rburns@teknowledge-vaxc.ARPA (Mr. Doom and Gloom) (12/30/87)
I have two questions about CD-ROM 1) Is it possible to write to both sides of a CD? If some wished to create a double sided CD which the user would switch like a phonograph record, would this be feasible? 2) Has anyone announced development of a WORM media which is compatible with CD-ROM readers? I have the feeling there really isn't anything highly practical yet for small volume CD production. I know I would find such a system HIGHLY attractive, even if it lacked some of the performance of existing WORM media. Thanks. Randy Burns
daford@watdragon.waterloo.edu (Daniel Ford) (01/03/88)
In article <19898@teknowledge-vaxc.ARPA> rburns@teknowledge-vaxc.ARPA (Mr. Doom and Gloom) writes: >1) Is it possible to write to both sides of a CD? If some wished to >create a double sided CD which the user would switch like a phonograph >record, would this be feasible? As I understand it, CD ROM discs in their current form could not be double sided. I don't have my reference books with me a the moment, but I believe the thickness and refractive index of the plastic covering the pits is crucial to the accurate focusing of the laser or lasers (some drives have more than one) on to the track. Basically, if this is true, would need a disc twice as thick. Another simple problem with two sided discs is labeling. Where would you put the name of the disc? LP's get around this problem by being large, not really a solution here.... >2) Has anyone announced development of a WORM media which is compatible >with CD-ROM readers? I have the feeling there really isn't anything >highly practical yet for small volume CD production. I know I would find >such a system HIGHLY attractive, even if it lacked some of the >performance of existing WORM media. I believe that it may be possible to construct a drive that would read both CD ROM and WORM discs but there are some problems. The big one is the different recording formats used in the two types of disks. CD ROM is CLV (constant linear velocity) and WORM is CAV (constant angular velocity). A CD ROM drive varies the speed of rotation of the disc while a WORM drive does not. It would be tricky but not impossible, maybe somebody out there knows more about such a beast... Dan Ford -- --------------------------------------------------------------------- Daniel A. Ford daford@watdragon.uucp CS Department daford%watdragon@waterloo.csnet U. of Waterloo daford%watdragon%waterloo.csnet@csnet-relay.arpa
yba@athena.mit.edu (Mark H Levine) (01/04/88)
In article <4469@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: >As I understand it, CD ROM discs in their current form could not be >double sided. > >Another simple problem with two sided discs is labeling. Where would >you put the name of the disc? LP's get around this problem by being large, >not really a solution here.... > >I believe that it may be possible to construct a drive that would read >both CD ROM and WORM discs but there are some problems. The big one is >the different recording formats used in the two types of disks. > This seems unnecessarily pessimistic on several counts: Music CDs which use the same basic technology + a D/A converter come double sided, CD-ROM drives can mechanically accomodate these disks as far as I have seen (they use the same bloody drive in the case of Hitachi product I was shown, and the only restriction on WORM product was the form factors involved). The labelling problem is somewaht silly -- two-sided music cds have labels on both sides, as do 8, 10, and 12 inch optical disks for video (with 2 sides). The lasers do not seem to have any trouble with the plastic coat, nor would I expect any. I expect you will see read/write media just about the time compatible WORM drives would be ready, so the entire problem there may be moot. This is of course only my opinion, which I do not represent as authoratative. I work on integration of video with our X Window System here at MIT, along with the Video Courseware Group which is developing interactive teaching material. We have video workstations which can put video inside a window, have attached CATV and 12 inch video disk players, and are producing our own disks. So far we have only experimented briefly with the CD format, and are looking to CDI and DVI as areas to explore in the future. I would be interested in hearing experience others may already have had with these.
