Blu-ray Disc

Overview:-


Blu-ray, also known as "Blu-ray Disc" (BD) is the name of a next-generation optical disc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's leading consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson). The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data.
Current optical disc technologies such as DVD, DVD-R, DVD-RW, and DVD-RAM employ a 650nm red laser, bond 0.6mm-thick discs and use lenses with a numerical aperture (NA) of 0.6. By employing a short wavelength (405nm) blue violet laser, the Blu-ray Disc successfully minimises its beam spot size, reducing the lens' NA to 0.85 and so making it possible to focus the laser spot with much greater precision. As a consequence, the Blu-ray Disc's tracking pitch is reduced to 0.32µm, less than half of that of a regular DVD, and the minimum mark length is 0.14-micron, down from DVD's 0.4-micron. In addition, by using a disc structure with a 0.1mm optical transmittance protection layer, the Blu-ray Disc diminishes aberration caused by disc tilt, allowing for disc better readout and an increased recording density.
As a result, data can be packed more tightly on a Blu-ray Disc than on a DVD. A single-layer disc can hold 25GB, which can be used to record over 2 hours of HDTV or more than 13 hours of SDTV. There are also dual-layer versions of the discs that can hold 50GB. All this on media that is the same physical size as a CD/DVD.
The track format of Recordable Blu-ray Disc is groove-recording, i.e., recording data only on groove or in groove tracks. For the groove recording method, lands are sandwiched between adjacent grooves to block heat transfer between the grooves during recording.








History:-

In the mid 1990s, commercial HDTV sets were finally starting to enter a larger market. However, there was no good, cheap way to record or play back HD content. Indeed, there was no media that could store that amount of data, except JVC's Digital VHS and Sony's HD Betacam.[4] However, it was well known that using lasers with shorter wavelengths would enable optical storage with higher density. When Shuji Nakamura invented practical blue laser diodes, it was a sensation, although a lengthy patent lawsuit delayed commercial introduction.[5]








Sony started two projects applying the new diodes: UDO (Ultra Density Optical) and DVR Blue (together with Pioneer), a format of rewritable discs which would eventually become Blu-ray Disc (more specifically, BD-RE).[6] The core technologies of the formats are essentially similar.
The first DVR Blue prototypes were unveiled at the CEATEC exhibition in October 2000.[7] Because the Blu-ray Disc standard places the data recording layer close to the surface of the disc, early discs were susceptible to contamination and scratches and had to be enclosed in plastic cartridges for protection. In February 2002, the project was officially announced as Blu-ray,[8] and the Blu-ray Disc Association was founded by the nine initial members.






Competition from HD DVD:-



The DVD Forum (which was chaired by Toshiba) was deeply split over whether to go with the more expensive blue lasers or not. In addition, the proposed Blu-ray Disc with its protective caddy was both expensive and physically different from DVD, posing several problems.[10] In March 2002, the forum voted to approve a proposal endorsed by Warner Bros. and other motion picture studios that involved compressing HD content onto dual-layer DVD-9 discs.[11][12] However, in spite of this decision, the DVD Forum's Steering Committee announced in April that it was pursuing its own blue-laser high-definition solution.[13] In August, Toshiba and NEC announced their competing standard Advanced Optical Disc.[14] It was finally adopted by the DVD forum and renamed HD DVD the next year,[15] after being voted down twice by Blu-ray Disc Association members, prompting the U.S. Department of Justice to make preliminary investigations into the situation.[16][17] Three new members had to be invited and the voting rules changed before the vote finally passed.
In the mean time, Sony spun off Professional Disc for DATA from the Blu-ray Disc project. It was essentially Blu-ray Disc with higher-quality media and components. The devices were too expensive for the consumer mass market. Instead, it was aimed at the professional data storage space market as a replacement for their line of 5.25" MO drives. It was announced in October 2003, with the first devices shipping in December of the same year.

Blu-ray Format:-
1 Physical Format
The physical format of the Blu-ray disc system, which follows the 780 nm CD and the 650 nm DVD, will be the last optical disc system using visible light. Based on this information, we decided to use the following basic optical disc parameters, knowing that the development wasn’t complete, in order to maintain the expectation of future progress:
the shortest wavelength is 400 nm, the highest value of NA is 0.85,
the reasonable substrate thickness of 0.1mm, and the wavelength is 400 nm (blue-violet).
A shorter wavelength was examined, but 400 nm was finally selected because a shorter wavelength causes a durability problem in the plastics of the Substrate Incident.
(Footnote: Durability of plastics for optical discs in a ultra-violet range, from a catalog of Nippon Zeon Co.)

