TV tuning performance under MCE
Windows XP (including Media Center Edition 2005) uses a generic driver model called Broadcast Driver Architecture (BDA) to allow software applications to access hardware and tune television. The BDA driver for a hardware tuner exposes the correct interfaces to the software, to allow tuner applications to search for and tune television signals. Additionally, the BDA driver must present MPEG-2 AV due to MCE's MPEG-2 processing core.Windows XP Media Center Edition 2005 therefore requires a compatible tuner to have an installed BDA driver before it will work correctly and use it for TV. ATI supplies a full BDA driver for its AIW products, including those with digital TV tuners, so that MCE 2005 can use them.
The BDA driver model means that multiple tuners can be installed simultaneously, and the 'Emerald' Update Rollup for MCE 2005 allows for four tuners (two analogue, two digital) to coexist in the same MCE 2005 system. Enterprising users can circumvent those limits, though. Multiple tuners allows for simultaneous watching and recording from entirely different channels.
In theory, installing multiple AIWs should give you access to the tuning resources of all. However, installing AIW Radeon X1800 XL and AIW Radeon X1900 in the same system proved to be a fruitless endeavour, at least under MCE 2005.
CPU utilisation while watching and recording
For this test, the Theater 550 PRO tuner was the watching device. CPU utilisation was monitored for each of the three digital tuners (installed and tested separately, of course) over a 30 minute period (recording from BBC1 broadcast over UK Freeview each time), as they recorded to disk to be watched later. BBC2 was watched, terrestrial analogue of course, on the Theater 550 Pro at the same time as the recordings were taking place.
The pair of AIWs have almost identical CPU usages, the differences in which can mostly be explained by the differences in TV being tuned. The DigiTV has lower CPU utilisation than both, despite having no hardware MPEG-2 encoding ability, indicating less software overhead.
That said, usage spikes are comfortably under 50% for both AIWs and average usage is hardly high, although it is a dual-core processor being used.
CPU utilisation while only watching
BBC1 was watched using the three DVB-T tuners while CPU usage was monitored.
Acceptable spikes and average usage numbers from all tuners were recorded in this test.
