-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Content-ID:
Hola :)
On Tuesday 29 December 2009 22:14:39 Carlos E. R. wrote:
Respecto a la diferencia entre - y + R, tengo por ahí un enlace que lo explica. No es sutil,, es transcendental. Lo tengo en el otro ordenador, no puedo empastarlo aquí.
Una vez me leí las diferencias, pero no me acuerdo, si lo puedes pegar, se agradece (es por no buscarlo yo, estoy en modo vago 0;)
http://www.digitalfaq.com/reviews/dvd-media.htm Reviews > Blank DVD Media Quality De ahí saco la calidad de cada modelo de dvd, independientemente del fabricante. Los DVD tienen un código (que se puede leer con dvd+rw-mediainfo), por el que mediante tablas, puedes saber quien realmente lo ha fabricado. Puede ser un disco de marca de renombre y estar fabricado en un sitio del montón de otro pais. Hay pocos clasificados como "de primera calidad". http://adterrasperaspera.com/blog/2006/10/30/how-to-choose-cddvd-archival-me... Lo empasto: Why DVD+R? - ---------- This is the most technical section of the article. If you don’t understand the basics of how CD/DVD media works, or find such technical discussions boring, skip to the next section. As I said earlier, DVD-R sucks for data preservation for three reasons: inferior error correction, inferior ‘wobble’ tracking, and the fact its data writing methods look like an un-needed halfway point between CD-R and DVD+R. The wobble tracking I shall explain first, then the error corrections method, then the specifics of ATIP/pre-pit/ADIP optimum power settings. For a CD/DVD burner to track where it is on the disc, it uses three things: the ‘wobble’ of the data track (where it actually wobbles back and forth instead of in a straight line) to tell where it is in the track, the position of the track to tell where it is on the disc, and some additional information on the disc to tell where the track (singular, as CDs and DVDs only have one track, and it is written in a concentric spiral) begins and ends. This additional information on a CD-R is called the ATIP (Absolute Time In Pregroove), which contains how long the track is, where it begins, what the maximum and minimum writing speeds are, what formula dye it uses, who actually made it, optimum power control settings, and error correction data. The ATIP is stored as a frequency modulation in the wobble itself. However, since the wobble changes subtly to encode data, it is impossible to use with the small size of tracks DVD requires, as electric noise in the laser pickup and wobbles introduced by the electric motor spinning the disc, these could easily be read as frequency changes in the real track itself. On DVD-R, they tried to solve the problem with something called ‘pre-pits’ where spikes in the amplitude of the wobble appear due to pits fully out of phase with the rest of the track (ie, between two spirals of the track, where there is no data). This can be viewed as a simple improvement over CD-R as it makes it easier to track the wobble (since the wobble is constant except for the easy to detect and remove spikes). Unfortunately, this method as one flaw: due to electric noise in the laser pickup, it would be very easy to miss the pre-pit (or read one that wasn’t actually there) if the disc were damaged or spun at fast speeds. The time to read a pre-pit is 1T (roughly .0000000038th of a second), which even for a computer can be easy to miss. DVD-R traded hard to track frequency changes for hard to read wobble-encoded data. On a DVD+R, however, they came up with a much better method. Instead of changing the frequency of the wobble, or causing amplitude spikes in the wobble, they use complete phase changes. Where CD-R’s and DVD-R’s methods make you choose between either easy wobble tracking or easy ATIP reading, DVD+R’s method makes it very easy to track the wobble, and also very easy to encode data into the wobble. DVD+R’s method is called ADIP (ADdress In Pre-groove), which uses a phase change method. With ADIPs’ phase changes, the direction of the wobble changes and continues on going in the exact opposite direction (ie, counter-clockwise to clockwise, or the reverse). For example, if the wobble was ‘going up’, the phase change causes it to instantly reverse direction start ‘going down’ no matter where it in the wobble cycle. The phase change is very easy to detect, and also continues for a set period (in this case, one 32T section of the track, or 32 times longer than the pre-pit method of DVD-R). The state of the phase change (clockwise or counter-clockwise) encodes the individual bits in each block In essence, with the phase change method, not only do you have an easy way of tracking the wobble, but you now have an easy way of reading wobble-encoded data. As I mentioned earlier, this wobble-encoded data includes error correction of wobble-encoded data itself. Error correction is the most important part of media, because if it does not work, then you’ve lost your data, even if there is nothing seriously wrong with the disc. The DVD-R specification states that for every 192 bits, 64 of them are not protected under