Table of Contents 

 1 What is RAM?
 2 Architecture of RAM
 3 Read and Write Operations
 4 Types of RAM
 5 Advantages of having RAM
 6 Disadvantages of RAM:
 7 What is ROM?
 8 Types of ROM
 9 Advantages of ROM
 10 Disadvantages of ROM: (with most use cases of ROM)
 11 Summary and Facts
 12 References:

Systems require storage units whether it was for short term or long term purposes.
Computer systems take advantage of the memory systems they have, whether it was
Random Access Memory (RAM), Read-Only Access Memory (ROM), or highly dense
storage units like hard drives.

You might be thinking why we can’t have one storage unit for all. To put it simply, it’s
because each system is specially designed to work efficiently for its function rather
than carry out all the functions you desire.

Let’s take this article as an example of how you can be utilising those three storage
compartments on your computer right now.

We’ll start from the beginning with Read Only Memory (ROM). Without ROM you
couldn’t initiate your system to boot up, this is because ROM is where the firmware is
placed by the manufacturer i.e. your systems instructions this can also be referred to
as BIOS.

To open up this article you had to initiate a sequence of commands, one of them is
opening up a browser. For this to happen, the computer system will have to make use
of its short term memory, this is referred to as Random Access Memory (RAM). Despite
it being for a number of seconds, sometimes even instantly depending on your
computer specification, the loading time between clicking on a program and getting
an interface that a user can see and use is the time your system is sending and
receiving information from the RAM.
Lastly, once you complete reading this article, you might want to save it. When you
press the save button, the article is saved into your hard drive, which is used for long
term storage, moreover, this is because if goes to the RAM, and you shut down your
computer, you will not see it when you reboot your computer. This is why RAM is
considered to be volatile, as it’s only considered to be temporary storage for tasks and
functions you require which can be modified, unlike ROM.

Computer architects are always trying to increase efficiency in our computer systems
and how we store our content. Nowadays, the use of cloud computing is emerging,
where you physically store your content on a server in various locations around the
world, and they are accessible from the internet.

Though there are concerns over cloud computing such as data security, the longevity
of a company (this rises bankruptcy issues as you pay for your services for cloud
computing), and accessibility where the performance depends on how much a
customer is willing to pay for WAN bandwidth.

What is RAM?
RAM = Random Access Memory

The earliest form of RAM dates back to the 1940s which is when the first computers
emerged. Magnetic memory had relied on magnetised rings to store data in each ring.
This incorporated very large installations as each ring was wired separated, and each
one of these rings managed to store a “bit” of data, the direction of magnetisation
indicated one or zero (binary form).

The penultimate breakthrough in computational memory came in around the 1970s

with the innovation of solid state memory within integrated circuits.

These memory units had used very small transistors, allowing architects to build
memory units that can withhold lots of information in a small amount of space.

Essentially, RAM is the computer system short term memory, which is the opposite of
what your hard drive is (SSD). RAM is also considered to be “volatile” as it’s only used
for temporary storage, meaning that the content will not be available if the system is
shut down and rebooted.
RAM will temporarily store everything that is running on the system, whether if you are
using a text editor, browser (cached), or an image editing tool.

The benefit of having RAM in a computer is that the CPU can fetch the information it
requires rapidly rather than excavate through the solid state hard drive (SSD). Despite
have SSD’s which are a lot faster nowadays, they are still much slower than RAM.

Architecture of RAM
Due to RAM architecture, the memory cells can be accessed for information from
anywhere on the computer system.

This communication between different peripherals and RAM is achieved by data input
and output lines, control lines which specify the direction of transfer, and address
selection lines.

(A “word” is a unit that a machine uses when working with memory, i.e. 32bit machine,
means the word is 32bits long)
(A “bit” is the basic unit of information in computing)
Read and Write Operations
RAM can perform two operations, they are read and write.
Read: A signal transferring out
Write: A signal transferring in
Once the RAM accepts one of these control units, the internal circuits, which are
situated inside the memory, provide the function, which is expected, from the user.

The process is:

1. The binary address of the required word is applied into the address lines
2. Apply the “data bits” that will be stored in memory into the data input
lines
3. The write input will be activated
4. Once the steps above are complete, the memory unit will take the bits in
the input data lines and will store them, specified by the address lines.
To transfer a stored word out of the memory unit the following occurs:
1. The binary address of the required word is applied into the address lines
2. Activate the read input (content of the word does not change after
reading)
Lastly, the memory unit will take the “bits” from the “word” which was selected by the
address, and apply them into the output data lines.

