A pen drive, which is often known as a memory stick or USB stick, is a portable electronic device that is used to store different types of data such as photos, videos, music files, and other graphics documents. It can be easily carried to any place due to its compact size. The data from the pen drives can be easily assessed by attaching it to the USB ports provided on the computer’s motherboards or mobile phones. Due to its ability to store a huge amount of data and that too with high data transfer speed, it has easily replaced the old data storing devices such as floppy disks, digital versatile discs (DVDs)and compact disks (CDs). The data storage capacity of the pen drives usually ranges from 2 GB to 128 GB, but the latest designed pen drives are also available in a few range of TBs. The weight of the standard pen drive is around 30 grams. The invention of pen drives has saved a lot of time as one need not waste the time on burning the CDs and finding the floppy disk labels to save or access the data. One can easily access or share the data by just plugging in the pen drive with the device. In this article, we’ll focus on the physics behind the working of the pen drive.
Components of Pen Drive
The pen drive comprises a small printed circuit board (PCB), which is usually built of plastic or metallic body. This device used the technology of EPROM, i.e., Erasable Programmable Read-only Memory, which means the data stored in the pen drives can be read, written, and erased easily. The PCB is provided with a power circuit, integrated circuits, and USB connectors. One of the integrated circuits acts as the interface between the USB connectors and the memory, and another integrated circuit is a NAND flash memory, which stores all the data. The data stored in the pen drive is controlled by a 12MHz clock signal crystal oscillator.
The following image shows the internal structure of the pen drive.
Main Components of Pen Drive
1. USB Connector
The USB connector is the interface between the computer (where the pen drive is attached) and the NAND flash memory chip. It is secured by a removable cap. Mostly, the pen drives consist of a standard type-A USB connection that is connected to the port of the device, but nowadays, a faster version, i.e., USB Type-C connector is gaining more popularity. The electric power from the computer is consumed by the pen drive through the USB connector.
2. USB Mass Storage Controller/Controller Chip
The controller chip is called the brain of the pen drive. This chip helps to read or record the information/data on the NAND flash memory. It also helps to recover the data from the pen drive.
3. NAND Flash Memory Chip
The purpose of the NAND flash memory chip is to store the data. It also allows the users to erase the data stored in the pen drive so that new information can be transferred into it. The memory stored by the NAND flash chip is of non-volatile type, i.e., it does not need any power to retain the information. The primary purpose of using the NAND flash chip in the pen drive is to enhance the storage capacity. The NAND flash uses the electric circuits for storing the data and it stores the data in the forms of blocks. The NAND flash memory retains the data even when the power is cut-off as the metal oxide semiconductor layer provides the supply of an extra electric charge to retain the data. The NAND memory cells consist of two gates, i.e., control gate and floating gates. These gates help in controlling the transfer of data. The NAND gate stores the data as one byte (one word) at a time, but the data is erased in the blocks. The detailed working of the NAND flash memory chip, or we simply say the working of pen drive is explained further in this article.
4. Crystal Oscillator
The crystal oscillator is a small piece of quartz fitted in the pen drive, which vibrates at a specific frequency. It acts as a small clock inside the Pendrive, which manages the functioning/timing of each component inside the pen drive by providing accurate timings.
Other Components of Pen Drive
1. Outer Cover
It refers to the part of the USB that we see from the outside. It is generally built of plastic, metal, and sometimes wooden too. The sole purpose of the outer cover is to protect the internal components of the pen drive. Nowadays, the outer covers are also custom designed according to the user’s demands.
It is used to indicate the working condition of the Pendrive.
3. Test Points
Test points are certain locations/pins that are mounted during the manufacturing process on the pen drive. These points are used to check the working of the device and help in the repairing process in case of any failure.
4. Write Protect Switch
It is an optional component and is generally installed in pen drives if the user demands high data security. It is a tiny switch, which safeguards the data stored on the pen drive from the host devices. Pendrives with an inbuilt write-protect switch are very helpful if one is not aware of the security of the devices with which the pen drive is attached.
