Computer Memory, Primary and Secondary Memory and their types fully explained

Computer Memory:

Computer Memory- In this article we will be looking at different types of the computer memories “Primary and Secondary Memories”. We will also study about RAM, DRAM, SRAM, ROM, PROM, EPROM, EEPROM, UV EEPROM, Cache memory, Hard disk, CD/DVD drive, Pen Drive, and Blue-ray Disc.


Memory is one of the essential and important parts of the computer. We cannot say that there is only one type of memory in our system that is working. There are layers of memory available in the computer that can make together and increase the performance of the computer. So what are different types of memories? What are the uses of those memories and how they work collectively? We will discuss this in our article.

Computer memory is divided in to two types:

  • Primary memory
  • Secondary memory

Primary memory:

Primary memory is that type of memory which directly communicates with the processor. The primary memory is father divided into two types:

  • Cache memory
  • Main memory

Types of Primary memory:

As you know primary memory is very expensive so technologies have been developed so that we can have different types of memory which can be optimized. The primary memory or main memory is of two types:

  • RAM
  • ROM

RAM is random access memory which is also known as the main memory of the computer. This is volatile memory. The RAM memory data cannot be retrieving. This is the broad type of primary memory as you can see here random access memory which is the RAM the read-only memory. When the computer is powered off the data store in the RAM is lost therefore is called volatile memory. The RAM is made up of semiconductor and flip flop. The Random access memory is again of two types:

  • DRAM which is the dynamic Ram
  • SRAM which is the static Ram

In DRAM each memory cell is made of one transistor and one capacitor what does that mean that means that the cell starts losing it charge the moment the data is stored there so we have to keep passing the charge and refreshing the memory. We have to keep refreshing it so that that data value is stored there till it is deleted. So it needs to be refreshed 1000 times per second however it can have large number of cells. So primary memory of most of the PCs is made of DRAM is dynamic Ram because we can have large amount of data. The DRAM store data for long period of time.

computer memory

Static RAM:

What happens in static now static Ram each cell is made of just one flip-flop where you store a bit 0 or one and it will remain there until the power supply is o. It does not need to be refreshed however that means that it is used only in specialized applications. It is more expensive than the dynamic Ram. We know that computer work on binary language. So whatever the input the computer will convert it in to binary form. Similarly the output generated by the computer will also be in binary form which is then converted in to human understandable language. In SRAM we have six transistors the two transistors among the six transistors are the path transistors which provides path for the bit lines. The four transistors are two crossed coupled inverters among which T1 and T2 is CMOS inverter pair and T3 and T4 is another CMOS pair.

computer memory


ROM the read-only memory it can be read only by the processor. Data to be stored is written during the manufacturing phase only. This is permanent memory because it can remain in the computer even when the computer is off. The manufacturers who are manufacturing the ROM will put whatever data, instructions and programs are to be put in while manufacturing. Once it is installed in any system it is put on any processor. The system cannot write anything on it or make any changes. So it contains data that does not need to be altered for example logarithmic tables. The logarithmic tables will always remain the same so they can be put into the ROM if the system needs to access it again and again. ROM is slower and hence cheaper than RAM. So technologies are now available so that we can program these ROMs.

Read only memory ROM is again of two types:

  • PROM

PROM is programmable ROM and EPROM is erasable programmable ROM. EPROM which is again of two types:


We will look at these in detail Ram as I told you earlier it stands for random access memory it is the processor accesses all memory addresses directly for a ram. It is available in very small quantities why because it is very expensive but still that quantity is up to 1 gigabit or too big a bit it is volatile but it may be off these two types DRAM and SRAM.


The first is programmable ROM. It can be programmed using a special hardware device called the PROM burner using the PROM burner you can edit it you can add a new program to it.

EPROM (Erasable programmable ROM):

In the PROM whatever is written you can add to it you cannot erase anything in the case of erasable PROM you can erase what is existing and write something new this erasing can be done by electrical signals or UV signals so there are two types:


Cache memory:

Now let’s look at the most special type of memory which is the cache memory. It is a small piece of high speed volatile memory available to the processor for fast processing. When the processor needs to do various fast processing and it has run out of RAM then the cache memory is made available to it may be a reserved portion of the main memory.