any scheme, 24 of them are protected by 24 bits of parity, and the last 56 bits are protected by another 24 bits of parity. This weird (to put it mildly) scheme allows you to easily scramble or lose 25% of the data that is required to read your disk! This information is almost more important than the actual data burned on the disc itself. The DVD+R specification, however, states that for every 204 bits of information, it is split into four blocks of 52 bits containing 1 sync bit to prevent misreading because of phase changes, 31 bits of data, and a 20 bit parity (that protects all 32 bits of data). The sync bit is always the same value in all four blocks, and exists only to prevent phase inversions. Now, the third item on the list: how DVD+R discs burn better. As I said earlier, ATIP/pre-pit/ADIP stores information about optimum power control settings. This information is basically formulas stating how much output power is needed, what the laser startup power should be, and other pieces of information you require to properly burn a DVD. Optimum power control output is dependent on three things: burning speed, laser wavelength, and information given to the drive about the media. DVD-R basically fails on all three accounts because DVD+R simply includes far more information about the media in the ADIP data than DVD-R does in it’s pre-pit data. DVD+R includes four optimum profiles, one for four major burning speeds (usually 2x, 4x, 6x, and 8x, though this can change as speeds increase). Each of these profiles include optimum power output based on laser wavelength, more precise laser power settings, and other additional information. With this information, any DVD+R burner can far more optimize it’s burning strategy to fit the media than it can with DVD-R, consistently providing better burns. For comparison, DVD-R includes one profile, optimum power output based for that one profile only and uncalibrated towards what wavelength it is for, less precise laser power settings, and no other additional information. Typically, DVD-R burners have to already know how to burn a certain piece of media (and include this information in their firmwares) before they can properly burn to it. New media often is not properly supported. In addition to the optimum power control profiles, DVD+R also gives four times more scratch space for the drive to calibrate the laser on; more space can only improve the calibration quality. So, in short, DVD+R media exists to simply produce better burns and protect your data better.
Y porque: - se puede almaenar más info (programas)
- puedes borrar si no te gusta lo que has grabado
- la grabación es "más fiable" porque aseguras un flujo de datos constante a la grabadora
- ...
El hecho de poder borrar la información en cualquier momento es un inconveniente para ciertas aplicaciones, como las legales, en las que se debe asegurar que los datos históricos no se han alterado. ¿Leiste 1984? La historia se alteraba con fines de control del gobierno sobre la gente, alterando los registros históricos a conveniencia.
Sí, en los clientes de TV y seguridad que tenemos necesitan un sistema de archivado específico para eso que se llama "copia legal" y tienen que garantizar durante no sé cuánto tiempo la fiabilidad y la inmutabilidad de los datos. La banca y seguros también lo tienen.
Aunque claro, siempre se puede quemar un edificio ... ;)
Je! Se supone que debes tener dos edificios al menos, y bunkerizados, para esas aplicaciones. Creo que mi colegio de ingenieros alquila o lo que sea espacio de ese a un banco para guardar los proyectos (en PDF firmado).
Hace un mes, un cliente del mundo HPC me eneseñaba su primer cluster hecho con PCs. Le dije de broma que si se quería deshacer de toda esa metralla qu eme llamase que yo pasaba a recogerlo ;) Me dijo qu ela Ley le obliga a que los datos sean accesibles durante 20 años. Le dije que no quería los disocs duros y me dijo que no es eso, que el sistema tiene que arrancar y ser perfectamente funcional dentro de 20 años por temas legales y que no le apetecía migrar TODOS los datos al nuevo cluster así que se quedaba con el cluster antiguo.
¿Que tenía que garantizar el funcionamiento de los ordenadores con sus discos y todo dentro de 20 años? Imposible.
Me gustaría ver a los jueces, abogados, notarios y políticos que sacaron esa estúpida ley dentro de 20 años ... Como no estarán por aquí, les da igual: que apechugue el que viene detrás. Si es que les ponía yo a trabajar a todos a pleno sol ...
X'-)
Ah, por cierto, ya me ha mandado un email Seagate confirmando que me lo envían, y yo se lo mandé el lunes por Seur... Muy rápido. Podría tenerlo mañana con suerte.
A ver si hay suerte :)
Pues de momento, no ha llegado.
Hay DVDs de uso profesional para archivado permanente a 200 años. Y cuestan una pasta. La capa óptica es de "piedra".
Si valoras tus datos ...
Yo no tanto... lo que hago es tener dos, o más, copias. - -- Saludos Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAks7YQoACgkQtTMYHG2NR9UuwACfR8FE+8E5wSmUE3ALSvC55fcj QmIAoJUYyaYcSnv78TXUxv2yE8dE48ha =d9AN -----END PGP SIGNATURE-----