The two main types of hard disk are IDE and SCSI. The former is probably the best choice for general use, whereas SCSI disks have certain advantages in networked and scientific installations.
Recent improvements in the way IDE disks work has led to the development of enhanced IDE (E-IDE) which makes hard disks faster at transferring information. E-IDE disks may be categorised as being able to use level 3 or level 4 data transfer. Level 4 is faster than level 3, and both are significantly faster than ordinary (non­enhanced) IDE.