Types of RAM
Although there are quite a few types of RAM we will focus on the main three:

SRAM (Static Random Access Memory)

SRAM is a type of memory, which uses multiple transistors, usually around four to six.
There is no capacitor (they act like batteries, they store electrical energy) in each cell
and SRAM is used for caching.

Advantages include:
 Simplicity
  Performance
 Reliability
 Low idle power consumption
Disadvantages include:
 Density
 Price
 High operational power consumption
DRAM (Dynamic Random Access Memory)
The memory cells in this type of memory are paired with a transistor and a capacitor
requiring constant refreshing.

Though it is more complicated than SRAM due to its complicated circuitry and timing
requirements. The advantage of using DRAM is because of its memory cell structural
simplicity. These units only require one capacitor and transistor per bit, compared to
SRAM which requires 4-6. This makes DRAM less costly per bit.

VRAM (Video Random Access Memory)

This type of memory also known as “Multiport Dynamic Random Access Memory”
(MPDRAM), is specially used for 3-D accelerators or video adapters.

The reason why it is also called “multiport” is that VRAM has two independent access
ports instead of one. This allows the graphics processor and the CPU to access the
memory unit simultaneously.

Resolution and colour depth is determined by the VRAM specifications on a device,

furthermore, VRAM also holds graphic specific information like 3-D cemetery data and
texture maps.

Most systems nowadays use SGRAM (synchronous graphics RAM), as it’s less costly
and the performance is nearly the same.

Advantages of having RAM

 Increases the computer system speed, essentially, the more RAM a
system has the faster it will operate.
 RAM is a component that is a mandatory to have in a system to allow for
the storage of data, which will be processed by the CPU.
 It’s efficient. It’s extremely fast compared to hard drive storage for a CPU
to read data from.
  It can write and read operations.
 RAM is power efficient.
 Cost less than SSD’s and operate faster than them.
Disadvantages of RAM:
 If CPU wants to read data only from the RAM, then the data access from
the cache and the registers is slow in comparison to ROM.
 RAM is volatile, which means it is difficult to store data for a lengthy
period of time. Unplanned circumstances like a power outage can result
in data loss.
 It is expensive.
What is ROM?
ROM = “Read Only Memory”

ROM is a non-volatile read only storage unit within electronic systems, however, with
ROM, data that is stored inside the memory units cannot be electrically modified after
the device has been manufactured, as it is hard wired. 

ROM is a type of memory, which is useful at storing information, which doesn’t change
during its lifespan in the system, this is referred to as firmware.

Read only memory is memory, which is hard-wired, this can include a diode matrix, for
instance, a system that cannot be electronically changed.

Architecture of ROM:

Information in the form of binary is stored permanently inside ROM by the

manufacture, the information is injected in the form of bits. ROM consists of logic
gates only, arranged in a way that they store specified bits.
Block structure:
 The unit consists of k input lines and n out lines.
 The k input lines take the input address from where we want to access
the content of the ROM.
 Since the input lines are either 0 or 1 (binary form). The input lines can be
referred to as 2k total addresses and each of these addresses contains n
bit of information, which will be given out as the output of the ROM. This
is specified as 2k x n ROM
Internal structure:
The internal structure consists of two components: the decoder and OR (logic) gates.

 The decoder is a combinational circuit. It is used to decode any encoded

form like binary to understandable forms like decimal form. Within the
ROM structure, the input into a decoder will be binary and the output will
be represented in decimal form.
 All the OR logic gates will have outputs of the decoder as their input.
Types of ROM
ROM can be classified into the following:

MROM (Masked Read Only Memory)

