Question: Suppose we have a harddisk with 2 platters with characteristics below:
?
Rotational rate: 10, 000 RPM ?Avg sectors/track: 1000 ?Surfaces: 4 ?Sector size: 512 bytes
I was reading “Computer Systems: A Programmer’s Perspective 2ed” when I found that it calculates transfer time as if it only uses ONE head to read a sector.If that’s the case, why not use 4 heads to write(read) on 4 surfaces? So when I write a 2K bytes file, each head should only need to wait for the platters to rotate just one sector length instead of 4, thus reducing the transfer time by a factor of 4.Or even redesign sector to make each sector on one cylinder but on 4 tracks residing same position respectively on 4 surfaces. Each one of (512/4) bytes. So when the hd needs to read a sector of 512 bytes, we only need the disk to rotate roughly 1/4 compare to original time. The idea looks like RAID 0.
Answer: To read or write all heads at once would require duplicating all the circuitry involved – head amplifiers, bitstream decoders, even the microprocessors and cache memory. I don’t know how disks are actually designed, but it seems unlikely to me, especially given the price pressures in the industry. Besides, even the stream from a single platter is likely to be near the interface limit – it’s the seeking and rotational delays that kill you.