daford@watdragon.waterloo.edu (Daniel Ford) (01/05/88)
In article <2132@bloom-beacon.MIT.EDU> yba@athena.mit.edu (Mark H Levine) writes: >In article <4469@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: >>As I understand it, CD ROM discs in their current form could not be >>double sided. >This seems unnecessarily pessimistic on several counts: > >Music CDs which use the same basic technology + a D/A converter come double >sided, CD-ROM drives can mechanically accomodate these disks as far as I have >seen (they use the same bloody drive in the case of Hitachi product I was >shown, and the only restriction on WORM product was the form factors involved). >The labelling problem is somewaht silly -- two-sided music cds have labels on >both sides, as do 8, 10, and 12 inch optical disks for video (with 2 sides). >The lasers do not seem to have any trouble with the plastic coat, nor would >I expect any. I may be displaying my ignorance, but as far as I know music CD's do NOT come double sided. They may look double sided because one can see the silver through the transparent top side, but they are not. Also, I don't see how one could expect a laser to penetrate an optically opaque label and read the data stored on the disk surface below. This seems doubly strange since the manual for the above mentioned Hitachi drive warns that if the disk surface is fogged by condenstation the drive is likely to have problems reading data. Dan Ford -- --------------------------------------------------------------------- Daniel A. Ford daford@watdragon.uucp CS Department daford%watdragon@waterloo.csnet U. of Waterloo daford%watdragon%waterloo.csnet@csnet-relay.arpa
david@ms.uky.edu (David Herron -- Resident E-mail Hack) (01/07/88)
Music CD's do indeed use the same formats as Data CD's.
Music CD's are single sided whereas Data CD's can be double sided.
Music CD's are single sided to allow for labelling on one side. I would
have liked for them to be double sided. There is ample room for some
labelling in the dead area's of the disk -- that is, I assume I'm interpreting
what I see properly. On a Music CD there's a band of "smooth-continuous"
looking "silver" around the outside, inside that there's a band of not
so "smooth-continuous" looking "silver", inside that there's another band
of "smoth" stuff. I assume that the data is in the not-so-smooth parts
and the smooth parts don't hold any data and can be used for labelling.
2 1/2 hrs of music on a disk would be nice. But then that assumes that
the record companies can think of ways to distribute that much music in
one package. From past experience I don't think they could. They haven't
been able to get beyond thinking in terms of the "Album" format.
I was looking through BYTE last night and saw someone advertising CD ROM
readers and WORM drives. The ROM readers had attachments available which
would allow one to play Music CD's in the ROM reader.
I had a thought. Do WORM drives use the same data formats? If not, can they?
I had this silly thought about making backup copies of my Music CD's :-).
--
<---- David Herron -- The E-Mail guy <david@ms.uky.edu>
<---- or: {rutgers,uunet,cbosgd}!ukma!david, david@UKMA.BITNET
<----
<---- Winter health warning: Remember, don't eat the yellow snow!lawrence@bbn.COM (Gabe Lawrence) (01/07/88)
yba@athena.mit.edu (Mark H Levine) writes: > >This seems unnecessarily pessimistic on several counts: > >Music CDs which use the same basic technology + a D/A converter come double >sided, CD-ROM drives can mechanically accomodate these disks as far as I have Funny... I own a couple of hundred music CDs and not one of them is double-sided. >seen (they use the same bloody drive in the case of Hitachi product I was >shown, and the only restriction on WORM product was the form factors involved). >The labelling problem is somewaht silly -- two-sided music cds have labels on >both sides, as do 8, 10, and 12 inch optical disks for video (with 2 sides). >The lasers do not seem to have any trouble with the plastic coat, nor would >I expect any. >... Sorry, I've never seen a music CD, or video disc for that matter although I'm not as sure, that was labelled on both sides. The lasers might be able to read through surface dust or fingerprints but through completely opaque enamal labelling paints?? C'mon, let's be realistic!! Call me "Pessimistic in Cambridge", =Gabriel Lawrence= USENET: ...!harvard!bbn!ccv!lawrence INTERNET: lawrence@BBN.COM
