New blog post: Adventures in Archiving
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Jeff Parsons
Jeff Parsons
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_posts/2017-06-15-adventures-in-archiving.md
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---
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layout: post
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title: Adventures in Archiving
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date: 2017-06-15 22:00:00
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permalink: /blog/2017/06/15/
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machines:
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- type: pcx86
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id: ibm5150
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config: /devices/pcx86/machine/5150/cga/64kb/machine.xml
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autoMount:
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A:
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path: /disks/pcx86/dos/ibm/1.00/PCDOS100.json
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B:
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path: /apps/pcx86/1983/adventmath/ADVENTMATH100.json
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autoType: 8-10-81\\rb:\\ra:basica castle\\r
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---
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In October 1983, IBM released a game called "Adventures in Math", which apparently tried to make mathematics as
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exciting as walking through a dungeon full of locked doors, treasures, spiders, and more. I had never heard of this
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game, until I was recently browsing the [Internet Archive](https://archive.org/)'s
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[MS-DOS Showcase](https://archive.org/details/softwarelibrary_msdos_showcase):
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> This collection is a hand-picked set of selections from the MS-DOS Software Library of the Internet Archive.
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They've been chosen because they represent major parts of the MS-DOS story, because they are particularly impressive,
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and because they're fun. The intention is to eventually link these games to manuals and other materials as time goes on.
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> Curation was done by Jason Scott, Internet Archive's Software Librarian. He can be reached at jscott@archive.org with
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suggestion, questions and inquiries.
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For some reason, "Adventures in Math" caught my eye. You can play it on the
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[Internet Archive](https://archive.org/details/msdos_Adventures_in_Math_1983), or play it below, using PCjs. In
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fact, I invite you to play it in BOTH places, and let me know what you think.
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A word of warning: this is NOT a great game. I find it interesting only as an example of the challenges we face
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archiving and emulating old software.
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{% include machine.html id="ibm5150" %}
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Hosting the software on the PCjs website was more tedious than I'd expected, but that wasn't due to technical issues.
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The biggest challenge was isolating and recreating the original distribution software. You can find all the gory
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details on the page I created for "[Adventures in Math](/apps/pcx86/1983/adventmath/)".
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In short, although the software is archived inside multiple ZIP archives at the [Internet Archive](https://archive.org/),
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none of them appeared to contain an un-mingled, un-modified, distribution-only copy of the original software.
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And discovering that the software was archived inside multiple ZIP archives was a purely accidental discovery, not
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something one could easily determine using the Internet Archive's own search engine.
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### Emulation Challenges
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There are also some fundamental problems with the Internet Archive's approach to emulation. They load sets of files,
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along with custom batch files, into tightly coupled machine configurations, with no indication which files were part
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of the original software distribution, and no hardware details regarding their "mystery" machine configurations.
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And the Internet Archive's overall "emulation experience" is often not very faithful. Their rendering of
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"Adventures in Math" gives the impression that the game ran *much* faster than it actually ran on a 4.77Mhz IBM PC.
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While their emulator can be configured operate at different speeds, it's unclear which of their holdings have already
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been "tuned". As a fallback, they do provide some user controls:
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> "While the program is running, press CTRL-F11 to slow the program down. Pressing CTRL-F11 repeatedly will slow it
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down further, until the speed is more reasonable. (Pressing CTRL-F12 repeatedly will attempt to speed things up.)"
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but in general, the user has no idea what speed they have currently selected, or what the target speed should be.
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For users who simply want "to play the game," that may be fine, but an historian would probably prefer to see how the
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game originally operated and how each screen was painstakingly rendered, to better understand both the original user
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experience and the challenges that early software developers faced.
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The failure to archive software exactly as it was originally distributed, generally as one or more disk image (IMG)
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files along with scanned (PDF) copies of the documentation, is the most serious problem we collectively face. I don't
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blame the Internet Archive, because in most cases, they're simply archiving what someone else archived before them,
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and those earlier "archivists" often didn't take the time to thoroughly preserve and document everything.
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On the other hand, the Internet Archive could do a better job of cataloging its holdings, recording the provenance of
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everything they have archived, maintaining a clear separation of original material from subsequent modifications
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(including any modifications created solely for ease of emulation), providing more control over machine configurations,
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and enabling the use of third-party emulators -- like PCjs -- which may be able to perform a more faithful rendering
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of certain software packages.
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In addition, I would hope that anything the Internet Archive "archives" itself (ie, from original distribution media)
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is duplicated and preserved according to a *much* higher standard than any files, documents, etc, it has simply scraped
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from the Internet.
