this Web page of my site.

    I have a a Web page about my restoration of an Intel System 320 running Xenix.

    Another person, Bill Beech, found that page and discussed with mehis Intel and ISIS work in 2009 and following years. There are links to his site's resources on that page. Bill's ISIS tools and software may be spread on a number of his Web pages. I see some ISIS tools in his "Computers" section of his site under "Tools" and "8008/8080/8085 Tools". In 2015-16, Richard Main et al recovered those Intel diskettes as file and disk-image archives; his efforts aren't available in 2018, see more information below.

    Additional Web sites and discussion groups

    During years 2011 to present, I've made use of the "Intel Vintage" site by Mustafa A. Katie. Their accumuations of Intel manuals and software continue to grow. Here's their Intel software lists and links to actual software. Note that is an earlier, abandoned version of the site.

    In Oct 2016 Al Kossow called to my attention, the loss of a private Web page "". I investigated the Web Archive remains of the page for links to iRMX materials and groups. Here's a Web page that follows the trail left by It leads to an archive of a iRMX group called IRUG or International Real Time Users Group (Europe). There was a related Yahoo group of the same name; Yahoo removed their groups around 2016.

    In 2006-07, Udo Munk announced his updates to his Z80pack CP/M emulator for UNIX systems. This includes a number of collected CP/M OS sources, and also an MS-DOS version of an ISIS emulator to run the Intel PL/M native compiler. See my S-100 Web pointers page for more discussion of Udo Munk's work.

    ISIS has been discussed among the CP/M supporters of Usenet newsgroup comp.os.cpm. Here's the text of a 2009 discussion which helped to update this Web page.

    The Classic Cmp Web site in Oct 2006 has a page by Joe Rigdon from about 2000 to 2003 which describes one Intel MDS product and lists some manuals. Unfortunately it's hard to navigate this site to see the other MDS systems he describes; search his home page for "intel" to find other MDS sections.

    The Unofficial CP/M Web site has some PL/M compiler sources, written in Fortran. Look around the page and site for other sources and programs of Intel interest. For example the ISIS emulator at under the "PLM compiler" as "". Udo Munk's Z80PACK site likely has that also.

    There's also a note on comp.os.cpm for Jan 2011, referencing a Web page about original CP/M based ISIS emulator called ISX, on the "Sourceforge" source code site for the P112 computer. The Web page by "Hector Peraza?", describes the disassembled ISX emulator, and discussion about how to run it under CP/M 3.0 (?). The page was last updated in 2007. The P112 is a Z180 computer offered in the 1990's and again over a decade later.

    Matthiew Benoit has a page on the Intel iPDS 100 system which ran ISIS and PL/M. He has documents and files and links.

    The 2006 Wikipedia entry for PL/M has some interesting information and Web links. It will change of course over time.

    There is an article by Stan Mazor, co-creator of early Intel CPU's. "The History of the Microcomputer - Invention and Evolution", by Stanley Mazor, in the "PROCEEDINGS OF THE IEEE" VOL. 83, NO. 12, PP. 1600-1608, DECEMBER 1995. A copy of the article is here, with illustrations.

    Contact information:

    Herb Johnson
    New Jersey, USA
    To email @ me, see see my ordering Web page.

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