What is Semiconductor Memory? [GATE Notes]

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Semiconductor memory refers to electronic data storage devices that use semiconductor technology to store digital data. These memories are widely used in various electronic devices, including computers, smartphones, tablets, digital cameras, and many others. There are two main types of semiconductor memory: volatile and non-volatile. Semiconductor memory is characterized by its speed, density, and cost.

Semiconductor Memory Notes PDF(Download)

Semiconductor memory has revolutionized the field of computing and digital electronics, enabling the development of faster, smaller, and more powerful devices. In this article, Candidates can find study notes on semiconductor memory which cover the topics such as memory, RAM, and ROM and some basic concepts related to PLA, PAL, and FPFA.

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What is Semiconductor Memory?

Semiconductor memory is a type of digital memory technology that uses semiconductors, such as silicon, to store and retrieve digital data. It is commonly used in electronic devices, such as computers, smartphones, and other digital devices, as a primary or secondary storage medium. The memory implemented using the semiconductor chips is semiconductor memory.

Semiconductor memory can be divided into two main categories: volatile and non-volatile memory. Volatile memory, such as dynamic random-access memory (DRAM) and static random-access memory (SRAM), requires power to retain stored data. Non-volatile memory, such as read-only memory (ROM), flash memory, and Electrically Erasable Programmable Read-Only Memory (EEPROM), can retain data even when power is turned off. Various differences between volatile and non-volatile memory are there.

Semiconductor memory has several advantages over other types of memory, including faster access times, higher data transfer rates, and lower power consumption. These benefits make it an ideal storage medium for a wide range of electronic devices and applications.

The semiconductor main memory subsystem includes a critical component of a computer system that stores and retrieves data and instructions needed by the processor to perform tasks.

Types of Semiconductor Memory

Semiconductor memory is a type of electronic memory that uses semiconductor devices such as transistors to store digital information. Semiconductor memory is widely used in modern electronic devices such as computers, mobile phones, and digital cameras. Here are the main types of semiconductor memory:

Semiconductor Memory and its Types

  1. Random Access Memory (RAM): RAM is a type of volatile memory that can be read and written to. RAM is used as temporary storage for data and program instructions when the computer is running. RAM is further divided into two types:

    a. Static RAM (SRAM): SRAM is a type of RAM that uses flip-flops to store each bit of data. SRAM is faster and more expensive than DRAM.

    b. Dynamic RAM (DRAM): DRAM is a type of RAM that uses capacitors to store each bit of data. DRAM is slower and less expensive than SRAM.

  2. Read-Only Memory (ROM): ROM is a type of non-volatile memory that can only be read, not written to. ROM is used to store program instructions and data that are not intended to be modified. ROM is further divided into two types:

    a. Mask ROM: Mask ROM is a type of ROM that is programmed during the manufacturing process. Once programmed, the contents of the ROM cannot be changed.

    b. Programmable ROM (PROM): PROM is a type of ROM that can be programmed once by the user. Once programmed, the contents of the PROM cannot be changed.

  3. Electrically Erasable Programmable Read-Only Memory (EEPROM): EEPROM is a type of non-volatile memory that can be programmed and erased electrically. EEPROM is used to store data that needs to be modified occasionally, such as the BIOS settings on a computer motherboard.

  4. Flash Memory: Flash memory is a type of non-volatile memory that can be electrically erased and reprogrammed. Flash memory is used in a wide range of electronic devices such as USB drives, digital cameras, and mobile phones. Flash memory is further divided into two types:

    a. NOR Flash: NOR gate flash is used for executing code directly from the memory. It has a slower write speed but a faster read speed.

    b. NAND Flash: NAND gate flash is used for data storage. It has a faster write speed but a slower read speed.

Registers and their Types

Registers are memories located within the Central Processing Unit (CPU). Various types of registers are available within the CPU. Registers are small but the CPU can access them quickly. Some of the registers available in the system are given below.

  • Instruction Register
  • ALU I/O registers
  • Status Register
  • Stack pointer register
  • The program counter, etc.

What is Dynamic RAM (DRAM)?

In this type of RAM, data is stored on capacitors and requires periodic refreshments. Here a few points about the dynamic RAM are described below.
  • Data is stored in MOS capacity.
  • Only MOSFET is used for implementation.
  • It is Slow compared to Static RAM.
  • Dissipate less power.
  • The memory capacity of Dynamic RAM is more.
  • It can be used as the Main memory.
  • Refreshing is required.

Advantages of Static RAM Over Dynamic RAM

Static RAM and Dynamic RAM both are types of Read Acess Memory. It can be used for the purpose of data storage. Here few differences between SRAM and DRAM are discussed below.

  • The access time of SRAM is less and thus these memories are faster memories.
  • As SRAM consists of flip-flops thus, refreshing is not required.
  • Less number of memory cells are required in SRAM for a unit area.

Read Only Memory (ROM) and Their Classifications

It is non-volatile memory, implemented using the combinational circuit. It is also known as masked memory.

Classification of ROM

  1. Mask-programmed ROM: The required contents of the memory are programmed during fabrication. Data stored this way can never be altered. It can be implemented using Fixed AND Fixed OR Circuit.
  2. PROM (Programmable ROM): Required content is written in a permanent way by burning out internal interconnections (fuses). It is a one-off procedure. It can be implemented using Fixed AND Programmable Circuits.
  3. EPROM (Erasable PROM): Data is stored as a charge on an isolated gate capacitor (“floating gate”). Data is removed by exposing the PROM to ultraviolet light.
  4. EEPROM (Electrically Erasable PROM): It is also called Flash Memory. The content can be re-programmed by applying suitable voltages to the EEPROM pins. Flash Memories are very important data storage devices for mobile applications.

Programmable Logic Devices

Programmable logic devices are a special type of IC. Different types of logic functions can be implemented using a single programmed IC chip of PLD. PLDs can be reprogrammed because these are based on rewritable memory technologies. PLDs are divided into three types. They are PLA, PAL, and FPGA.

Programmable Logic Array (PLA)

  • PLA is implemented using AND-OR gate arrays and programmed for specific logic functions.
  • It is used where the number of don’t care conditions are excessive.
  • In PLA’s both AND and OR arrays are programmable.
  • The AND and OR gates are fixed for any PLA chip.
  • It depends on the number of inputs and outputs of PLA.
  • Combinational circuits, Sequential Circuits, and Compact circuits can be implemented using PLAs.

Programmable Array Logic (PAL)

  • PAL is implemented using AND gate arrays are programmable and OR gate arrays are fixed.
  • Because only AND gates are programmable, the PAL is easier to program, but it is not as flexible as the PLA (programmable logic array).

Field Programmable Gate Array (FPGA)

  • It is a semiconductor device that is comprised of a different number of logic elements, interconnects, and Input/Output blocks. All these components are user-configurable.
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