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*[@jeffpar](http://twitter.com/jeffpar)*
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*Jun 15, 2017*
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@ -194,47 +194,14 @@ which translates to:
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a:basica castle [run BASICA on drive A: and load CASTLE.BAS on drive B:]
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This is one of the preferred methods of demonstrating software in PCjs: loading unmodified disk images into machines
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that match the system requirements as closely as possible, powering the machine, and then automatically executing
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the same series of commands that an owner of that hardware and software combination might have executed.
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that match the software's system requirements as closely as possible, powering the machine, and then automatically
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executing a series of commands that an owner of that hardware and software combination would have likely executed.
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The other preferred method is to use a machine state file, which restores the machine to a state where the software is
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already running. This is the fastest approach, and it is useful when the software has an involved installation
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process, but it takes more effort to set up. The [VisiCalc (1981)](/apps/pcx86/1981/visicalc/) demo operates this way,
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but it does so purely for convenience (and because it predates the "autoType" feature).
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An alternative approach, adopted by the Internet Archive, involves modified disk images (eg, with custom batch files)
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loaded into tightly coupled machine configurations. While this approach offers ease of use, it's difficult for the
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user to download or inspect the software exactly as it was originally distributed, or to load the software into any
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machine configuration other than the "mystery" configuration chosen by the Internet Archive.
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Also, the Internet Archive's overall "emulation experience" is often not very faithful. Their rendering of "Adventures
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in Math" gives the impression that the game ran *much* faster than it actually ran on a 4.77Mhz IBM PC.
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While the Internet Archive's emulator can be configured operate at different speeds, it's unclear which of their
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holdings have already been "tuned". As a fallback, they do provide some user controls:
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> "While the program is running, press CTRL-F11 to slow the program down. Pressing CTRL-F11 repeatedly will slow it
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down further, until the speed is more reasonable. (Pressing CTRL-F12 repeatedly will attempt to speed things up.)"
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but in general, the user has no idea what speed they have currently selected, or what the target speed should be.
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For users who simply want "to play the game," that may be fine, but an historian would probably prefer to see how the
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game originally operated and how each screen was painstakingly rendered, to better understand both the original user
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experience and the challenges that early software developers faced.
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The failure to archive software exactly as it was originally distributed, generally as one or more disk image (IMG)
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files along with scanned (PDF) copies of the documentation, is the most serious problem we collectively face. I don't
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blame the Internet Archive, because in most cases, they're simply archiving what someone else archived before them,
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and those earlier "archivists" often didn't take the time to thoroughly preserve and document everything.
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On the other hand, the Internet Archive could do a better job of cataloging its holdings, recording the provenance of
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everything they have archived, maintaining a clear separation of original material from subsequent modifications (including
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any modifications created solely for ease of emulation), providing more control over machine configurations, and
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enabling the use of third-party emulators -- like PCjs -- that may be able to do a better job running and rendering
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some software packages.
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In addition, I would hope that anything the Internet Archive "archives" itself (ie, from original distribution media)
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is duplicated and preserved according to a *much* higher standard than any files, documents, etc, it has simply scraped
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from the Internet.
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References
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----------
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@ -7,12 +7,80 @@ permalink: /disks/pcx86/fixed/10mb/
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10Mb Hard Drive (Fixed Disk) Images
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---
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This folder contains the following 10Mb disk images:
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This folder contains the following 10Mb fixed disk images:
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* Empty formatted disk ([PCDOS200-EMPTY](PCDOS200-EMPTY.json))
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* PC-DOS 2.00 with Windows 1.01 for CGA ([PCDOS200-WIN101-CGA](pcdos200-win101-cga.xml))
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* PC-DOS 2.00 with Windows 1.01 for EGA ([PCDOS200-WIN101-EGA](pcdos200-win101-ega.xml))
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These disk images are used by various [Model 5160](/devices/pcx86/machine/5160/) machine configurations.
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These disk images are used by various IBM PC XT [Model 5160](/devices/pcx86/machine/5160/) machine configurations.
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NOTE: The empty disk is *completely* empty. It was partitioned with the PC-DOS 2.00 **FDISK** utility, allocating
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the entire disk to a single DOS partition, and then it was formatted with the PC-DOS 2.00 **FORMAT** utility.
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Neither the **FORMAT** "/S" option nor the **SYS** command were used, so no system files were transferred, leaving
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the disk completely empty and non-bootable.
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After formatting, PC-DOS 2.00 reports:
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10592256 bytes total disk space
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10592256 bytes available on disk
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As explained in the [DiskDump source code](/modules/diskdump/lib/diskdump.js), in its description of the 10Mb
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BPB, a 10Mb "Type 3" PC XT fixed disk contains:
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306 cylinders
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4 heads
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17 sectors/track
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for a total of 20808 sectors or 10,653,696 bytes. However, as p.1-179 of the PC XT Technical Reference Manual
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(April 1983) notes:
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WARNING: The last cylinder on the fixed disk drive is reserved for diagnostic use.
