The speed of a hard disk drive determines the number of tracks that can be played simultaneously.
The rotational speed is the most important factor. Disks of 7200 rpm are good for audio, 10,000 rpm even better.
The technology used to interface the hard disk drive to the computer or other recording system is also significant.
SCSI is the fastest, ATA and Firewire are not yet as fast, although they are usable for up to 24 simultaneous tracks.
For the greatest track count, multiple disks are often used.
There are certain factors that limit track count:
- Edit density - the more the audio is edited and scattered, then the more the hard disk drive has to search for each segment. The harder it has to work, the slower it will retrieve the audio.
- Using variable speed (varispeed) to increase the playback speed will increase the data rate. It is usual for hard disk recording systems to be able to play back much slower than real time, but rarely can they play more than around 6% faster, and even this might limit the track count.
- If a higher data rate is used, for 24-bit recording rather than 16-bit, or for 96 kHz sampling rather than 44.1 kHz, then correspondingly fewer tracks will be able to play simultaneously.