Types of primary memory (RAM, ROM, Cache)

In a computer system memory is a physical device, that is used to store, retain, acquire and retrieve data and information. Primary memory used to store data only in a execution time.

The memory device contains different cells, every cell contains a unique location. Data and information are stored in these unique locations.

It stores all types of data like raw data (given input by the user), intermediate results and final results are stored in memory. It may be or may not be store data permanently. There are mainly 2 types of primary memory. However, if we considered Cache Memory, it is of 3 types.

Primary-memory
Primary memory

RAM > Random Access Memory

RAM
RAM

RAM (Random Access Memory), contains one or multiple memory modules that store data temporarily.

It is also called volatile memory because data get erased when the computer is turned off. It holds data and instruction frequently during processing. When we are launching the software, then it is loaded into RAM.

Why it is called RAM?

  • It randomly select any location of memory to store and retrieve data.

What is RAM used for?

  • Random Access Memory (RAM) is the most important component in the computer system, for determining a system’s performance. It gives uses a place to store and retrieve data on short-term basis.

Types of Random Access Memory (RAM)

DRAM

DRAM stands for Dynamic RAM, It is the most important part of RAM used in computers. It has a better performance and is a more energy-efficient memory unit. It consist of a transistor and capacitor.

There is a faster dual data rate(DDR) in DRAM. New versions of DDR are DDR2, DDR3, and DDR4. New versions are of better performance and more energy-efficient than.

SRAM

It stands for Static RAM, It is also one common type of RAM used in a computer system. It bigger in size and is costly having six transistors in each cell.

It is only used for data cache within a CPU itself or as RAM in the high-speed server system.

It is a semiconductor memory, highly used in electronics, microprocessors, and others using computing for general purposes. This type of memory gains its name from the fact that data is held statically.

While the data in the SRAM memory does not need to be refreshed dynamically, it is still volatile, meaning that when the power is removed from the memory device, the data is not held, and will disappear.

Difference between SRAM and DRAM

RAM DRAM
It Stands for Static RAM. It stands for dynamic RAM.
Does not require a refreshing circuit. The refreshing circuit is needed.
It loses data or instruction when the computer is turned off.
It stores voltage as a bit. It stores bit as the charge.
It is more expensive. It is cheaper in cost.
SRAM uses transistors and latches. DRAM uses capacitors and very few transistors.
It is widely used on the processor or kept between the main memory and processor The DRAM is placed on the motherboard.
SRAM is of a smaller size. (e.g. 1 MB to 16 MB) DRAM is available in a larger storage capacity. ( e.g. 1GB to 16 GB)
SRAM has lower access time, which is faster compared to DRAM. DRAM has a higher access time. It is slower than SRAM.

ROM > Read Only Memory

ROM is a primary memory. It stores some standard processing programs to operate the PC. Processers only read the content of ROM but cannot change the content.

ROM
ROM

It is also called a flash memory chip, that contains a small amount of memory which may be permanent or semi-permanent data.

Types of Read-Only Memory (ROM):

PROM

It stands for programmable read-only memory. In this memory, data can be written only once and will remain there forever.

It can retain its content when the computer is turned off. PROM is manufactured in an empty state and then programmed later using PROM Programmer or burner. 

EPROM

It stands for Erasable programmable read-only memory, In this memory can be erased by exposing it to ultraviolet light. Ultraviolet light clears its contents, marking it possible to reprogrammed memory.

EEPROM

It stands for Electrically erasable programmable read-only memory, Same as EPROM but it erases content by exposing it to electrical charge and then can be reprogrammed.

It retains its content when the power is turned off. It is like flash memory. However, It requires data to be written and erased one byte at a time. This makes it faster than flash memory. 

Difference between RAM and ROM

RAM ROM
RAM is a volatile memory. ROM is a non-volatile memory because it can retain data.
Data stored can be retrieved and altered. Stored data can only be read.
RAM is used to store data that the CPU needs for current instruction processing. It stores the instructions required during the bootstrap of the computer system.   
It is a high-speed memory. It is much slower in comparison to RAM
The CPU can access the data stored on it. The CPU can not access the data.  
Higher capacity with large size. Less capacity with Small size.  
The data stored is easily accessible. The data stored is not as easily accessible. 
RAM is used as CPU Cache, Primary Memory. ROM is used as firmware by microcontrollers.

Cache Memory

Cache memory is the fastest memory type that is kept between RAM and CPU. It holds addresses of all the frequently requested data and instructions, which can be available immediately when needed to the CPU.

Cache-Memory
Cache Memory

It is used to hold those part of data and program which are most frequently used by the CPU. Cache is divide into three parts (L1, L2, and L3) depending upon system architecture.

 Cache has a high-speed storage area that is used during reading and writing processes from the disk.                              

Buffer Memory

Buffer memory is used to adjust the difference in speed between two processes/devices that exchange or use data.

Buffer is a normal storage area on RAM for temporary storage. It is mostly used for input/output instructions. It works in these areas (RAM) where the CPU can store data temporarily. It can be part of the primary memory or some other area like a hard disk.

buffer memory
buffer memory

Difference between Buffer and Cache

  Buffer Cache
Buffer is used to adjusting the difference in speed between two processes that exchange or use data. A cache is a smaller and fastest memory component in the computer which can hold the address of the frequently running programs.
It is used for input/output processes.
It is used during reading and writing processes from the disk in a computer system.
It is a normal storage area on ram for temporary storage. It is a high-speed storage area for temporary storage.
It is made from DRAM. It is made from SRAM.
It does not increase accessing time. It increases the accessing speed of the CPU.

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by Janak Saud
Author of Informer Guru, IT Student

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