computer: a device that accepts input, processes data, stores data,
and produces output.
Draw a picture of computer
words and symbols in a document, numbers for a
pictorial input, audion signals from a microphone, mouse clicks from
a mouse, instructions for a process:
input devices: keyboard, mouse, scanner, digitizer tablet, microphone
(speech input), bar code scanner
processing of raw data done by central processor (CPU): electronic
circuitry in form of computer chips. Performs arithmetic operations
(add, multiply, subtract, divide) at incredible speeds 109 operations
per second. Also, performs comparisons of two numbers stored in
memory (which is larger, which is smaller, are they equal). Based on
these comparisons, CPU chooses from among alternatives and decides
whether to continue a repetetive operation or to stop.
Computer stores data in memory (main and secondary). kinds of data
stored: any of the input data we mentioned earlier. Normally the
instructions for a process are stored as well as the raw data to use
in the processing. -- Stored program computer/Von Neumman
computer. Each memory cell has unique address (fixed) but its
contents can change (memory is volatile).
Main memory directly accessible by the central processor - secondary
memory is not. All data and instructions must be moved into main
memory to be processed. Main memory is limited in size - up to 32
Megabytes for many computers. Seconday memory is not limited. Can be
expanded almost indefinitely by removable storage media - disks,
tapes, CD ROMs.
Main memory is not permanent memory - contents disappears when
computer is turned off. Secondary memory (storage in book) is semi-
permanent - data stays on disk until you erase it.
Bring a couple of disks to class - floppy disks 3.5 inches - IBM
high density - 1.44 Megabytes
ouptut devices - screen, printer, plotting device - draws graphs,
To compute a water bill: