The STORit box is equipped with abundant
local storage: a 50 GByte internal hard disk, capable of storing roughly 20 hours of
broadcast quality MPEG-2 video. Other types of data are negligible in terms of storage
space when compared to broadcast quality video. Removable media such as tapes or optical
discs are possible but were not used in the IBC demo.
In the demonstrator set-up, the STORit box is implemented on a PC, using external set-top
boxes for DVB reception and MPEG-2 playback, so the whole set-up has the appearance of a
laboratory prototype, rather than that of a finished product.
STORit box platform
For the STORit box, we have re-used experience, software and hardware from the SMASH project, in which several of the STORit partners participated previously. For this reason, we have again chosen Linux as our operating system. The arguments that lead to this choice in the SMASH project (superior multi-tasking, better device driver development for custom-made hardware, easier access to low-level PC internals), still hold today.
Storage devices
The main requirements for storage in the STORit box are:
In the requirements on video storage, one recognises the fridge - freezer metaphor: a sufficient amount of video is available ready for consumption in the fridge (hard disk), and an infinite supply can be found in the freezer (removable media).
Hard disk
Obviously, the requirements on fast and random access storage mentioned above can only be met by hard disks. The 2 GByte capacity used for regular data is no problem at all, but even the 10 hours of video storage (typically equivalent to 20 GByte) can nowadays be realised on a single hard disk. Hard disks up to 50 GByte are now commercially available, and there is no sign that the rapid development that has characterised the hard disk industry over the past 15 years will come to an end within 5 years. In fact, if we extrapolate the growth of hard disk capacity, as is shown in Table 1, even a conservative estimate leads to an impressive amount of video on a relatively cheap hard disk in the foreseeable future.
| Year | Video storage capacity |
| 2000 | 4 hours |
| 2005 | 40 hours |
| 2010 | 400 hours |
Table 1 : Video
content stored on a hard disk for $100, assuming 5 Mbit/s video data rate,
and a disc capacity doubling every 18 months (a conservative estimate)
The other key parameters of hard disks are
sustainable data rate and access time. On both accounts, even cheap present-day hard disks
are more than adequate to enable simultaneous recording and playback - one of the nicest
features developed in SMASH, which we certainly want to retain.
The main disadvantage of hard disks is that they are not removable, so exchanging
materials with other systems is not possible with hard disks only. From a security point
of view, this can be seen as an advantage: content stored on the hard disk cannot easily
be taken to another box. From a consumer point of view, a hard disk based system must
always be equipped with some removable medium. Of course a copy protection system will
prevent illegal copying from hard disk to removable media.
Tape
The removable medium with the largest
storage capacity available today is magnetic tape. Two tape drives are being used in
STORit: Tandberg and D-VHS.
Tandberg, manufacturer of computer tape drives and STORit partner, has a line of linear
tape drives (the 'MLR' and 'SLR' series), that rapidly develops in terms of capacity and
data rate. In just a few years, the performance will increase to a 100 GByte capacity
and a 15 MByte/s data rate, sufficient for storing 50 hours of standard
definition digital video, and for recording and/or playing back several streams
simultaneously. The downside of tape, of course, remains its relatively slow access. But
even that is expected to improve to well below 30 seconds, worst case.
The most important tape in the consumer electronics world is VHS, which now has its
successor in DVHS, the digital version of the same cassette. The current system features a
44 GByte storage capacity and a 1.7 MByte/s data rate. A factor of two improvement in
both aspects is foreseen.
In summary, we may expect in the near future tape systems with storage capacity for up to
50 hours on a single cassette, and with an access time of half a minute.
Optical disc
As has happened in audio, optical disc
systems are expected to replace tape in video applications as well. At the moment, two
optical disc technologies are commercially available: magneto optic (MO) and DVD-RAM. Both
are currently available with a capacity of 2.6 GByte per side (i.e. just over 1 hour
of video), double sided. The data rate varies between 1 and 3 MByte/s, and the access
time is typically 50-100 ms (full stroke). Within the time frame of the STORit
project, these figures may be expected to improve to 5 GByte per side, up to
5 MByte/s data rate and 25-50 ms access time.
In comparison to tape, the main advantage of optical discs is of course their faster
access. Though still not as fast as hard disks, in the perception of a consumer the system
will respond 'immediately'. The storage capacity is well below that of tapes, but at least
the volumes may be expected to hold an entire movie per side in the foreseeable future.