Flash memory in a computer is a non-volatile memory. Flash memory was built with a similar approach as that of EEPROM. Like EEPROM it is possible to read the contents of a single cell of the flash memory. But, unlike EEROM it is possible to write the entire block of the flash memory. but before writing to the block the entire data of the block must be erased.
Flash memory requires different voltages to read, write and erase the data. Let us learn more about flash memory in the following section.
Flash Memory in Computer
- What is Flash Memory?
- How Flash Memory Works?
- Types of Flash Memory
- Advantages And Disadvantages
What is Flash Memory?
Flash memory is a storage device that uses a technology that helps the cells of flash memory to remember their state before being switched off. Flash memory is being used in many consumer electronics products such as USB storage, MP3 players, GPS devices, digital cameras, smartphones, etc.
SSDs also use flash memory and nowadays it is rapidly replacing HDDs. Flash memory has higher cell density which facilitates it to have higher capacity. Flash memory has a lower cost per bit and even consumes less power.
How Flash Memory Works?
The memory cell of a flash memory is built up of a single transistor controlled by the charge trapped in it. In a memory chip, the transistor acts as a switch that enables the memory cell to change its state.
The conventional transistors are controlled by electricity i.e., the system uses different electric patterns to read, write, and erase data. But as soon as power is removed the transistors return to their original state. This is characteristic of random-access memory (RAM).
Now, if we talk of ROM the read-only memory does not lose data when power is removed. The flash memory shares are characteristic of both RAM and ROM. Like RAM the data can be written, erased, and rewritten and like ROM, the flash memory retains the data even after the power switches off. To achieve this the flash memory uses a unique type of transistor that retains its content regardless of the fact whether the power is on or off.
Second Floating Gate in Flash Memory
Flash memory uses a transistor that features a second floating gate. Usually, the conventional transistor has three connections source, drain, and gate. The current enters through the source, escapes through the drain and the gate can block the current flow.
When the gate is off there is no current flow and the state of the transistor is off (0). When the gate is on, the power can flow through the transistor resulting in its state of (1). Usually, when the power is switched off the transistor also shuts down. When the user restarts the computer, the transistor remained off and becomes difficult to identify whether the transistor was on or off before the power is switched off.
But the transistor of the flash memory has a third connection which is nothing but another floating gate at the top of the first gate. This arrangement makes sure that even if the power is switched off electricity doesn’t drain out and keeps on circulating across these two gates.
Types of Flash Memory
We can categorize flash memory into two types NAND flash and NOR flash. In the year 1988, Intel introduced the first flash memory which was NOR flash memory. Later in 1989, Toshiba introduced NAND flash memory. NAND and NOR flash were named so because of the way the floating gates of memory cells are interconnected in configuration. The floating gate truly resembles the NOR and NAND logic gates thus the memories were named NAND and NOR flash memory.
The logical organization of NOR flash resembles as NOR logic gate. With high-speed random access, it can read and write data to the specific location of the memory. In NOR flash memory we can refer to and retrieve a single byte.
We use NOR flash memory to store the operating system of cell phones. In the Windows operating system, we use NOR flash memory to store the BIOS programs that run during the system start-up.
The NAND flash memory reads and writes data in small blocks. Here each block may consist of hundreds or thousands of bits. This kind of flash memory is used in portable devices such as USB flash drives, memory cards of digital cameras, MP3 players, SSD, etc. Though NAND flash has higher bit density with greater writing speed, it does not provide random access.
The following are examples of flash memory.
- Multimedia card (MMC) – It is used as a solid-state storage in your smartphones, digital cameras, MP3 players, etc.
- Solid State Drive (SSD) – This a flash drive that is nowadays rapidly replacing the hard drive.
- USB Flash Drive – It is a portable storage tool that we use to transfer data.
- BIOS Chip – It is used in computers to store the instruction that the computer requires to perform its basic functions such as booting and keyboard control.
- It Consumes low power and generates less heat as compared to HDD.
- Lower cost per bit.
- Feasible to be used for portable, battery-powered equipment.
- It is a non-volatile memory that retains data even if the power is off.
- It is a higher bit density with great speed.
- The flash memories are durable as they do not contain a mechanical part.
- The memory cells of flash drives wear out after a definite number of write and erase.
In this way, the flash memory in a computer is composed of NOR or NAND logic gates. It is a non-volatile memory. The flash memory is named like this because the section of a flash memory cell can be erased in a flash.