Disk80 tracks side 18 sectors track 512 bytes sector

/ disk)(80 tracks / side )(18 sectors / track )(512 bytes/ sector )
=1,474,560 Bytes/ disk
1.47 MB
Store data using Longitudinal Recording or Perpendicular Recording
Computing capacity
Multiply number of sides, # tracks, # sectors per track, # bytes per sector
For high density disk: 2 sides x 80 tracks x 18 sectors per track x 512 bytes per sector=1,474,560 bytes
The hard disk arms move the read/write head, which reads items and writes items in the drive
Location is often referred to by its cylinder
Head crash occurs when read/write head touches surface of platter
Always keep backup of your HD

RAID is a group of two or more integrated HD’s
Main benefit is availability of storage
Secondary is improved performance
NAS is server connected to network with sole purpose of providing storage
Disk controller consists of special purpose chip and electronic circuits that control transfer of data,
instructions, and info from disk to and from the system bus and other components of computer
SATA
EIDE
SCSI
SAS
Hard Disks vs Disk Cache
Portion of RAM memory that processor uses to store frequently accessed items
1
st
request for data goes to disk cache
2
nd
request goes to HD
Memory cards and USB Flash Drives (storage)
Digital photos or files to be transported
Optical disks
Software, movies, music
Consists of flat, round, portable disk made of metal, plastic, and lacquer that is written and read by a laser
Typically store software, data, digital photos, movies, music
Read only vs rewritable
How a laser reads data on optical disk:

1. Laser diode shines light beam toward a disk
2. If light strikes a pit, it scatters, if light strikes a land, it reflects back toward laser diode
3. Reflected light is deflected to a light sensing diode, which sends a digital signal of 1 to the computer.