Semiconductor memory facts for kids

Semiconductor memory is like a super-fast electronic notebook for computers. It's a special kind of computer memory that stores digital information. Think of it as the brain's short-term memory, where the computer keeps everything it's working on right now.

These memory devices are built on tiny silicon chips called memory chips. They use tiny electronic switches called transistors to hold information. There are many types, but the main ones are random-access memory (RAM) and non-volatile memory (like flash memory).

Semiconductor memory is super quick! It can find any piece of information in the blink of an eye, much faster than older storage like hard disks or CDs. This speed is why it's used for the computer's main workspace, holding programs and data while you use them.

How Semiconductor Memory Works

In a semiconductor memory chip, each tiny piece of information, called a bit (a 0 or a 1), is stored in a small circuit called a memory cell. These cells are arranged in rows and columns on the chip.

Memory cells are grouped into small units called words. A word is like a small packet of bits, often 8 bits long (which is called a byte). When the computer wants to find information, it uses a special number called a memory address. This address tells the chip exactly which word to access.

The two main things a memory chip can do are:

• Read: This means the computer looks at the data stored in a memory word without changing it.
• Write: This means the computer puts new data into a memory word, replacing anything that was there before.

Besides being in separate memory chips, semiconductor memory is also built into other important computer parts, like the microprocessor (the computer's main brain).

Types of Semiconductor Memory

There are two big families of semiconductor memory:

Volatile Memory

RAM chips for computers usually come on removable memory modules like these. Additional memory can be added to the computer by plugging in additional modules.

Volatile memory is like a whiteboard. It loses all its stored information when the power is turned off. But it's very fast and usually less expensive. This type is used for the main memory in most computers because the computer saves important data to the hard disk before shutting down.

• RAM (Random-access memory)
  • DRAM (Dynamic random-access memory)

DRAM is the most common type of RAM in computers. Each memory cell uses one transistor and one tiny capacitor to store a bit of data. It's very dense (can store a lot of data) and affordable. However, the data stored in DRAM slowly fades away, so it needs to be refreshed (rewritten) constantly. The computer handles this refresh process automatically.

• • • SDRAM (Synchronous dynamic random-access memory)

This is a faster type of DRAM that works in sync with the computer's clock. This allows it to process many memory requests at once, making it much quicker.

• • • • DDR SDRAM (Double Data Rate SDRAM)

DDR SDRAM is a super popular type of SDRAM. It can transfer data twice as fast as regular SDRAM by sending data on both the rising and falling edges of the clock signal. Newer versions like DDR2, DDR3, and DDR4 transfer even more data at once, making computers even faster.

• • • HBM (High Bandwidth Memory)

This is a very fast type of SDRAM used in powerful graphics cards. It's made by stacking many memory chips on top of each other, allowing for a wider and faster data path.

• • SRAM (Static random-access memory)

SRAM stores each bit of data using a circuit called a flip-flop, which uses several transistors. SRAM is faster than DRAM and doesn't need to be refreshed. However, it's more expensive and takes up more space, so it's usually used for smaller, very fast cache memory inside computer processors.

Non-Volatile Memory

Non-volatile memory (NVM) is like a permanent marker. It keeps its stored information even when the power is off. This makes it perfect for portable devices, memory cards, and storing important system software.

• ROM (Read-only memory)

ROM is designed to hold data that doesn't change often, like the basic instructions a computer needs to start up (the BIOS). It's usually only read from, not written to, in normal use.

• • EPROM (Erasable programmable read-only memory)

4M EPROM, showing transparent window used to erase the chip

EPROM chips can be erased and rewritten. To erase them, you have to take the chip out of the circuit and expose a special window on top to ultraviolet light. Then, you can reprogram it.

• • EEPROM (Electrically erasable programmable read-only memory)

EEPROM chips can be rewritten electrically, even while they are still in the circuit. This is useful for updating firmware, which is the software that controls hardware devices.

• Flash memory

Flash memory is a very popular type of non-volatile memory. It's faster to write to than EEPROM but not as fast as RAM. It's often used like a small hard disk to store files in portable devices such as USB flash drives, digital cameras, and cellphones.

History of Semiconductor Memory

The idea of using electronic parts for memory started in the 1960s. Early computer memory used magnetic cores, which were small donut-shaped magnets.

MOS Memory

A big breakthrough happened with the invention of the metal–oxide–semiconductor field-effect transistor (MOSFET) in 1959 by Mohamed M. Atalla and Dawon Kahng. This new transistor made it possible to build memory chips that were smaller, cheaper, and used less power than magnetic cores.

• MOS SRAM: The first MOS SRAM was developed in 1964. It became an alternative to magnetic core memory.
• MOS DRAM: In 1966, Robert H. Dennard at IBM invented the single-transistor DRAM memory cell. This was a huge step! The first commercial DRAM chip, the Intel 1103, came out in 1970.
• Flash Memory: Fujio Masuoka at Toshiba invented flash memory in the early 1980s. This led to the flash drives and memory cards we use today.

By the early 1970s, MOS memory had replaced magnetic core memory as the main way to store information in computers.

What Semiconductor Memory is Used For

Here's a quick look at where different types of semiconductor memory are used:

See also

In Spanish: Memoria de semiconductor para niños

• List of best-selling electronic devices
• Semiconductor industry