What is Memory Organization of a Computer System?

1. Assignment of “Computer Architecture and Organization”
Title: What is Memory Organization of a Computer System?
Writter: Taminul Islam | ID: 181-15-11116
Student, Department of CSE
Submitted to: Professor Dr. Md. Fokhray Hossain
Associate Dean & Professor, Department of CSE
Daffodil International University

2. What is Memory Organization of a Computer
System?
Taminul Islam, ID: 181-15-11116
Department of CSE, DIU
*Assignment delivered to
Professor Dr. Md. Fokhray Hossain
Associate Dean & Professor, Department of CSE
Daffodil International University
Introduction
A memory unit is the collection of storage units or devices together. The memory unit stores the binary
information in the form of bits. It is used for storing programs and data that are required to perform a
specific task. For CPU to operate at its maximum speed, it required an uninterrupted and high speed
access to these memories that contain programs and data. Some of the criteria need to be taken into
consideration while deciding which memory is to be used:
 Cost
 Speed
 Memory Access Time
 Data Transfer Rate
 Reliability
Description
Basically Memory or Storage is classified into two categories:
 Volatile:
Volatile memory is computer storage that only maintains its data while the device is powered. It
contrasts with non-volatile memory, which does not lose content when power is lost. Non-
volatile memory has a continuous source of power and does not need to have its memory content
periodically refreshed. Example: RAM
 Non-Volatile:
Non-volatile memory is a type of computer memory that has the capability to hold saved data
even if the power is turned off. Unlike volatile memory, it does not require its memory data to be
periodically refreshed. It is commonly used for secondary storage or long-term consistent storage.
It is widely used in memory chips for USB memory sticks and digital cameras. Non-volatile
memory eradicates the need for relatively slow types of secondary storage systems, including
hard disks. Example: Optical Disk, ROM

3. Memory Hierarchy:
A computer system contains various types of memories like auxiliary memory, cache memory, and main
memory. Main memory is also called as Primary Memory. There are also Register Memory. The total
memory capacity of a computer can be visualized by hierarchy of components. The memory hierarchy
system consists of all storage devices contained in a computer system from the slow Auxiliary Memory
to fast Main Memory and to smaller Cache memory.
Auxiliary Memory:
The auxiliary memory is at the bottom and is not connected with the CPU directly. However, being slow,
it is present in large volume in the system due to its low pricing. This memory is basically used for
storing the programs that are not needed in the main memory. This helps in freeing the main memory
which can be utilized by other programs that needs main memory. The main function of this memory is
to provide parallel searching that can be used for performing a search on an entire word. For
example: Magnetic disks and tapes are commonly used auxiliary devices. Other devices used as auxiliary
memory are magnetic drums, magnetic bubble memory and optical disks.
Primary Memory / Main Memory:
The main memory is at the second level of the hierarchy. Due to its direct connection with the CPU, it is
also known as central memory. The main memory holds the data and the programs that are needed by the
CPU. The main memory mainly consists of RAM, which is available in static and dynamic mode. Main
memory is made up of RAM and ROM, with RAM integrated circuit chips holing the major share.
 RAM (Random Access Memory):
Random access memory (RAM) is the best known form of computer memory. RAM is
considered "random access" because you can access any memory cell directly if you know the
row and column that intersect at that cell. Types of RAM –
 Static RAM (SRAM)
– A bit of data is stored using the state of a flip-flop.
– Retains value indefinitely, as long as it is kept powered.
– Mostly uses to create cache memory of CPU.
– Faster and more expensive than DRAM.
 Dynamic RAM (DRAM)

4. – Each cell stores bit with a capacitor and transistor.
– Large storage capacity
– Needs to be refreshed frequently.
– Used to create main memory.
– Slower and cheaper than SRAM.
 ROM (Read Only Memory):
ROM is used for storing programs that are Permanently resident in the computer and for tables of
constants that do not change in value once the production of the computer is completed. The
ROM portion of main memory is needed for storing an initial program called bootstrap loader,
witch is to start the computer software operating when power is turned on.
There are five basic ROM types:
1. ROM - Read Only Memory
2. PROM - Programmable Read Only Memory
3. EPROM - Erasable Programmable Read Only Memory
4. EEPROM - Electrically Erasable Programmable Read Only Memory
5. Flash EEPROM memory
Cache Memory:
Cache memory is at the top level of the memory hierarchy. This is a high speed memory used to increase
the speed of processing by making current programs and data available to the CPU at a rapid rate. Cache
memory is usually placed between the CPU and the main memory.
The main memory occupies the central position because it is equipped to communicate directly with the
CPU and with auxiliary memory devices through Input/output processor (I/O).
When the program not residing in main memory is needed by the CPU, they are brought in from
auxiliary memory. Programs not currently needed in main memory are transferred into auxiliary memory
to provide space in main memory for other programs that are currently in use.

5. The cache memory is used to store program data which is currently being executed in the CPU.
Approximate access time ratio between cache memory and main memory is about 1 to 7~10.
Hit Ratio:
When the CPU refers to memory and finds the word in cache, it is said to produce a hit. Otherwise, it is a
miss. The performance of cache memory is frequently measured in terms of a quantity called hit ratio
Hit ratio = hit / (hit+miss).
Conclution
From this study we will learn about the total memory organization of a computer system. We will know
from this study how the memory or storage will work in between other components of a computer
system. How the storage have designed in the computer it will also showed in this study. We will know
about the processor, CPU lightly. About the main memory, auxiliary memory, RAM, ROM, cache
memory and register memory also discussed here.The defination and working process including proper
examples also can be learn from this study.
References:
[1] https://www.studytonight.com/computer-architecture/memory-organization (Abhishek Ahlawat,
2020)
[2] https://whatis.techtarget.com/definition/volatile-memory (Margaret Rouse, August, 2014)
[3] https://www.techopedia.com/definition/2793/non-volatile-memory-nvm (February, 2017)
[4] http://www.sdcmsmzn.com/notes/mohit/MemoryOrganization.pdf (Mohit. May, 2020)