daford@watdragon.waterloo.edu (Daniel Ford) (01/08/88)
In article <7990@e.ms.uky.edu> david@ms.uky.edu (David Herron -- Resident E-mail Hack) writes: >Music CD's do indeed use the same formats as Data CD's. > >Music CD's are single sided whereas Data CD's can be double sided. > >what I see properly. On a Music CD there's a band of "smooth-continuous" >looking "silver" around the outside, inside that there's a band of not >so "smooth-continuous" looking "silver", inside that there's another band >of "smoth" stuff. I assume that the data is in the not-so-smooth parts >and the smooth parts don't hold any data and can be used for labelling. The inner band of "smooth-continuous" silver has no data and is called the "lead in". The outer "smooth-continous" area also has no data and is called the "lead out". No labeling should go on these areas. The lead in starts from the centre to allow for playing different sized disks on the same drive. I believe that there is now a CD single that is a bit smaller than the regular disc and holds about 15 to 20 minuties of music. >I had a thought. Do WORM drives use the same data formats? If not, can they? >I had this silly thought about making backup copies of my Music CD's :-). The two types of discs use different recording formats. WORM drives use a CAV scheme just like magnetic disks and CD ROM uses CLV which is basically one long spiral track. You could make a "backup" but the discs are so tough I wouldn't worry about it. In Japan they are marketing a hybrid disk that uses CD for sound and optical disk for video. These little babies are used to sell music video singles. Apparently it is a hot item. Dan Ford -- --------------------------------------------------------------------- Daniel A. Ford daford@watdragon.uucp CS Department daford%watdragon@waterloo.csnet U. of Waterloo daford%watdragon%waterloo.csnet@csnet-relay.arpa
mark@cygnet.CYGNETSYSTEMS (Mark Quattrocchi) (01/15/88)
In article <4469@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: >In article <19898@teknowledge-vaxc.ARPA> rburns@teknowledge-vaxc.ARPA (Mr. Doom and Gloom) writes: >>1) Is it possible to write to both sides of a CD? If some wished to >>create a double sided CD which the user would switch like a phonograph >>record, would this be feasible? > >As I understand it, CD ROM discs in their current form could not be >double sided. I don't have my reference books with me a the moment, >but I believe the thickness and refractive index of the plastic >covering the pits is crucial to the accurate focusing of the laser or >lasers (some drives have more than one) on to the track. Basically, >if this is true, would need a disc twice as thick. > >Another simple problem with two sided discs is labeling. Where would >you put the name of the disc? LP's get around this problem by being large, >not really a solution here.... > >>2) Has anyone announced development of a WORM media which is compatible >>with CD-ROM readers? I have the feeling there really isn't anything >>highly practical yet for small volume CD production. I know I would find >>such a system HIGHLY attractive, even if it lacked some of the >>performance of existing WORM media. > >I believe that it may be possible to construct a drive that would read >both CD ROM and WORM discs but there are some problems. The big one is >the different recording formats used in the two types of disks. >CD ROM is CLV (constant linear velocity) and WORM is CAV (constant angular >velocity). A CD ROM drive varies the speed of rotation of the disc >while a WORM drive does not. It would be tricky but not impossible, >maybe somebody out there knows more about such a beast... Not true. All of the 5 1/4" worm drives are currently using the CLV format in order to increase the density up to about 600 meg per disc (double sided). The 12" market is also working on the CLV format which would give them a total capacity of about 4 gigabytes per platter.
