Investigating Data Processing Understanding Memory

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MAC OS


Unit A

Page: 10
-
11, 12
-
13

Investigating Data Processing


Understanding Memory

Data Files


Data

is the information processed in a computer *words,
graphics, numbers and figures*.


All data and programs are stored as
files
.

There are three kinds of files:


A
computer file
is a named collection of stored data.


An
executable file
contains the instructions that tells a
computer how to perform a certain task.


A
data file
is created by a user, usually with software. (Example:
the report you create with word processing needs to be saved as
a data file to be accessed later.)


Data Processing Binary Representation


The characters used in human language are meaningless to a computer.



A computer represents information as numbers called
binary numbers
.
There are two numbers that a computer uses , “0” and “1”.



These two numbers are called
bits
.


A group of
8 bits
is called
byte
. Figure A
-
12, page 11


Each number should be represents with 8 bits.


Example: the number 1 is represented as
000 0001


The number 2 is represented as
000 00010

The
smallest

number for a computer is
0 (000 000 00)
and the
largest

number
is
255 (111 111 11
)


KB, MB, GB


A
kilobyte

(KB) is 2024 bytes.


A
megabyte

(MB) is about one million bytes


A
gigabyte

(GB) is about one billion bytes.


A
Terabyte

(TB) is about one trillion bytes.

ASCII


Personal computers use the
ASCII

system to represent
character data.


ASCII
: American Standard Code for Information Interchange


Each
ASCII

number represents an
english

letter. Computers
translate
ASCII

into
binary data
so that they can process it.
Figure A
-
13, page 11


ASCII Representation


The
ASCII

system used
7 bits
to represent the numbers
0 (000
0000)

through
127 (111 1111).
The numbers are for characters
and non printing characters (Enter, space). The
8
th

bit
is used
for
error checking
.


Numbers
128 (1000 0000)
through
255 (111 111 11)
is used to
represent additional characters and symbols. This is the
extended ASCII
system
ex:
$, ©.


Refer to figure A
-
13 on page 11 to study the difference
between ASCII and binary digits.

Understanding Memory


One of the most important computer’s hardware is the
memory
, which stores instruction and data.



There are
five

types of memory:


Random Access Memory


Cache Memory


Virtual Memory


Read
-
only Memory


Complementary Metal Oxide Semiconductor Memory




Random Access Memory
-

RAM

1.
Random Access Memory (RAM)
temporarily stores programs
and data while the computer is on to allow the computer to
access these information randomly.

2.
RAM

doesn't

t need to access data in the same sequence in
which it was stored.

3.
The characters you type are stored in RAM with fonts, graphics
and other objects.

4.
RAM

consists of chips on
cards

that are plugged into the
motherboard
.

RAM


Most personal computers use some type of
synchronous
dynamic access memory
(
SDRAM
) which is synchronized
with the processor to allow faster access to its contents.


RAM

is referred to
volatile

or
temporary

memory because it
is
constantly changing
as long as the computer is on and is
cleared

as soon as the computer is shut off.


Memory capacity
is also referred to as
storage capacity
which is the amount of data that the computer can handle at
any given time and is measured in
megabytes or gigabytes
.

Cache Memory


Sometime called
RAM cache
or
CPU cache
is a special, high
-
speed
memory chip
on the
motherboard

or CPU itself that
stores frequently accessed and recently accessed data and
commands.



Virtual Memory


Virtual Memory
is a space on the computer’s storage devices
that stimulates additional RAM.


It enables the programs to run as if your computer had more
RAM

by moving data and commands from RAM to the hard
drive and swapping in the new data and commands.


Virtual RAM
is much
slower

than the
RAM
.


Read
-
Only Memory
-

ROM


Read Only Memory
is a chip on the motherboard that has
been prerecorded with data.


ROM

permanently

stores the set of instructions that the
computer uses to check the computer system’s components
to make sure they are working and to activate the essential
software that controls the processing functions when you
turn the computer on.


ROM


ROM

contains a set of instructions called
BIOS

(
Basic Input Output
System
) which tells the computer to initialize the
motherboard
,
how to recognize
peripherals

and to start the
boot process
.


Boot Process
is the set of events that occurs between the moment
you turn the computer on till the moment you start to use the
computer.


The
instructions

used to execute the
boot process
is saved in the
ROM
.


ROM never changes and remains the same when the computer is
turned off. Therefore, it is
nonvolatile

or
permanent

memory.

Complementary Metal Oxide
Semiconductor Memory
-

CMOS


Complementary Metal Oxide Semiconductor Memory
(
CMOS
) is
installed on the motherboard that is activated during the
boot
process
and identifies where essential software is stored.


A small rechargeable battery
powers the
CMOS

so its contents are
saved when the computer is turned on. CMOS changes every time
you add or remove hardware on your computer system


CMOS

also referred to
semi permanent memory
changes when the
hardware is added or removed but doesn't

t empty when the
computer is turned off.


Because
CMOS

is not cleared when the computer turns off, the data
and time are stored there.


Figure A
-
14 page 13