As shown in the figure many plastics for optical discs or optical devices suddenly show a poor
transmission factor when under 400 nm. Furthermore, some are deteriorated by a phenomenon similar to sunburn.
The wavelength fluctuation during production must be considered. The tolerance is set so that wavelength does not fall below 400 nm. In conventional cases, the wavelength is temperature dependent (for 780 nm the dependency = ca. 0.3 mm/deg.; for 650 nm ca. 0.25 nm/deg.). In particular, when recorded on a film with a pigment series recording sensitivity dependent on wavelength, a number of developments were needed. However, a 400 nm GaN laser seems to have a wavelength with a very small temperature dependency compared with 780 nm and 650 nm lasers. The diameter of the concentrated beam is defined by the NA value of the objective lens .

1.3 Blu-ray Format
1.3.1 Physical Format
The physical format of the Blu-ray disc system, which follows the 780 nm CD and the 650 nm DVD, will be
the last optical disc system using visible light. Based on this information, we decided to use the following
basic optical disc parameters, knowing that the development wasn’t complete, in order to maintain the
expectation of future progress:
the shortest wavelength is 400 nm,
the highest value of NA is 0.85,
the reasonable substrate thickness of 0.1mm,
and the wavelength is 400 nm (blue-violet).
A shorter wavelength was examined, but 400 nm was finally selected because a shorter wavelength
causes a durability problem in the plastics of the Substrate Incident.
(Footnote: Durability of plastics for optical discs in a ultra-violet range, from a catalog of Nippon Zeon Co.)

Wavelength dependency on
transparency
From a datasheet of Nihon Zeon

As shown in the figure many plastics for optical discs or optical devices suddenly show a poor
transmission factor when under 400 nm. Furthermore, some are deteriorated by a phenomenon similar to
sunburn.
The wavelength fluctuation during production must be considered. The tolerance is set so that the
wavelength does not fall below 400 nm. In conventional cases, the wavelength is temperature dependent
(for 780 nm the dependency = ca. 0.3 mm/deg.; for 650 nm ca. 0.25 nm/deg.). In particular, when recorded on a film with a pigment series recording sensitivity dependent on wavelength, a number of developments were needed. However, a 400 nm GaN laser seems to have a wavelength with a very small
temperature dependency compared with 780 nm and 650 nm lasers.
The diameter of the concentrated beam is defined by the NA value of the objective lens.

Disc structure:-

Like its rival format HD DVD, Blu-ray uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared lasers at 650 nm and 780 nm respectively.
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity. (See Compact disc for information on optical discs' physical structure.

Laser and optics
Like its rival format HD DVD, Blu-ray uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared lasers at 650 nm and 780 nm respectively.
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity. (See Compact disc for information on optical discs' physical structure.



Blu-ray Disc, DVD and CD compatible, 3-wavelength recording/playback Optical Head:

A single 3-wavelength recording/playback optical head, capable of recording and playing-back 3 formats,
Blu-ray Disc (BD), in addition to DVD, CD has been developed.
The BD market is expected to expand in the coming era as high-quality content becomes mainstream.
However, it is desirable for the BD recorder to record and playback DVD-R and CD-R. In order to cope with
this, a 3-wavelength recording/playback optical head is required.
To achieve a 3-wavelength recording and playback optical head with most simple structure, a single unit
3-wavelength laser and also an objective lens corresponding to the 3 wavelengths have been developed.
Utilizing the laser and the objective lens, a prototype optical head was made to realize a common optical
path for the 3 wavelengths. A picture of the prototype is shown in Figure 4.9.1. The prototype is 82 mm
in height, 50 mm in width and 32 mm in depth.





A diagram of the prototype is shown in Figure 4.2.9.2. In addition to the 3-wavelenght laser and
objective lens, a variable magnification function is key to realize the 3-wavelength optical head. The
function was realized by introducing expander lens assemblies whose magnifications were different for
corresponding objective lens apertures for BD, DVD and CD. With this function, the efficiency from each
laser to BD, DVD and CD can be maximized, enabling high speed recording for each format



