Computer Fundamentals

1. Primary Memory
Primary memory is also known as main memory or may also refer to "Internal
memory." and primary storage. All those types of computer memories that are
directly accessed by the processor using data bus are called primary memory. That
allows a processor to access stores running programs and currently processed data
that stored in a memory location.
An example of Primary memory is RAM and ROM that store programs. These
memories are limited in capacity and manufactured by using integrated circuits (IC)
or semiconductor device. Its speed of Data accessing is faster than secondary
memory. It is more expensive than secondary memory.
When you turn on the computer, Generally CPU searches for essential codes in RAM
to get it. Otherwise, it goes to ROM. Yes, they both chips collectively called primary
memory in a computer system.
Types of Primary Memory
RAM (Random Access Memory)
The Word “RAM” stands for “random access memory” or may also refer to short-
term memory. It’s called “random” because you can read store data randomly at any
time and from any physical location. It is a temporal storage memory. RAM is
volatile that only retains all the data as long as the computer powered. It is the fastest
type of memory. RAM stores the currently processed data from the CPU and sends
them to the graphics unit.

2. There are generally two broad subcategories of RAM:
Static RAM: Static RAM is the form of RAM and made with flipflops and used for
primary storage are volatile. It retains data in latch as long as the computer powered.
SRAM is more expensive and consumes more power than DRAM. It used as Cache
Memory in a computer system. As technically, SRAM uses more transistors as
compared to DRAM. It is faster compared to DRAM due to the latching
arrangement, and they use 6 transistors per data bit as compared to DRAM, which
uses one transistor per bit. Its construction is comprised of two cross-coupled
inverters to store data (binary) similar to flip-flops and extra two transistors for
access control.
DRAM (Dynamic Random Access Memory) is also a type of RAM which is
constructed using capacitors and few transistors. The capacitor is used for storing
the data where bit value 1 signifies that the capacitor is charged and a bit value 0
means that capacitor is discharged.
Capacitor tends to discharge, which result in leaking of charges. The dynamic term
indicates that the charges are continuously leaking even in the presence of
continuous supplied power that is the reason it consumes more power.
To retain data for a long time, it needs to be repeatedly refreshed which requires
additional refresh circuitry. Due to leaking charge DRAM loses data even if power
is switched on. DRAM is available in the higher amount of capacity and is less
expensive. It requires only a single transistor for the single block of memory.
Key Differences Between SRAM and DRAM
1. SRAM is an on-chip memory whose access time is small while DRAM is
an off-chip memory which has a large access time. Therefore SRAM is faster
than DRAM.
2. DRAM is available in larger storage capacity while SRAM is of smaller size.
3. SRAM is expensive whereas DRAM is cheap.

3. 4. The cache memory is an application of SRAM. In contrast, DRAM is used
in main memory.
5. The construction of SRAM is complex due to the usage of a large number of
transistors. On the contrary, DRAM is simple to design and implement.
6. In SRAM a single block of memory requires six transistors whereas DRAM
needs just one transistor for a single block of memory.
7. DRAM is named as dynamic, because it uses capacitor which
produces leakage current due to the dielectric used inside the capacitor to
separate the conductive plates is not a perfect insulator hence require power
refresh circuitry. On the other hand, there is no issue of charge leakage in the
SRAM.
ROM (Read Only Memory)
ROM is the long-term internal memory. ROM is “Non-Volatile Memory” that
retains data without the flow of electricity. ROM is an essential chip with
permanently written data or programs. It is similar to the RAM that is accessed by
the CPU. ROM comes with pre-written by the computer manufacturer to hold the
instructions for booting-up the computer.
In a typical computer system, ROM is located on the motherboard. It contains the
basic instructions for what needs to happen when a computer is powered on. This is
typically referred to as the firmware of a computer. The firmware represents the
basic code to get the computer started. Once the computer is up and running, the
CPU takes over. Firmware is also referred to as BIOS, or basic input/output system.
On most modern computers, the read-only memory is located on a BIOS chip. The
BIOS chip is normally plugged into the motherboard.
ROM plays a critical part in booting up, or starting up, your computer. So, what
exactly happens?

4. When we press the power button, the BIOS chip wakes up and checks the various
components of our computer to make sure they are all present and functioning
properly. This is why it's called firmware as opposed to software; the set of
instructions on the read-only memory interact directly with the various hardware
components.
RAM Vs ROM
RAM
Acronym of RAM: Random Access Memory
Definition of RAM: The Read and Write memory (R/W memory) of a computer is
called a RAM. It is called random access since any memory location can be accessed
in a random manner for reading and writing.
Use of RAM: The user can write information into RAM and read information from
it.
RAM Volatility: It is a volatile memory. It usually refers to “temporary” memory.
Which means that when the system is shutdown, the memory is lost.
Speed of RAM: High-speed memory with fast access time.
Data: Data can be modified any number of times.
Storage Capacity of RAM: Store multiple gigabytes of data, vary from 1GB to
256GB per chip.
RAM Costing: It is much expensive compared to ROM.
RAM Types: There are two important types of RAM:-
 SRAM (Static RAM)
 DRAM (Dynamic RAM)
RAM Examples: Ram in Computer, Phones, Laptops, Tablets, Gaming machine.
Acronym of ROM: Read Only Memory
Definition of ROM: It is a computer memory which stores information that can only
be read, modifying it is either impossible or very difficult.

5. Use of ROM: The information from ROM can only be Read and it is not possible
to Write fresh information to it. ROM is used for storing a special set of instructions,
which the computer needs when it starts up(boots up).
ROM Volatility: It is a non-volatile memory. The information stored in it is not lost
even if the power supply goes off. Thus, the information is stored permanently.
Speed of ROM: It has slow access time in comparison with RAM.
Data: Data can be modified to a limited number of times.
Storage Capacity of ROM: Store several megabytes of data, commonly 4MB or 8
MB per chip.
ROM Costing: It is much cheaper compared to RAM.
ROM Types: There are three types of ROM:-
 PROM (Programmable ROM)
 EPROM (Erasable Programmable ROM)
 EEPROM (Electrically Erasable Programmable ROM)
ROM Examples: Computer BIOS(Basic Input/Output System)
Read Only Memory ROM is divided into four types:
(1) Programmable ROM: a memory chip on which the write operation of data can
be performed only once. The data is stored on this chip permanently. That is once a
program is written on the PROM, it cannot be erased or destroyed. To write the data
on the PROM chip, a device known as PROM programmer or PROM burner is
required. The method of writing data on the chip is known as burning the PROM.
PROM is reliable and stores the data permanently without making any change in it.
It is mostly used in video games and electronic dictionaries.
(2) Erasable PROM: a type of ROM in which data can be erased or destroyed using
Ultraviolet Light. Erasable ROM provides the facility of changing the contents of
the data.
(3) Electrically Erasable PROM: a type of ROM in which data can be erased or
destroyed by exposing it to an electric charge. It has the ability to retain the data in
it, even if the power of the computer system is switched off. In this type of memory,
the data can be written or erased only one byte at a time because of which it works
very slowly.

6. (4) Flash ROM: a type of EEPROM that stores the information using floating-gate
transistors, which can store electric charge for a longer period of time as compared
to the normal transistors. This memory is mainly used in the memory cards of mobile
phones, digital cameras and ipods for storing data. The data stored in flash ROM
memory can be easily transferred using transmission mediums such as data cable,
Bluetooth and infrared technology. Flash ROM has faster speed of reading data, as
compared to any other type of ROM.