5. Second NAND flash Memory Chip Space
It is the additional slot, which is added into some pen drives during the manufacturing process, where another NAND flash memory chip can be installed to increase the storage capacity of the pen drive.
Understanding the Theory of Pen Drive
The chip used in the pen drive consists of a number of transistors, which acts like tiny switches. The data is stored in the pen drive in the form of 1s and 0s, and each of these values is stored at specific points in the memory. The transistor at a specific location gets switched on and allow an electric charge to flow through it to store the value ‘1.’ The pen drives are comprised of different type of transistors, which stays on/off even when there is no power supply, which is why the data remains in the pen drive even if we disconnect it from the device. A normal transistor consists of three terminals, i.e., the source, drain and gate. To easily understand the working of storage of the data in the pen drive, consider the transistor as a water pipe, the electricity flows through the transistor as the water flows through the pipe. Where the one end of the pipe from which the water enters is called the source, and another end from which the water flows away is called the drain. There is a gate between the source and the drain. When the gate is shut off, no water, i.e., no electricity flows through, hence the transistor is switched off, and the transistor stores the value zero. It stores the value one when the gate of the transistor is opened, and the electricity flows through it but if the power supply is switched off, the transistor also gets switched off. When the power is switched on, and the transistor is still switched off (due to closed gate), and we don’t know that whether the transistor was on or off before the power was switched off. In this case, the transistor forgets (loose) the information stored in it. However, the transistors used in the pen drives are different. These transistors are provided with the second gate, which lies above the first gate. When the gate is opened, some amount of electricity gets leaked and stored in between both the gates and stores the data as the value one. In this way, the data is stored in the pen drives even when the power is switched off as the electricity is still present between the gates. The stored data can be erased by draining the electricity between both gates.
Working Principle of Pen Drive
The transistors used in the pen drives are like ‘metal-oxide-semiconductor field-effect transistor (MOSFET) with the only difference that unlike MOSFET’s it has two gates instead of one. ‘Figure A’ represents the inside structure of the MOSFET used in the Pendrive. As seen from the figure, it’s an n-p-n junction, which consists of two gates, i.e., the control gate (upper gate) and the floating gate (lower gate). The gates are separate with an oxide layer through which current does not flow in the normal conditions. The transistor is switched off in this condition and has stored the value zero.
Now, let’s understand that how does it store the data. The source and the drain region of the MOSFET are built of the n-type silicon, hence they have a high number of electrons; however, these electrons cannot directly flow from the source region to the drain region as there exists an electron-deficient, i.e., P-layer between them. However, we can force the electrons to enter the drain from the source by applying the positive voltage across the two contacts of the transistor, i.e., the bit line and the word line (as shown in the image below). During this situation, some of the electrons manage to pass through the oxide layer by the tunnelling process. These electrons stay over the floating gate. The electrons present on the floating gate is what we called that the transistor has stored the data as ‘one.’ The electrons remain on the floating gate even if the positive voltage is stoped or the external power supply is switched off. The data stored can be deleted by removing the electrons from the floating gate. This can be done by applying the negative voltage on the word line. In this case, the electrons will be repelled back, and the floating gate gets clear, which eventually makes the value zero again. Hence, in this way, the data is stored and deleted in the pen drive.
Types of Pen Drive
Different types of pen drives are available depending upon the different features such as shape, size, design, and storage capacity. Some commonly used pen drives are described below.
1. OTG Pendrive
These pen drives can be directly connected to portable devices such as laptops and mobile phones. Hence, one can easily view the stored data, or transfer the data stored in the pen drives into your device.
2. Flash Drive
The Flash drives consist of different options of USB ports and different data transfer speeds, one can choose any out of them as per the requirement. Different options of USB includes USB 3.1, USB 3.2, and USB 2,0. The flash drives use flash memory for data storage.
3. Wifi Pen Drive
These pen drives do not require any port for the transfer of the data. The data can be accessed or transferred within the devices without any cable connection. You just need to connect your device with the wifi Pendrive for sharing or accessing the data. One need to plug in the wifi pen drives only at the time of charging.
