PCs ENVIRONMENT and
PERIPHERALS
Lecture 3
MEMORY
 What is a memory ?
• Temporary storage place for data, instructions, and information
• Consists of one or more chips on the motherboard or some other
circuit board
operating system and other system software that
control the usage of the computer equipment

Three basic items
stored in memory:
application programs that carry out
a specific task
data being processed by application
programs
MEMORY
How are bytes stored?
* Bytes are the basic storage unit in
memory
* Each byte is stored at a specific
location in memory called an
address
* Each address has a unique
identifying number, like the seats
on an airplane
• Each address can hold only a
single byte
• Each address can be full or empty
seat C22
seat A22
seat B22
MEMORY
How is memory measured?
Size of memory is measured by the number of bytes available
• Kilobyte - 1,024 bytes
• Megabyte - about one million bytes
• Gigabyte - 1 billion bytes.
• Terabyte - 1 trillion bytes.
MEMORY
What are the two types of memory in the system unit?
1- Volatile Memory
 Loses its contents when the computer's power is turned off.
2- nonvolatile memory
 Types of memory that retain their contents when power is
turned off.
MEMORY
Types of Memory :
1- Random Access Memory (RAM).
2- Read Only Memory(ROM).
3- Flash Memory.
4- Virtual Memory.
5- BIOS.
6- CMOS.
1- Random Access Memory(RAM):
- Definition:
- It is our working memory storage, all the data which PC uses and
works with during operating are store here.
Why it is important?
Because it is the memory that your computer system uses to
store the data of all open programs and applications.
providing enough data from the hard disk for microprocessor to
use at any given time without making it wait.
1- Random Access Memory(RAM):
What is random access memory (RAM)?

Memory chips that can be read from and written to by the
processor and other devices

When the computer starts, operating system files are loaded
from a hard disk into RAM

As additional programs and data are requested, they also load
from storage into RAM

Most RAM is volatile
1- Random Access Memory(RAM):
RAM memory has two types:
1-Dynamic Random Access Memory (DRAM)
2-Static Random Access Memory (SRAM)
RAM Chips
10
2- Read Only Memory (ROM):
Definition:
Read Only Memory (ROM) is computer memory that can
permanently store data and applications within it.
ROM Types:
1- PROM (Programmable Read Only Memory ):
The data can be erase and rewrite on ROM.
2- EPROM (Erasable Programmable Read Only Memory) :
you can erase data and write on it more than one time.
3- EEPROM (Electrically Erasable Programmable Read Only
Memory ):
you can write without erase all data without special tool.
2- Read Only Memory (ROM):
What is read-only memory (ROM)?
- Memory chips that contain data, instructions, or information that
is recorded permanently
- Data can only be read, cannot be modified
- Nonvolatile — Contents not lost when the computer is turned
off
3- Flash Memory:
What is Flash Memory?
• Is a type of EEPROM
• Nonvolatile memory that can be erased electronically and
reprogrammed.
• Stores data and programs on many handheld computers and
devices such as Camera and mobile phone.
4- Virtual Memory:
- Because the processor speed so high compare with RAM
and hard disk , and computer try to have a good speed
for transfer data:
- There is a way to fetch unused space on HD and
determine small spaces that not used, and use it as
virtual memory.
- So , we have a new way to help RAM.
4- Virtual Memory(continue):
Practical:
From your computer determine virtual memory size.
To check the virtual memory:
- My computer –(Right click on a white space) properties
 advanced system sitting  Advanced options tab 
inside performance section click setting  from advanced
options tab  virtual memory.
(to change size use change).
Virtual Memory(practical):
Virtual Memory(practical):
Virtual Memory(practical):
Virtual Memory(practical):
5- BIOS:
What is it?
•
•
•
Basic Input Output System(BIOS):
Sequence of instructions the computer
follows to load the operating system and
other files when you first turn on the
computer.
Stored on ROM.
They are necessary to start the computer
 load the operating system
 and other files when you first turn on the computer
5- BIOS

The first software the computer runs is the one that inside these
encoded computer chips

When you turn on the computer, Power On Self Test or (POST)
ensure that all the basic input and output devices are working
probably. (how ?)

When power is turned on, POST (Power-On Self-Test) is the
diagnostic testing sequence that a computer's basic input/output
system (or "starting program") runs to determine if the computer
keyboard, random access memory, disk drives, and other hardware
are working correctly.
5- BIOS

If the necessary hardware is detected and found to be operating
properly, the computer begins to boot. If the hardware is not
detected or is found not to be operating properly, the BIOS issues
an error message which may be text on the display screen and/or
a series of coded beeps, depending on the nature of the problem.

This program builds by the company.
5- BIOS
6- CMOS:
A separate memory chip, called
Complementary
Metal-Oxide
Semiconductor (CMOS): chip stores the
information that describes specific device
parameters.
-
- CMOS does not store programs, only
data that is read by BIOS to be able to
talk to the changeable hardware.
6- CMOS:
-Stored as RAM .
-CMOS also acts as a clock to keep
date and time updated while the PC is off .
- CMOS chip is volatile (kept alive by battery). This way
the information contained in the CMOS are always
present even if the computer power is turned off.