Chapter 9: Hard Disks and Floppy Disks^189
Disk Capacities
Disk drive capacities are generally stated in megabytes and gigabytes, but drives with
terabyte capacity are beginning to appear. Table 9-2 lists the more common data capacity
units used with disk drives and their abbreviations. Just in case you’re curious, the next
two units after an exabyte are the zettabyte (1,000 exabytes) and the yottabyte (1,000
zettabytes). However, it will likely be a year or two before those capacities show up on
disk drives for PCs.
A typical hard disk drive purchased with a system today would likely be in the 4 to
30GB range, depending on the PC and how much you spend. To get more disk storage
space, you’d either have to add a second drive or switch the interface from IDE to SCSI.Hard Disk Performance
A number of performance metrics and indicators are available that you can use to choose the
best disk drive for your PC or your particular requirements. Most people never worry about
the detail performance criteria of their hard disk, provided it is doing the job. However, if a
hard disk hasn’t been doing the job, the performance specifications published by every hard
disk system manufacturer can hel pyou find just the disk for your particular need.Unit Abbreviation Capacity
Kilobit Kb One thousand bits
Kilobyte KB One thousand bytes
Megabit Mb One million bits
Megabyte MB One million bytes
Gigabit Gb One billion bits
Gigabyte GB One billion bytes
Terabit Tb One trillion bits
Terabyte TB One trillion bytes
Petabit Pb One quadrillion bits
Petabyte PB One quadrillion bytes
Exabit Eb One quintillion bits
Exabyte EB One quintillion bytesTable 9-2. Common Data Capacity Units