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Diagnostic write tests will destroy any data on this cylinder.
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And this is confirmed by the PC XT BIOS, p.A-94, in the code for the "GET PARAMETERS (AH = 8)" function:
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C800:03B2 268B07 MOV AX,ES:[BX] ; MAX NUMBER OF CYLINDERS
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C800:03B5 2D0200 SUB AX,2 ; ADJUST FOR 0-N AND RESERVE LAST TRACK
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By "RESERVE LAST TRACK", they really meant "RESERVE LAST CYLINDER", because 68 (not 17) sectors are reserved at
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the end of the disk. In addition, the first sector of the disk is reserved for the Master Boot Record (MBR), so there
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are a total of 69 reserved sectors. (20808 - 69) = 20739 or 0x5103, which is exactly what's stored in the "total
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sectors" field of the disk's BPB, yielding a total partition size of 10,618,368 bytes.
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However, that 69-sector overhead is not the end of the story. There is also overhead incurred by the FAT file system,
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which, in this case, consists of:
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- Boot sector (1)
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- FAT sectors (2 * 8 = 16)
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- Root directory sectors (32)
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for a total of 49 sectors, leaving (20739 - 49) = 20690 sectors. Moreover, free space is measured in clusters,
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not sectors, and the partition uses 8 sectors/cluster, leaving room for 2586.25 clusters. Since a fractional cluster
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is not allowed, another 2 sectors are lost, bringing the total FAT file system overhead to 51 sectors.
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Thus, actual free space is (20739 - 51) * 512, or 10,592,256 bytes, which is exactly what DOS reports as the available
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space.
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Some sources on the internet (eg, http://www.wikiwand.com/en/Timeline_of_DOS_operating_systems) claim that the (FAT)
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file system overhead for the XT's 10Mb disk is "50 sectors". As they explain:
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"The fixed disk has 10,618,880 bytes of raw space: 305 cylinders (the equivalent of tracks) × 2 platters
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× 2 sides or heads per platter × 17 sectors per track = 20,740 sectors × 512 bytes per sector = 10,618,880
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bytes...."
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and:
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"With DOS the only partition, the combined overhead is 50 sectors leaving 10,592,256 bytes for user data:
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DOS's FAT is eight sectors (16 sectors for two copies) + 32 sectors for the root directory, room for 512
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directory entries + 2 sectors (one master and one DOS boot sector) = 50 sectors...."
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However, that's incorrect. First, the disk has 306 cylinders, not 305. Second, there are TWO overhead values:
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the overhead OUTSIDE the partition (69 sectors) and the overhead INSIDE the partition (51 sectors). They failed
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to account for the reserved cylinder in the first calculation and the lost fractional cluster in the second
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calculation, and then they conflated the two values to produce a single (incorrect) result.
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---
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To use one of these disks with another machine configuration, include:
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@ -905,8 +905,8 @@ class Debugger extends Component
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* And to avoid conflicts with MACRO-10 syntax, I've replaced the original mod operator ('%') with '^/'.
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*
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* The MACRO-10 binary shifting suffix ('B') is a bit more problematic, since a capital B can also appear
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* inside symbols. So I pre-scan for that suffix and replace all non-symbolic occurrences with an internal
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* shift operator ('^_').
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* inside symbols, or inside hex values. So if the default base is NOT 16, then I pre-scan for that suffix
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* and replace all non-symbolic occurrences with an internal shift operator ('^_').
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*
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* Note that Str.parseInt(), which parseValue() relies on, supports both the MACRO-10 base prefix overrides
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* and the binary shifting suffix ('B'), but since that suffix can also be a bracketed expression, we have to
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@ -923,7 +923,9 @@ class Debugger extends Component
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* that to generate an error; if we converted it to "AB", evaluation might inadvertently succeed.
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*/
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var regExp = /({|}|\|\||&&|\||\^!|\^B|\^O|\^D|\^L|\^-|~|\^_|_|&|!=|!|==|>=|>>>|>>|>|<=|<<|<|-|\+|\^\/|\/|\*|,,| )/;
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sExp = sExp.replace(/(^|[^A-Z0-9$%.])([0-9]+)B/, "$1$2^_").replace(/\s+/g, ' ');
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if (this.nBase != 16) {
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sExp = sExp.replace(/(^|[^A-Z0-9$%.])([0-9]+)B/, "$1$2^_").replace(/\s+/g, ' ');
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}
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var asValues = sExp.split(regExp);
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value = this.parseArray(asValues, 0, asValues.length, this.nBase, aUndefined);
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if (value !== undefined && fPrint) {
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