Software standards


Codecs
Codecs are compression schemes that store audio and video more efficiently, either giving longer play time or higher quality per megabyte. There are both lossy and lossless compression techniques.
The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and the movie-software (content). For video, all players are required to support MPEG-2, H.264/AVC, and SMPTE VC-1. MPEG-2 is the codec used on regular DVDs, which allows backwards compatibility. H.264/AVC was developed by MPEG and VCEG as a modern successor of MPEG-2. VC-1 is another MPEG-4 derivative codec mostly developed by Microsoft. BD-ROM titles with video must store video using one of the three mandatory codecs. Multiple codecs on a single title are allowed.
The choice of codecs affects the producer's licensing/royalty costs, as well as the title's maximum runtime, due to differences in compression efficiency. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high-definition content on a single-layer (25 GB) BD-ROM. The more advanced video codecs (VC-1 and H.264) typically achieve a video runtime twice that of MPEG-2, with comparable quality.
For audio, BD-ROM players are required to support Dolby Digital AC-3, DTS, and linear PCM. Players may optionally support Dolby Digital Plus, and lossless formats Dolby TrueHD and DTS HD. BD-ROM titles must use one of mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.[47]
For users recording digital television programming, the recordable Blu-ray Disc standard's datarate of 54 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). For Blu-ray Disc movies the maximum transfer rate is 48 Mbit/s (1.5x) (both audio and video payloads together), of which a maximum of 40 Mbit/s can be dedicated to video data. This compares favorably to the maximum of 36.55 Mbit/s in HD DVD movies for audio and video data.





Java software support




At the 2005 JavaOne trade show, it was announced that Sun Microsystems' Java cross-platform software environment would be included in all Blu-ray Disc players as a mandatory part of the standard. Java is used to implement interactive menus on Blu-ray Discs, as opposed to the method used on DVD video discs, which uses pre-rendered MPEG segments and selectable subtitle pictures, which is considerably more primitive and less seamless. Java creator James Gosling, at the conference, suggested that the inclusion of a Java Virtual Machine as well as network connectivity in BD devices will allow updates to Blu-ray Discs via the Internet, adding content such as additional subtitle languages and promotional features that are not included on the disc at pressing time. This Java Version is called BD-J and is a subset of the Globally Executable MHP (GEM) standard. GEM is the world-wide version of the Multimedia Home Platform standard







Player profiles:




The BD-ROM specification defines four profiles of Blu-ray Disc players; in addition to the three listed in the table below, there is a fourth audio-only profile that does not require video decoding or BD-J.[57] All the video-based profiles are required to have a full implementation of BD-J, but with varying levels of hardware support.
Virtual file system

^ a This is used for storing audio/video and title updates. It can either be built in memory or removable media, such as a memory card or a USB flash memory.
^ b A secondary audio decoder is typically used for interactive audio and commentary
On November 1, 2007, the Grace Period Profile was superseded by "Bonus View" as the minimum profile for new players released to the market.[59] With the exception of the PlayStation 3, profile 1.0 players cannot be upgraded to be Bonus View compliant.[60] On December 17, 2007, the PlayStation 3 became Bonus View 1.1 compliant through PlayStation 3 System Software version 2.10.[61]
When software authored with interactive features dependent on "Bonus View" hardware capabilities are played on profile 1.0 players some features may not be available or may offer limited capability. Profile 1.0 players will still be able to play the main feature of the disc, however.



Backward compatibility:-






While it is not compulsory for manufacturers; the Blu-ray Disc Association recommends that Blu-ray Disc drives should be capable of reading standard DVDs for backward compatibility. For instance, Samsung's first Blu-ray Disc drive can read CDs, regular DVDs, and Blu-ray Discs. All other Blu-ray Disc players released are also capable of DVD playback, though not all support CD playback. This includes Sony, Panasonic, Philips, LG, Pioneer and PC-based players from Alienware, Sony, and Dell.





List of Blu-ray Disc devices:






























Corporate support:



Blu-ray Disc has gained a large amount of support in the corporate world,[63] with companies such as Apple, Dell, and Panasonic backing it. Blu-ray Disc was started by Hitachi, LG, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, and Thomson in February 19, 2002, with Panasonic, Sony, Pioneer, and Philips as the back-bone of the foundation.[64] Several members of the Blu-ray organization's Board of Directors who had originally pledged to support Blu-ray Disc later also supported HD DVD, such as Hewlett-Packard, Samsung, and LG.








Studio alliances:



Among the movie studios, Blu-ray Disc is currently exclusively supported in the United States by Sony Pictures Entertainment and MGM (20% of MGM's stake is owned by Sony) as well as Disney, 20th Century Fox, Warner Bros. Pictures, New Line Cinema[67] and Lionsgate, representing over 70% of home video marketshare.