5. Boot Flash Drive
The boot flash drives are specially designed pen drives, which are used to install the operating system in computers or laptops.
4. Different designed Pen Drives
Nowadays, the pen drive is available in different shapes and sizes. They are available in different designs to lure users. Some commonly used designs are
Wrist Band Pen Drives
These pen drives are available in the shape of the wrist band, i.e., they can be easily tied around the wrist.
Dummy Head Pen Drives
The body of these pen drives is designed in the shape of any character or object. One can choose any character according to his/her preference.
Keychain Pen Drives
As suggested from the name itself, these pen drives are provided with the keychain. This is a simple yet really useful feature, which helps in preventing the pen drives from getting lost easily.
5. Different Storage Capacity Pen Drives
Every pen drive is manufactured with a certain storage capacity. The commonly available storage sizes of pen drives are 128 MB, 256MB, 8GB, 32 GB, 128GB, 256GB. The latest pen drives are even available in the storage capacity of 1TB and 2TB.
Applications of Pen Drives
- The most obvious application of the pen drive is storing the data and transferring the data into different devices. One can easily view the pictures, videos, or documents by simply plugging in the pen drive with the device.
- Nowadays, pen drives are also used for marketing purposes. The cheap pen drives are given free with the main product to lure the customers. Custom-designed pen drives with the logo of the company are also used as a medium of advertisements.
- Pen drives are used for data backup. The pen drives are widely used by small businesses as a backup medium. At the end of the working day, the data is stored in the pen drive and is secured safely.
- Pen drives help in creating the password reset disk. It is the feature provided by the Windows operating system, which can be used to reset the computer password.
- Pen drives allow the user to run some applications on the computer even without installing them. The applications are stored in the pen drive and they can be run on the computers by attaching the pen drive with them. Hence, one can use pen drives as the application career.
- Pen drives are also used for the booting process. Latest designed computers or laptops allow booting from the bootable pen drives. The coding required for the booting process is installed in these pen drives, and this configuration is known as the Live USB.
Advantages of Pen Drive
- The small size and the lightweight is one of the greatest advantages of the pen drives. One can easily carry his/her data to any location by storing it in the pen drive. Unlike the other storage devices like DVDs, CDs, and floppy disks, pen drives can be easily kept in the pocket.
- With the advancement of technology, some of the latest designed pen drives, even have the capacity to store data up to TBs. Hence, pen drives come in handy to store even a large amount of data.
- Pen drives have made the process of data transfer between the devices very easy. Earlier, computers or laptops were provided with CD drives or floppy drives, which were quite complicated for the data transfers, but modern computers and laptops are provided with USB ports, and one can easily transfer the data through the pen drives.
- The transfer rate of the pen drive is very high compared to other devices, and also it is quite cheaper than the other storage devices.
- Unlike, CDs and DVDs, pen drives are not prone to any scratches.
Disadvantages of Pen Drive
Although there are numerous benefits of using pen drives, there exist certain disadvantages too, which are discussed below.
- The pen drives are not long-lasting as each pen drive consists of a limited number of program-erasable cycles, i.e., the number of times the data is stored and deleted from the pen drive. Usually, the pen drive has around 100,000 program-erasable cycles, and after this limit, the data stored in the pen drive starts becoming corrupt.
- As discussed earlier, the small size of the pen drive makes it easy to carry it to different locations, but the chances of losing the pen drive due to its small size are one of the disadvantages of pen drives. One can easily drop the pen drives from his/her pocket, which could be dangerous as it may contain confidential data which can be assessed by the other person. Hence, the pen drives are more susceptible to getting lost as compared to the CDs and DVDs.
- The pen drives are more vulnerable to getting corrupt if not kept carefully. Hence, one needs to carefully handle the pen drive to increase its shelf life.
- The major disadvantage of the pen drives is that if the pen drive consists of any virus in it, then it can spread the virus to the other devices to which it gets connected. Hence, the pen drives should always be scanned first to protect the computer from getting infected.