Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ames!decwrl!uunet!mcsun!ukc!dcl-cs!aber-cs!odin!pcg From: pcg@cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.arch Subject: Re: moving laser beams, not media Message-ID: Date: 3 Aug 90 12:50:41 GMT References: <2635@mindlink.UUCP> <10048@pt.cs.cmu.edu> <40535@mips.mips.COM> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 92 In-reply-to: cprice@mips.COM's message of 31 Jul 90 21:10:38 GMT "cprice" == Charlie Price ??? writes: cprice> In article <10048@pt.cs.cmu.edu> cprice> lindsay@MATHOM.GANDALF.CS.CMU.EDU (Donald Lindsay) writes: lindsay> Beats me. However, I would certainly hope that the access mechanism lindsay> involves fewer moving parts than it does now. lindsay> Specifically, it would be nice if we scanned a laser beam over the lindsay> media, rather than rotated the media. cprice> Don't CDs at least, pretty much *depend* on the read beam being cprice> delivered orthogonally to the media since the effect used cprice> to sense bits is interference in reflected light, not the cprice> amount of light reflected? Here you have the possibility of using a cup-shaped medium (or cylinder shaped, if you use a light source array instead of a point). There is no reason to restrict oneself to flat recording media, as you later observe musign about recording spheres. cprice> A second problem is knowing whether you are really looking at cprice> the information that you think you are. A disk has a lot of cprice> "servo" data that lets you position to read and lets you know cprice> that you are in the right place. [ ... and heavvy heads cprice> providing hysteresis in positioning ... ] You would use television like scanning, like CRT memories of the fifties. Precision positioning can be done, and then you can inscribe the medium with servo information within each scan line, to keep the scanning beam in synch. Or you could instead random position the beam, by using a less precise homing beam onto larger features of the surface, and then the read/write beam. cprice> A system that depends on mass is immune to some level of vibration cprice> because you don't move the masses quickly enough that you cprice> can't compensate for them. But we are using granite cabinets here, of course. Thermal problems can get us pretty badly, not just vibration. We also would like to use phase conjugated mirrors as well, for the same reasons. I have little doubt (let's be optimistic) that the technology exists, if only because it has been developed for telescopes, and optical and electronic microscopes, not to mention chip litographers of various types. cprice> You have to LOOK at the reflected light, right? Why ever? You can just use as recording surface something wih holes in it, and put under it a photoconductive surface. Remember that we could be scanning the recording surface strictly sequentially, so looking at only one bit at a time, of known coordinates. cprice> You need some way to either compensate for or render unimportant cprice> defects in the media (nothing is perfectly flat, perfectly smooth, cprice> identically transparent, ...). This was a problem also with CRT memories (carbon dust from the coils falling on the phospor, and thus literally blacking out a bit), and that is why they (Manchester University) started working with ECC like ideas. In case this is not already obvious, I have been thinking about a granite pyramid a few feet tall with a cup shaped recording medium in its base and a laser eye at its top. :-) :-) This would have no moving parts at all (if Fabry-Perot devices are used to do the modulation and deflection), nanosecond access times and terabit capacities (if we can find a recording medium that is good enough), write once properties, and a fairly steep price. One would use a very fast photoconductive/sensitive recording medium in which you burn holes to write; when you read, if the laser goes thru the hole and the surface is not illuminated, if there is no hole, the laser hits and illuminates the surface. The surface would be black and very thin to avoid requiring a large increase in the laser power to write thru, and writing would be done with a slightly wider beam than for reading. There could be endless variations; the surface could just be "black paint", and the photoconductor/sensing surface coated beneath it, or a transparent surface that blisters becoming opaque when burned, etc... The surface could become diffractive, or shorter/taller by a wawelength, getting beam cancellation, or whatever. There are loads of optical effects. Does anybody know what could be used? Do we have any hope? -- Piercarlo "Peter" Grandi | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcsun!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk