When Sony launched the world's first Blu-Ray DVD recorder at a quiet Tokyo press conference recently, it could hardly have been more understated.

Sony PR staff told us they had no fixed expectations for sales and, a few weeks later, when we finally had a chance to review the BDZ-S77 for ourselves, they remained tight-lipped about how many units had actually been sold. Given that, why were AV cognoscenti worldwide beside themselves with excitement over what was essentially just another machine for recording television shows on to silver discs?

To answer the question, we need a brief glimpse into the little-understood world of High Definition Television (HDTV). Although not a new concept, HDTV is not something most UK residents will have seen, and therefore remains something of a mystery. A clearer picture composed of more horizontal lines sounds like a fine idea, but it's not exactly a compelling concept to the uninitiated and has been largely overlooked in favour of a wider channel selection, interactive broadcasts and a host of digital services, both terrestrial and satellite.

However, anyone lucky enough to actually sit in front of an HDTV broadcast, pumped out on a quality screen with a decent audio setup will tell you that it's worth more than a thousand channels of plain vanilla television. HDTV is not just about clearer pictures, rather it's a means to a certain level of immersion that can draw a viewer into the programme with a startling sense of reality. The heightened realism is so striking in HDTV broadcasts, they feel almost as if they're made up of razor-sharp 3D images.

So, if the bottom line is quality, why haven't we seen more HDTV? As with anything, quality costs money - from the huge development funds needed by the TV networks, to the cost of HDTV equipment levied on the end user, cash has held it back. In the US and Japan, countries where HDTV has taken off in only a small way, those early adopters who have laid down the readies are a vociferous bunch.

Take Dale Cripps, HDTV guru and publisher of HDTV Magazine. He told us why we are losing out compared to his stateside colleagues: "The European HDTV effort was scuttled by those who were planning a DBS (Direct Broadcast Satellite) future for Europe in 1990/91. They took a more 'cautionary' path, and arguments made then touched upon the idea that Europeans have less taste for TV."

Back to Japan in 2003, and we have the first application of Blu-Ray technology in the BDZ-S77. In a nutshell, it uses a blue laser, which can write more data to a disc (up to 23GB per side in Sony's case) than the red laser currently used in traditional DVD recorders can manage. To that increased capacity, Sony added a digital signal processor (DSP) that can handle a bit-rate of up to 36Mbps, which means that more information can be read from, or written to, the disc in a given time.

As you might assume, more information and faster speeds than your average DVD recorder equates to a far better onscreen picture. By comparison, standard DVD information is recorded at around 4Mbps. The upshot of all this cutting-edge engineering is the first machine capable of recording the Holy Grail - HDTV.

That's the theory, now for the practice, as witnessed in Sony's Tokyo labs on a high-end HDTV Trinitron. Initially, the most striking thing about the Blu-Ray recorder is its bulk - it weighs a hefty 14kg. Nonetheless, its imposing looks befit the £2,000 price tag. First off, we used the integral digital satellite tuner to find a suitable HDTV broadcast, in this case from NHK, which is Japan's equivalent of the BBC.

Slightly daunted by the staggering quality of the broadcast, we slotted in a caddy-protected Blu-Ray disc and recorded a few minutes at the highest bit-rate, which allows for around two hours of full-quality HDTV with Dolby 5.1 audio. Playback was literally perfect, with no quality loss whatsoever - which is a truly impressive result. Dropping down through the stepped recording levels, we repeated the feat at the lowest permissible quality, which squeezes 12 hours on to a disc.

At this level, the reach-out-andtouch quality of full HDTV was gone, with slight picture noise but a still excellent DVD-standard recording. The recording mode must be set manually, although it might have been an option for Sony to allow the machine to consult its electronic programme guide (EPG) and automatically work out how best to fit in the show you're recording.

For such a seemingly complex machine, the BDZ-S77 is actually a breeze to operate. The majority of functions can be accessed through a joystick on the foot-long remote handset, while those that can't are hidden under slider panels. The onscreen menu is Sony-slick and even provides indexing data for each recording on a disc. Recording is non-linear, via DVD-RAM or a hard drivebased recorder, which allows for simultaneous playback and recording and more efficient use of disc space.

Recordings can only be made on a Blu-Ray disc, but the machine can play any DVD, DVD-R/RW, CD, CD-R/RW or CD-DA. We played back a DVD and can report that the output was similar to HDTV recorded on the unit's long-play mode. Audio buffs are well catered for, with analogue, coax and optical digital outputs included. As you would expect at the price, composite, component and S-Video outputs are all present and correct.

Overall, if you're both in Japan and into HDTV in a big way, then the BDZ-S77 is a compelling option. It is expensive, and bear in mind that you'll need a digital satellite dish to secure something for the onboard tuner to decode, as well as an HDTV-capable display. Considering suitable TVs start at around £3,000 in Japan, you're looking at the thick end of five grand to get this impressive AV show on the road.