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cyhist Apr. 9 1998 A
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========================================================================= Date: Thu, 9 Apr 1998 10:56:35 -0400
Reply-To: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> Sender: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> From: "christopher f. chiesa" <cfchiesa@SERVTECH.COM>
Subject: Re: CYHIST Digest - 7 Apr 1998 to 8 Apr 1998 (#1998-14)
In-Reply-To: <199804090443.AAA15831@servtech.com> from Automatic digest
processor at "Apr 9, 98 00:36:49 am"
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______________________________________________________________________
Community Memory: Discussion List on the History of Cyberspace ______________________________________________________________________
Fred Cisin <fcisin@MERRITT.EDU> wrote:
>Disk format conversion remains an important issue, as there were over 2500 different mutually incompatible microcomputer floppy disk formats! Any that are soft-sectored, double density are at least theoretically readable by the PC hardware.
It seems clear to me that the major bottleneck in archival of old media, and migration of old data to newer media, is specifically the translation of information from the physical to the digital realm. Clearly, once a set of custom-hardware-specific data has been brought into the digital realm we can do "anything we want" with it, and most of the technical difficulties essentially disappear (at least from MY point of view; I'm a programmer and I consider software "the easy part!"). It seems to me, therefore, that the lower the level at which we can transfer physical information to digital, the less drastic our labors need be in the area of preserving, refurbishing, and/or reinventing those 2500 different-and- incompatible custom, PHYSICAL mechanisms. I say, virtualize as much of the job as possible -- and here's how I'd approach it:
Judging from the content of this mailinglist, it appears that the specific technical details of many, if not most, if not ALL, of those 2500 mechanisms are fairly well known: the algorithms by which bits are encoded into magnetic-polarity transitions, the width, spacing, and overall "shape" of the magnetic "tracks" of interest, the identification of "blocks" or "sectors" within each track, the management of a diskful of blocks as a "filesystem" perhaps, and so on and so forth. These things are, if not standard, certainly "fundamental" to some degree, to the point where I expect that the algorithms by which they are performed are probably fairly "well known."
Assuming this to be the case, why not build a generic magnetic-media surface-mapper capable of delivering a complete map of the magnetic polarities across the entire surface of an arbitrary magnetic disk? Initially, pass a "SQUID" across the surface of the media and record the magnetic field variations it detects. Use image-processing tech- niques on the resulting "map" dataset to isolate the expected/known positions of data tracks for the type of media you're working with (whereupon you can probably THROW AWAY the rest of the map data). Trace the magnetic variations "along" each track, and run the appro- priate (FM, MFM, etc.) decoding algorithm over them to extract a bit- stream. Use similar methods, along with either known specifications or inspection-based reverse-engineering, to reconstruct the byte- stream comprising the track data, extract the "raw disk blocks," in- terpret these as a filesystem, etc. etc., up to whatever level of abstraction you desire.
As I said, in THEORY, at least, it seems almost EASY.
Comments?
Chris Chiesa
cfchiesa@servtech.com
______________________________________________________________________
Reply-To: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> Sender: "CYHIST Community Memory: Discussion list on the History of
Cyberspace" <CYHIST@MAELSTROM.STJOHNS.EDU> From: "christopher f. chiesa" <cfchiesa@SERVTECH.COM>
Subject: Re: CYHIST Digest - 7 Apr 1998 to 8 Apr 1998 (#1998-14)
In-Reply-To: <199804090443.AAA15831@servtech.com> from Automatic digest
processor at "Apr 9, 98 00:36:49 am"
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit
______________________________________________________________________
Community Memory: Discussion List on the History of Cyberspace ______________________________________________________________________
Fred Cisin <fcisin@MERRITT.EDU> wrote:
>Disk format conversion remains an important issue, as there were over 2500 different mutually incompatible microcomputer floppy disk formats! Any that are soft-sectored, double density are at least theoretically readable by the PC hardware.
It seems clear to me that the major bottleneck in archival of old media, and migration of old data to newer media, is specifically the translation of information from the physical to the digital realm. Clearly, once a set of custom-hardware-specific data has been brought into the digital realm we can do "anything we want" with it, and most of the technical difficulties essentially disappear (at least from MY point of view; I'm a programmer and I consider software "the easy part!"). It seems to me, therefore, that the lower the level at which we can transfer physical information to digital, the less drastic our labors need be in the area of preserving, refurbishing, and/or reinventing those 2500 different-and- incompatible custom, PHYSICAL mechanisms. I say, virtualize as much of the job as possible -- and here's how I'd approach it:
Judging from the content of this mailinglist, it appears that the specific technical details of many, if not most, if not ALL, of those 2500 mechanisms are fairly well known: the algorithms by which bits are encoded into magnetic-polarity transitions, the width, spacing, and overall "shape" of the magnetic "tracks" of interest, the identification of "blocks" or "sectors" within each track, the management of a diskful of blocks as a "filesystem" perhaps, and so on and so forth. These things are, if not standard, certainly "fundamental" to some degree, to the point where I expect that the algorithms by which they are performed are probably fairly "well known."
Assuming this to be the case, why not build a generic magnetic-media surface-mapper capable of delivering a complete map of the magnetic polarities across the entire surface of an arbitrary magnetic disk? Initially, pass a "SQUID" across the surface of the media and record the magnetic field variations it detects. Use image-processing tech- niques on the resulting "map" dataset to isolate the expected/known positions of data tracks for the type of media you're working with (whereupon you can probably THROW AWAY the rest of the map data). Trace the magnetic variations "along" each track, and run the appro- priate (FM, MFM, etc.) decoding algorithm over them to extract a bit- stream. Use similar methods, along with either known specifications or inspection-based reverse-engineering, to reconstruct the byte- stream comprising the track data, extract the "raw disk blocks," in- terpret these as a filesystem, etc. etc., up to whatever level of abstraction you desire.
As I said, in THEORY, at least, it seems almost EASY.
Comments?
Chris Chiesa
cfchiesa@servtech.com
______________________________________________________________________
