rcstack@rw6.urc.tue.nl (Studenten Vereniging Stack) (04/05/91)
I'm looking for a 600 MB SCSI drive to replace my current 300 MB ESDI drive. Two possible candidates are a CDC/Imprimis/Seagate ST4766N or a HP 97548. I have enough information on the ST4766N drive but little on the HP drive. According to an ad by a local distributor the HP should be a 20Mb/s drive with an average access of 16ms. According to SCSICNTL the drive has 1457 cylinders with 16 heads and 57 sectors per track. This seems to indicate a data transfer of slighly above 15 Mb/s. So is 20 Mb/s the real transfer rate and if so why are there so little sectors per track. Thanks in advance, Jean-Paul Smeets -- ============================================================================= Email: Internet: rcstack@urc.tue.nl Bitnet: rcstack1@heitue5 Computer Association STACK, Computing Centre RC 1.82, Eindhoven University of Technology, POBox 513, 5600 MB Eindhoven, Holland.
prn@hpcpbla.HP.COM (Peter Nicholls) (04/08/91)
>According to an ad by a local distributor the HP should be a 20Mb/s drive >with an average access of 16ms. According to SCSICNTL the drive has 1457 >cylinders with 16 heads and 57 sectors per track. This seems to indicate a >data transfer of slighly above 15 Mb/s. So is 20 Mb/s the real transfer rate >and if so why are there so little sectors per track. There are two factors to take into account. The HP drive spins at 4002 rpm, and has an embedded servo. The burst transfer rate is the rate seen transfering one sector of data. The bit density of the data in the sector is equivalent to a 657 byte sector on a non-embedded servo. (58 bytes are used for the embedded servo). So... 657*57*8*4002/60 = 19,982,786 Close enough. The track transfer rate is quoted at 15.57 Mbits/s - which matches the figure above. The reduced transfer rate is one of the penalities of the superior reliability of embedded servo. Peter Nicholls -------------- European Disk Integration Engineering Hewlett-Packard Ltd., Bristol, ENGLAND. =============================================================================