Toshiba Tecra 500CS User Manual page 296

000-book.bk : 14-nerd.fm5 Page 317 Wednesday, May 15, 1996 4:15 PM
The amount of data a diskette can hold depends on how it is for-
matted. In double-density format it holds 720 KB, in high-density
format it holds 1.44 MB. Your computer's diskette drive can han-
dle both formats.
A had disk holds as much data as several hundred diskettes. Your
computer's hard disk hold 1.265 gigabytes (1.358 billion bytes.)
How Big Is a Megabyte, Anyway?
You may be wondering what terms kilobyte, megabyte and
gigabyte mean. In normal metric terminology, kilo means thou-
sand, mega means million and giga means billion. But computer
terminology is different.
Computers use base two arithmetic, also called binary arithmetic.
Because of this, all numbers in computing are based on powers of
two. One megabyte is actually equal to 1,048,576 bytes (2
closest binary number to 1,000,000. One gigabyte is 1,024
megabytes.
Compact Discs
Like an audio CD, a CD-ROM is an optical storage medium. Data
is stored in concentric tracks on one side of the disc, and the read
head incorporates a laser beam.
Unlike hard disk drives, which rotate at a constant speed, a
CD-ROM drive changes its rotational speed according to which
part of the CD it is accessing. This allows the laser to read data at a
constant speed regardless of whether it is accessing an inner or an
outer track. Because of the momentum of the disc, this continuous
acceleration and deceleration means that accessing data is slower
than for a hard disk.
Your computer is supplied with a quadruple speed CD-ROM.
That means it rotates four times faster than an audio CD. How-
ever, the rotational speed of the drive is only one factor in the per-
formance equation. The size and type of the drive buffer, the head
movement mechanism and the type of interface all affect perfor-
mance.
Part I: Getting To Know Your Computer
If You Want to Know More
How Does a Disk Store Information?
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