 MROM is the original type of ROM, it is read only. Therefore this memory
unit cannot be modified.
PROM (Programmable Read Only Memory):
 This type of ROM is one, which can be programmed once the chip has
been created. However once the chip has been programmed, the
information written is permanent and it cannot be erased or removed.
EPROM (Erasable Programmable Read Only Memory):
 This type of memory, which was developed in 1971 by Dov Frohman, can
be reprogrammed only when exposed to ultraviolet light, otherwise it
cannot be modified and therefore no new data can be saved. These types
of chips are not commonly used anymore in computer systems, and their
use has been replaced by EEPROM chips.
EEPROM (Electrically Erasable Programmable Read Only Memory) :
 This type of memory can be erased and reprogrammed only by using an
electrical charge. EEPROM was developed in 1970 by George Perlegos
when he was in Intel. The edge that EEPROM has, is that it can remember
data when the system is powered off. EEPROM is considered to be more
superior to PROM and EPROM. It is used for the BIOS (Basic input/output
 system which deals with hardware initialisation during the booting
process) of computers designed after 1994.
 The use of EEPROM allows the computer system to update the BIOS
without the need to open the computer system or remove any chips.
Advantages of ROM
 It is non-volatile, meaning data which was set by the manufacture will
function as expected when device is turned on.
 Due to them being static, they don’t need a refreshing time.
 In comparison to RAM, the circuitry is simpler.
 Data can be stored permanently.
Disadvantages of ROM: (with most use cases of ROM)
 ROM is a read only memory unit, so it can’t be modified.
 If any changes are required, it’s not possible.
Summary and Facts
What is RAM?
Random Access Memory (RAM), is one of the most vital components of a computerised
system, whether it was mobile phones, gaming consoles, smart phones etc. Without
RAM, these devices will not be able to function at all, and if they can function it will be
at a much slower rate, that what the user visualises will be a slideshow rather than a
constant flow.

Types of RAM
 SRAM: Static Random Access Memory
 DRAM: Dynamic Random Access Memory
 VRAM: Video Random Access Memory
What is ROM?
ROM is a non-volatile read only storage unit within electronic systems, with ROM, data
that is stored inside the memory units cannot be electrically modified after the device
has been manufactured, as it is hard wired, and an example of ROM is firmware.  

Nowadays, ROM is essential for the devices that we use in our everyday life. While ROM
was made as a Read only memory unit, some of them have been modified to allow
users to make adjustments to suit their own preferences.

ROM is used in many appliances, such as microwaves, dishwashers, electrical grills,

and smartphones, in essence, any device which needs to know how to work when it’s
turned on, after being turned off.
Types of ROM
RAM ROM

Random Access Memory Read Only Memory

Volatile memory Non volatile memory

If the system is turned off, the information it carries will st

If the system is turned off, the information will
be on the memory, meaning that the system can retrieve i
be deleted
again when the system is switched on

Requires power to store data Doesn’t require power to store data

ROM is used to store BIOS/Firmware/software, programs a

RAM is a temporary storage unit to store files
instructions which don’t change

Chips often range from 1 to 256 GB Chips often range from 4 to 8 MB

Available in two primary sizes They can vary in size

Temporary memory Permanent memory

 MROM (Masked Read Only Memory)
 PROM (Programmable Read Only Memory)
 EPROM (Erasable Programmable Read Only Memory)
 EEPROM (Electrically Erasable Programmable Read Only Memory)
Advantages of RAM
The advantage of RAM in a system is essentially its speed, the more RAM a system has
the faster the system will operate, this increases the system efficiency. Although SSD
hard drives are quite fast nowadays, they’re still considerably slower than RAM.

Disadvantages of RAM
Despite RAM being less costly than SSD hard drives, they are still relatively expensive.
RAM’s biggest downside is considered to be the fact that they are volatile, which
means that it can’t store data after the system is shut down.

Advantages of ROM
The advantage of ROM is that it’s non volatile, which means data can be stored
permanently, and they don’t require a refreshing time as they are static. This enables
the circuitry of the element to be simple in comparison to RAM.

Disadvantages of ROM: (with most use cases of ROM)

A massive disadvantage of ROM is that it’s a read only unit, so this means that
programmers cannot modify it, if any changes were required.

RAM vs. ROM

References:
1. https://www.digitaltrends.com/computing/what-is-ram/
2. https://centralvalleycomputerparts.com/articles/-ram-explained/
3. https://www.studytonight.com/computer-architecture/random-access-
memory
4. https://computer.howstuffworks.com/ram2.htm
5. https://uk.crucial.com/articles/about-memory/different-types-of-
memory-explained
6. https://www.computerhope.com/issues/ch001361.htm
7. https://tijeii.wordpress.com/2017/02/17/characteristics-advantages-
disadvantages-of-ram-memory/
8. https://t4tutorials.com/ram-types-of-ram-advantages-of-ram-
shortcomings-of-ram/
9. https://am7s.com/what-is-rom/
10. https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-536.html
11. https://en.wikipedia.org/wiki/Dynamic_random-access_memory
12. https://tijeii.wordpress.com/2017/10/26/disadvantages-of-read-only-
memory-rom/
13. https://www.classmate4u.com/ram-and-rom/