On August 20, 2007, Paramount Pictures, DreamWorks Pictures and DreamWorks Animation, announced they would no longer be supporting the Blu-ray Disc format. However, Paramount reserves the right to switch its backing to Blu-ray Disc.[69] Citing HD DVD's lower consumer equipment and disc replication costs (due to its similarities to the standard DVD format), all future Paramount/Dreamworks titles will be released exclusively on HD DVD. Together, Paramount and DreamWorks are currently the 2007 box office leaders.[70][71] Movies directed by Steven Spielberg are not included in this announcement, as Spielberg controls his films.[72] In an interview with PC World, Alan Bell, the Executive Vice President and Chief Technology Officer for Paramount Pictures, stated the exclusive support for HD DVD is currently indefinite.[73] However, two Viacom executives who spoke to the New York Times disclosed that the terms of the agreement were for $150 million in incentives in exchange for an exclusivity period of at least 18 months, or through the next two holiday seasons.[74] In response to these reports of a $150 million deal, DreamWorks Animation CEO Jeffrey Katzenberg stated that it was disingenuous for other companies to suggest that they were not compensated for endorsing Blu-ray.[75]
Warner Brothers Pictures, initially in the HD DVD camp, later decided to support both formats. However, on January 4, 2008, they announced that they would discontinue HD DVD support as of June 1, 2008. Furthermore, they intend to delay remaining HD DVD titles until after standard DVD and Blu-ray releases.[76] Warner Brothers has also scheduled all of their HD DVD exclusive titles for release on Blu-ray in the near future. Warner Brothers' subsidiary New Line Cinema has followed suit, cancelling tentative plans to release titles on HD DVD contingent on region coding.[67][77][78] Various news outlets have speculated that Warner Brothers' decision will effectively end the nearly two year long format war with HD DVD.[79][80][81] The HD DVD group responded to the decision by stating, "We remain firm in our belief that HD DVD is the format best suited to the wants and needs of the consumer." On January 8th, 2008, the Financial Times reported that Paramount was poising to use an escape clause in their exclusivity agreement with HD-DVD in light of Warner's recent announcement. [82]
Outside of the United States, movies from American studios are often distributed by different companies (e.g. StudioCanal in Europe). Thus many of these Blu-ray exclusive titles are available outside the U.S. on HD DVD.[83] Likewise, movies that are exclusive to HD DVD in the United States have Blu-ray releases in other regions. An example of this is the Universal Studios film Bruce Almighty, which has been released exclusively on HD DVD in the U.S., but has been released as a Blu-ray exclusive in Europe due to the distribution rights held by Buena Vista.[citation needed] Many Blu-ray discs are multi-region, making import of these titles easier.







Blu-ray Disc / HD DVD comparison:-




The primary rival to Blu-ray disc is HD DVD. Due to the format war, both sides are currently vying to promote their format as the best choice for studios and consumers. The technical details of each format do not differ much and should not affect the average consumer. Both formats are superior to DVD and produce quality HD video playback.
There is no Region Coding in the existing HD DVD specification; titles from any country can be played in any player. Some Blu-ray discs have Region Coding and will only play in players sold in the corresponding geographic region.
An estimated 1.97 million HD DVD discs have been sold between spring of 2006 and September 2007, compared to 3.01 million Blu-ray discs.[98] Sales of these two high-def disc formats accounted for only 2.5% of overall disc sales during the first half of 2007.





Blu-ray Discs and Cartridges:



BD-RE V1.0 disc uses a cartridge in order to prevent harmful fingerprints. After the BD-RE V1.1, BD-R V1.0, and BD-ROM V1.0, all types of discs should be used without a cartridge thanks to the progress of the hard-coating technology described in 1.6. Only for special applications or for severe environments, a cartridge may be used.
Two kinds of Blu-ray cartridges had been defined, as shown in the figures below. As seen in Fig.
1.7.1-1.7.4, one has an opening for a printed surface and the other has an entirely sealed cartridge structure. The shielded cartridge was an option until August 31, 2003 and should not be used anymore. It should be possible to remove the disc from the cartridge.
With respect to the open type cartridge, the mechanism for releasing the disc can be freely designed by the manufacturer of the cartridge as long as the cartridge fulfills all specifications.





This cartridge has a mechanism to latch the disc. The latch is not released until a disc is inserted. The
recording side is closed. When latched, the disc is in close contact with the cartridge at the inner and outer
perimeters to prevent dust. Data shown in the figure is a prediction for ten years of usage assuming a
typical home environment. The error rate is far below the standard rate of 4.2E-3 per byte for Blu-ray
(shown by the red line in the figure), and this durability is regarded as sufficient. It is expected that Blu-ray
Discs can be treated a little more roughly, like VTR tapes, by adopting the cartridge.
The mechanism for releasing the disc can freely be designed by the manufacturer of the cartridge as
long as the cartridge fulfills all specifications.