Cache memory is very fast and contains data for small interval of time because its size is small. Cache memory is path between the RAM and processor. It is in form of resistor. Another chip on the CPU or an independent high speed storage device this is used only in special cases where very high speeds are required it is made of fast speed static Rams because the static Rams are being used. They don’t need to be refreshed so the data can be accessed quickly process of keeping some data and instructions in cache memory for faster access is called caching so if you are keeping some data or the instructions in cache memory that is for caching whenever the processor needs any piece of data or instruction. It will check the first cache once it checks the cache memory and it is not available then it will go to other part of the RAM and check whether it is available finding data or instruction in the cache memory is called a cache hit.

Secondary memories:

The secondary memory is external memory. The speed of the secondary memory is slower than primary memory. But the storage capacity of the secondary memory is more than the primary memory. The secondary memory can be upgraded according to our requirement.

Secondary memory could be:

Fixed device:

  • Hard disk
  • CD / DVD drive

Removable device:

  • Pen drive
  • blu ray disc

Hard disk:

Hard disk was introduced by IBM in 1980s. Hard drive is made of circular magnetic disks which are around a spindle. It is made up of a series of circular disks called platters which are arranged one over the other half inch apart around the spindle a central column. It is made of non-magnetic material like aluminium alloy or coated with 10 to 20 nano meter of magnetic material.

computer memory

The standard diameter of each disk is 40 inches it can rotate with speeds vary from 4200 rpm to 15,000 rpm because some computers need very high speeds like force file servers or any other server that a network is having so then we will use the 15,000 rpm hard disks. The data is stored by magnetizing or demagnetizing the magnetic coating. a magnetic ray is passed and then it will be stored as one otherwise it will be removed and that will be a 0. A magnetic reader arm is used to read data to and from the hard disk. A typical modern hard disk drive has capacity in terabytes. so this was all about the hard disk drive.

Floppy disk drive:

Floppy disk drive is very small in size and it is made up of plastic on which consist of magnetic material layer. Floppy disk size is of 1.4 MB and its speed was 360 rpm.

Optical disk:

The optical disk is polycarbonate circular disk which consists of chemical layer. It stores the data in the digital form. For the data read and write low level efficiency of laser will be used.

CD drive:

The CD drive CD it stands for compact discs they are circular discs that use optical rings if you remember magnetic rays were being used for hard disks. here optical rays are used to read and write they are very cheap you can get 700 MB of storage space for less than a dollar. CDs are inserted in the CD drive that is built into the CPU cabinet and they can then be taken out and used in some other system. So they are portable. There are many types of CDs let’s look at them:

CD-ROM read only memory as you already know read only means that once something has been written it can only be read it cannot be changed from pack. This recordable some data has been written there already but then you can also add something to it so that is CD-R CD recordable. The third is CD rewritable so you can erase the data and then write a new piece of information there that would be CD-RW.


Now let’s look at the DVD drive what is a DVD drive digital video display drive they are optical devices that store 15 times as much as data as can be stored on a CD so that is why they are used to store rich multimedia files or do video you know you can store movies complete movies in fact more than one or two movies on a single DVD. They come again in three varieties read-only recordable and rewritable like for a CD.

Pen drive:

Let’s look at the pen drive it is a portable memory device that uses solid-state memory rather than magnetic fields or lasers hard-disk we’re using magnetic fields CDs and DVDs. We are using optical rays but the pen drive uses solid-state memory what does that mean that means that it uses semiconductor chips inside it. It uses a technology similar to RAM because RAM is also made up of silicon chips. it is non-volatile again and it is also called USB Drive, K drive or flash memory. Why it is called a USB Drive because it goes into the USB port of your CPU.

Blu-ray disc:

It is an optical storage media that is used to store high-definition video and multimedia files. It uses shorter wavelength lasers as compared to CDs and DVDs that means it is again using optical Ray’s to store data because it uses shorter wavelength optical Ray’s that means more and more data can be written into the same amount of space so this enables writing arm to focus more tightly on the disc and hands back in more data more data as compared to CDs and DVDs it can usually store up to 128 GB of data so this was all about different types of secondary memory devices that we can use to store our data instructions.

Engr Fahad

My name is Shahzada Fahad and I am an Electrical Engineer. I have been doing Job in UAE as a site engineer in an Electrical Construction Company. Currently, I am running my own YouTube channel "Electronic Clinic", and managing this Website. My Hobbies are * Watching Movies * Music * Martial Arts * Photography * Travelling * Make Sketches and so on...

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