Introduction to Computers, the Internet and Java - Java: How to Program Early Objects - page 5

Similar growth has occurred in the communications field—costs have plummeted as
enormous demand for communications bandwidth (i.e., information-carrying capacity)
has attracted intense competition. We know of no other fields in which technology
improves so quickly and costs fall so rapidly. Such phenomenal improvement is truly fos-
tering the Information Revolution .

1.2.2 Computer Organization
Regardless of differences in physical appearance, computers can be envisioned as divided
into various logical units or sections (Fig. 1.2).

Logical unit Description

Input unit This “receiving” section obtains information (data and computer programs)

from input devices and places it at the disposal of the other units for pro-
cessing. Most user input is entered into computers through keyboards,
touch screens and mouse devices. Other forms of input include receiving
voice commands, scanning images and barcodes, reading from secondary
storage devices (such as hard drives, DVD drives, Blu-ray Disc™ drives and
USB flash drives—also called “thumb drives” or “memory sticks”), receiving
video from a webcam and having your computer receive information from
the Internet (such as when you stream videos from YouTube ® or download
e-books from Amazon). Newer forms of input include position data from a
GPS device, and motion and orientation information from an accelerometer
(a device that responds to up/down, left/right and forward/backward accel-
eration) in a smartphone or game controller (such as Microsoft ® Kinect ®
and Xbox ® , Wii™ Remote and Sony ® PlayStation ® Move).

Output unit This “shipping” section takes information the computer has processed and

places it on various output devices to make it available for use outside the
computer. Most information that's output from computers today is dis-
played on screens (including touch screens), printed on paper (“going
green” discourages this), played as audio or video on PCs and media players
(such as Apple's iPods) and giant screens in sports stadiums, transmitted
over the Internet or used to control other devices, such as robots and “intel-
ligent” appliances. Information is also commonly output to secondary stor-
age devices, such as hard drives, DVD drives and USB flash drives. A
popular recent form of output is smartphone vibration.

Memory unit This rapid-access, relatively low-capacity “warehouse” section retains

information that has been entered through the input unit, making it
immediately available for processing when needed. The memory unit also
retains processed information until it can be placed on output devices by
the output unit. Information in the memory unit is volatile —it's typically
lost when the computer's power is turned off. The memory unit is often
called either memory , primary memory or RAM (Random Access Mem-
ory). Main memories on desktop and notebook computers contain as much
as 128 GB of RAM. GB stands for gigabytes; a gigabyte is approximately
one billion bytes. A byte is eight bits. A bit is either a 0 or a 1 .

Fig. 1.2 | Logical units of a computer. (Part 1 of 2.)