Thank you for being part of the FixData community! In this issue, you will find several topics about USB, as well as a special invitation to our next webinar.

• Anatomy of the USB

• Page structure in USB drivers

• Video: My laptop does not recognize my USB - SOLUTIONS

• How to recover data from a USB flash drive?

• Webinar Invitation ⭐

• Premium Content: XOR encoding in NAND memories

Anatomy of the USB

With the passage of time and the need to be able to transport information from one place to another in a more compact and simple way, a device was developed that met these characteristics and was capable of storing information. This is how the USB memory arises, a device capable of storing a certain amount of information in a memory and with the ease of transport, thanks to its compact and lightweight design.

The name USB is an acronym that refers to "Universal Serial Bus", which is a communication port between the storage device and another device where the USB flash drive can be connected.

USB flash drives have three components that are essential for their operation, without them it would not be possible to communicate the device with the outside or store information.

These components are the following:

• USB Type A Connector: The USB connector is responsible for making the connection with the devices where the USB memory is connected, through this port is the means by which energy is transferred to power all components of the USB memory and can function properly. In addition to being the data bus, whether it is going to write to the memory or read information.

• Controller: The controller is in charge of coordinating the information that enters and leaves the memory, it manages in which cells of the NAND memory the information will be stored and at the moment of reading the data it is in charge of extracting the bits of the cells for its structuring and later on its visualization.

• NAND memory: The NAND memory is in charge of storing the information that is transferred to the memory. Depending on the type of architecture that manages the memory is how it will store the bits in the cells, there are four types of structures to store information:

  • Single Level Cell (SLC): Only allows one bit per cell.

  • Multi-level cell (MLC): Allows two bits per cell.

  • Triple-level cell (TLC): Allows three bits per cell.

  • Quad-level cell (QLC): Allows four bits per cell.

This is how NAND memory manages to safeguard the information sent in its storage cells.

These 3 components are the most essential for the operation of a USB memory, this is how together they manage to be one of the most used storage devices.

Page structure in USB drivers

The USB flash drives are storage devices, which are characterized by a compact size and ease of transport, usually do not meet large memory capacities, but are very useful in everyday life.

Being a storage device, the USB flash drive performs different processes inside, which makes it can safeguard the information, one of them are the pages, these are responsible for maintaining a structure in how the information is stored in the memory, having physical parameters which can not be changed. 

The controller of the USB flash drives is in charge of determining which page structure will be followed for the storage of the information. 

There are different brands of controllers, in this case we will talk about:

• Phison 

• Silicon Motion 

• Innostor

• Sandisk

In this article, we will visualize the page structure of the previously mentioned controller vendors. 

As already mentioned, the pages are a structure for the accommodation of information within the NAND memory chips, but depending on the controller is the structure that will have the information, the pages usually have specific sizes and each page is associated with the following fields that make it up, such as the data field, a SA field and the ECC field.

The space determined for the user's data is usually divided into small fragments that can range from 512 bytes, 1024 bytes to 2048 bytes.

The estimated size for each page will be different, depending on the type of controller the storage unit has, since the elements that make up the page may vary in size.

Data field (DATA):

In this field we can have 3 different sizes:

• 512 bytes: this storage size is common to see in older devices, where XOR coding was not incorporated.

• 1024 bytes: this type of size is used in most of the current devices, where XOR encoding is used, they are modern flash memories. 

• 2048 bytes: typically used in Sandisk brand devices.

Service Area (SA) field: 

The SA has the control bytes that help data redirection, its composition is formed by a header and a logical block number LBN.

The size that this area has set depends on the controller.

ECC field:

The ECC field, is a code focused on error correction in the unit. It can have a size in the range of 10 to 240 bytes per data fragment.

This is how the pages are structured in the NAND memory of USB flash drives. 

My laptop does not recognize my USB - SOLUTIONS

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How to recover data from a USB flash drive?

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