mark@cygnet.CYGNETSYSTEMS (Mark Quattrocchi) (01/15/88)
In article <4481@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: > >In article <2132@bloom-beacon.MIT.EDU> yba@athena.mit.edu (Mark H Levine) writes: >>In article <4469@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: >>>As I understand it, CD ROM discs in their current form could not be >>>double sided. >>This seems unnecessarily pessimistic on several counts: >> >>Music CDs which use the same basic technology + a D/A converter come double >>sided, CD-ROM drives can mechanically accomodate these disks as far as I have >>seen (they use the same bloody drive in the case of Hitachi product I was >>shown, and the only restriction on WORM product was the form factors involved). >>The labelling problem is somewaht silly -- two-sided music cds have labels on >>both sides, as do 8, 10, and 12 inch optical disks for video (with 2 sides). >>The lasers do not seem to have any trouble with the plastic coat, nor would >>I expect any. > > > > >I may be displaying my ignorance, but as far as I know music CD's do NOT >come double sided. They may look double sided because one can see the >silver through the transparent top side, but they are not. Also, I don't see >how one could expect a laser to penetrate an optically opaque label and read >the data stored on the disk surface below. This seems doubly strange since >the manual for the above mentioned Hitachi drive warns that if the >disk surface is fogged by condenstation the drive is likely to have problems >reading data. Absolutely correct! Givem hell Harry.
mark@cygnet.CYGNETSYSTEMS (Mark Quattrocchi) (01/15/88)
In article <5826@ccv.bbn.COM> lawrence@BBN.COM (Gabe Lawrence) writes: >yba@athena.mit.edu (Mark H Levine) writes: >> >>This seems unnecessarily pessimistic on several counts: >> >>Music CDs which use the same basic technology + a D/A converter come double >>sided, CD-ROM drives can mechanically accomodate these disks as far as I have > >Funny... I own a couple of hundred music CDs and not one of them is >double-sided. > >>seen (they use the same bloody drive in the case of Hitachi product I was >>shown, and the only restriction on WORM product was the form factors involved). >>The labelling problem is somewaht silly -- two-sided music cds have labels on >>both sides, as do 8, 10, and 12 inch optical disks for video (with 2 sides). >>The lasers do not seem to have any trouble with the plastic coat, nor would >>I expect any. >>... > >Sorry, I've never seen a music CD, or video disc for that matter although >I'm not as sure, that was labelled on both sides. The lasers might >be able to read through surface dust or fingerprints but through completely >opaque enamal labelling paints?? C'mon, let's be realistic!! > >Call me "Pessimistic in Cambridge", > =Gabriel Lawrence= Laser discs do have labels on both sides and they are in the middle just like a record.
mark@cygnet.CYGNETSYSTEMS (Mark Quattrocchi) (01/15/88)
In article <4515@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes: >In article <7990@e.ms.uky.edu> david@ms.uky.edu (David Herron -- Resident E-mail Hack) writes: >>Music CD's do indeed use the same formats as Data CD's. >> >>Music CD's are single sided whereas Data CD's can be double sided. >> >>what I see properly. On a Music CD there's a band of "smooth-continuous" >>looking "silver" around the outside, inside that there's a band of not >>so "smooth-continuous" looking "silver", inside that there's another band >>of "smoth" stuff. I assume that the data is in the not-so-smooth parts >>and the smooth parts don't hold any data and can be used for labelling. > >The inner band of "smooth-continuous" silver has no data and is called >the "lead in". The outer "smooth-continous" area also has no data and is called >the "lead out". No labeling should go on these areas. > >The lead in starts from the centre to allow for playing different sized disks >on the same drive. I believe that there is now a CD single that is a bit >smaller than the regular disc and holds about 15 to 20 minuties of music. > >>I had a thought. Do WORM drives use the same data formats? If not, can they? >>I had this silly thought about making backup copies of my Music CD's :-). > >The two types of discs use different recording formats. WORM drives use >a CAV scheme just like magnetic disks and CD ROM uses CLV which is basically >one long spiral track. You could make a "backup" but the discs are so >tough I wouldn't worry about it. > >In Japan they are marketing a hybrid disk that uses CD for sound and >optical disk for video. These little babies are used to sell music video >singles. Apparently it is a hot item. > Dan Ford > This is called the CDV format as was first introduced as 8" discs.