On 6/21/2003 at 11:35 PM Lau wrote: >Back to my earlier mention of caching... hard drives and their >controllers do caching as well. I'm not certain if they do read-ahead >caching.
In short, yes. Even older IDE drives with sufficient buffer memory at least attempt to always read in the whole track if given time (no requests for sectors from another track within the time needed for a full revolution). However, the definition of a 'track' can vary - logical tracks (as addressed by the CPU) have very little to do with the physycal actuality, as most drives since the ra of 40Mb drives have constant linear bit density - i.e. outer tracks, being of a larger circumference, have more sectors. The drive does the translation into a uniform sector per track topology. Most drives do read ahead in terms of physical tracks, but in some cases (such as small buffers or odd translation schemes) will work in terms of logical tracks. In any case, the actual mechanism is hardly important and the implementation is is left to the drive manufacturer.
