lecture16

hard drives

host adapter interface versus controller

host adapter typically one of:

• IDE
• SCSI
• HIPPI = High Performance Parallel Interface;
  HPI = High Performance Interconnect, typically used for networking between supercomputers at 800mbytes/sec or 1600mbytes/sec over a 30 meter span with copper braided differential conductors (ribbon cable) or 10km with fiber.
  originally designed for high-speed interconnections between processors. recently extended to connect fast I/O devices as well.
  high cost ($80k for 80Gbytes).
  used for imaging. video editing, etc..
  for use with fast computer, e.g. dec alpha, or dual processor octane (r12000)
• Fibre Channel

note that a drive controller cache is ok for short bursts, but doesn't help much for video.

voice coil follows the servo track: tracks the servo track during heating and cooling of drive.

some drives (e.g. PCMCIA) have constant linear velocity, while most have constant angular velocity.

with constant angular velocity, it is better to put more data on the outer (larger) tracks than the inner tracks.

accordingly, CHS is fiction.

difference between hard drives and floppy drives: heads don't touch medium (platters) in hard drives, but heads touch medium in floppy drives.

some hard drives are (or contain, depending on your point of view) removable media...

encoding for disk storage media

manchester code

1. data and clock signals are combined to form a single self-synchronizing data stream,
2. each encoded bit contains a transition at the midpoint of a bit period,
3. the direction of transition determines whether the bit is a "0" or a "1," and
4. the first half is the true bit value and the second half is the complement of the true bit value.

manchester codes are used in enthernet (HDLC frames) in addition to disk drives.

manchester university

ece385 lab9 hall of fame

a few people have been asking about imaging, pictures, etc..