Ongoing development:-




Although the Blu-ray Disc specification has been finalized, engineers continue working to advance the technology. Quad-layer (100 GB) discs have been demonstrated on a drive with modified optics (TDK version) and standard unaltered optics ("Hitachi used a standard drive.").[100][101] Hitachi stated that such a disc could be used to store 7 hours of 32 Mbit/s video (HDTV) or 3.5 hours of 64 Mbit/s video (Cinema 4K). Furthermore TDK announced in August 2006 that they have created a working experimental Blu-ray Disc capable of holding 200 GB of data on a single side, using six 33 GB data layers.[102]
Also behind closed doors at CES 2007, Ritek has revealed that they had successfully developed a High Definition optical disc process that extends the disc capacity of both competing formats to 10 layers. That increases the capacity of the discs to 250 GB for Blu-ray compared to 170 GB (HD DVD now permits 17GB per layer[citation needed]) for HD DVD using the same process. However, they noted that the major obstacle is that current reader and writer technology does not support the additional layers.[103]
JVC has developed a three layer technology that allows putting both standard-definition DVD data and HD data on a BD/DVD combo. If successfully commercialized, this would enable the consumer to purchase a disc which could be played on current DVD players, and reveal its HD version when played on a new BD player.[104] This hybrid disc does not appear to be ready for production and no titles have been announced that would utilize this disc structure.
In January 2007, Hitachi showcased 100 GB Blu-ray Disc, which consists of four layers containing 25 GB each.[105] Unlike TDK and Panasonic's 100 GB disc, this disc is readable on standard Blu-ray drives that are currently in circulation, and it is believed that a firmware update is the only requirement to make it readable to current players and drives




Comparison of high definition optical disc formats:-

Future:-

Fluorescent Multilayer Disc

Fluorescent Multilayer Disc (FMD) was an optical disc format developed by Constellation 3D that uses fluorescent, rather than reflective materials to store data. Reflective disc formats (such as CD and DVD) have a practical limitation of about two layers, primarily due to interference, scatter, and inter-layer cross talk. However, the use of fluorescence allowed FMDs to operate according to the principles of 3D optical data storage and have up to 100 data layers. These extra layers potentially allowed FMDs to have capacities of up to a terabyte, while maintaining the same physical size of traditional optical discs A 50 GB prototype disc was demonstrated at the COMDEX industry show in November 2000. First generation FMDs were to use 650 nm red lasers, yielding roughly 140 GB per disc. Second and third generation FMDs were to use 405 nm blue lasers, giving capacities of up to a terabyte.
After Constellation 3D shut down due to a scandal (the scandal essentially involved the prototype "demonstrated" at COMDEX 2000 being a hoax — the content was actually playing on a hard drive — the device was faked) and the company consequently ran out of money.

Holographic Versatile Disc

Holographic Versatile Disc (HVD) is an optical disc technology which would hold up to 3.9 terabytes (TB) of information. It employs a technique known as collinear holography, whereby two lasers, one red and one green, are collimated in a single beam. The green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data.
A dichroic mirror layer between the holographic data and the servo data reflects the green laser while letting the red laser pass through. This prevents interference from refraction of the green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology.[1] These discs have the capacity to hold up to 3.9 terabytes (TB) of information, which is approximately 5,500 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray Discs, and about 4 times the capacity of the largest computer hard drives as of 2007. The HVD also has a transfer rate of 1 Gbit/s (128 MB/s). Optware was expected to release a 200 GB disc in early June 2006, and Maxell in September 2006 with a capacity of 300 GB and transfer rate of 20 MB/s.[2] Since the announcement, there have been no further news or products on market.

Protein-coated disc:-

protein-Coated Disc (PCD) is a theoretical optical disc technology currently being developed by Professor Venkatesan Renugopalakrishnan, formerly of Harvard Medical School and Florida International University. PCD would greatly increase storage over Holographic Versatile Disc optical disc systems. It involves coating a normal DVD with a special light-sensitive protein made from a genetically altered microbe, which would in principle allow storage of up to 50 Terabytes on one disc. Working with the Japanese NEC Corporation, Renugopalakrishnan's team has created a prototype device and estimate that a USB disk will be commercialised in 12 months and a DVD in 18 to 24 months as of July, 2006[1].
The technology uses the photosynthetic pigment bacteriorhodopsin created from bacteria.

The information in such discs would be highly dense, due to being stored in proteins that are only a few nanometres across. However, a method to address individual protein molecules to read and write information to and from them would have to be developed in order to achieve the theoretical 50 TB capacity. Practically, capacity would probably be limited by the size that addressing light can be focused to, so a DVD-sized disc might be able to hold ~50 GB, or perhaps ~240 GB if nearfield optics were used.