CompuServe Messages

Dan, The largest drive figures I'm aware of spin at about 4000 rpm and have upto 42 sectors per track. Presuming 1:1 interleave, that means in one minute, the drive head passes over 4000 x 42 sectors. 168000 sectors x 512 bytes per sector is 86,016,000 bytes per minute. Divide by 60 and you get 1,433,600 bytes per second. That does not take into account the drive doing anything except reading that one track over and over again. As soon as you get into head stepping, that number drops off rapidly. Now, a drive with a 64k cache *could* already have that data in the cache, thus isn't restricted by how fast the data comes under the head…but rather how fast the cache can be read and how fast it can be pumped over the bus. But presuming the data isn't in the cache, or that the amount of data you want is larger than the cache…then the rate that data can be read off the drive becomes the limiting factor since the cache can empty faster than it can be filled. You simply can't read data off the disk any faster than the data comes under the head (any one head…since that's all that can be read at once for the type of drives we're talking about here) when you are talking *sustained* rates. Burst rates…yes..and even relatively long bursts IF the data is already in the cache…but for larger files…spin rate and sectors per track is the limiting factor. Don