MEMORIES IN DIGITAL ELECTRONICS

In computers, memory is the most essential component for the normal functioning of any system – to store data, to perform calculations, to do complex operations, etc. We know that almost all our information and data is stored in the Hard Disk within the CPU. The Hard Disk/Hard Drive/Hard Disk Drive has the most extensive memory in the computer system. But a lot of important data of a computing device is stored in what we will study in this article known as primary memory.

Ask yourself, is it sensible to access the hard disk for every small action? If we need to find a piece of simple information, is it worth to have the computer browse through Gigabytes of memory for just one minor information? Doesn’t this compromise the efficiency of the system? Shouldn’t there be separate memory systems that deal with the data critical for the computer’s operation?

Primary and Secondary Computer Memory

Apart from the HDD, our computer has two other types of memory present. These memory types are used in storing small amounts of memory, or frequently used data which needs to be easily accessed. The two major types are:

• Primary memory (RAM and ROM) and
• Secondary memory (Hard Drive, CD, etc.).

The Primary Memory is also known as system memory, whereas the Secondary Memory is called the Storage. The Secondary memory is physically located within a distinct storage devices, such as an HDD or a solid-state drive (SSD).

1) Primary Memory (Main Memory)

It is also referred to as Main Memory. It is volatile. The reason behind is, Primary memory holds only those data and instructions on which the computer is currently working that is it does not store the data permanently.

• It also stores the operating system and data required to run the computer.
• It is a limited capacity memory and data or information is lost when power is switched off. Primary Memory is generally constructed with a semiconductor device.
• Registers are much faster than these memories but it is faster than secondary memory.
• It contains all the data and instructions that are required to be processed.

It is further divided into two subcategories RAM and ROM.

i) RAM (Random Access Memory)

It is Random Access Memory because of the random selection of memory locations. It performs both read and writes operations on memory. It stores data temporarily.

If power failures happen in the system during memory access then you will lose your data permanently. So, RAM is a volatile memory.

RAM categorized into following types:

1. DRAM
2. SRAM

a) SRAM (Static random access memory)

It holds data in a static form, that is, as long as the memory has the power as the dynamic RAM, it is not needed to refresh it again and again.

• Static RAM provides faster access to data and is more expensive than DRAM as each cell must contain multiple transistors.
• SRAM does not use capacitors.
• SRAM is also highly recommended for use in PCs, peripheral equipment, printers, LCD screens, hard disk buffers, router buffers and buffers in CDROM / CDRW drives.

b) Dynamic RAM (Dynamic random access memory)

It is a type of random-access memory used in computing devices. It is made up of capacitors and transistors.

• This type of memory uses separate capacitors or transistors to stores each bit of data and it has two states of value in one bit called 0 and 1.
• As compared with other RAM's it is less expensive.
• Data were written by DRAM at the byte-level.
• In DRAM, data is written at the byte-level and it reads data at the multiple-byte page level.
• DRAM requires less power than other RAMs.

ii) ROM (Read Only Memory)

ROM offers huge types of standards to save data as it is a permanent memory location. But it works with the read-only operation. whenever power failure occurs during the ROM memory work in computers then no data lose happens.

• It is Used where the programming requires no change and also in embedded systems or.
• It is Used in peripheral devices and calculators.

Types of Read Only Memory (ROM)

1. PROM (Programmable read-only memory)
2. EPROM (Erasable Programmable read only memory)
3. EEPROM (Electrically erasable programmable read only memory)

a) PROM (Programmable read-only memory)

Developers created a type of ROM known as programmable read-only memory (PROM) because Creating ROM chips from scratch are time-consuming and very expensive.

• It can be coded by the user. Once coded, the data and instructions in it cannot be changed.
• It is used to store permanent data in digital electronic devices.
• It can be bought at a low cost as compared to other RAMs.

b) EPROM (Erasable Programmable read only memory)

This is the type of memory that can be reprogrammed. We can erase data from it and reprogram it that is erase all the previous data by using high voltage Ultraviolet light.

• It is required to erase each cell in EPROM.

c) EEPROM (Electrically erasable programmable read only memory)

The data can be erased and reprogrammed by applying an electric charge. There is no need for ultraviolet light and we can erase only portions of the chip.

• It was a replacement for PROM and EPROM chips and later it is used for computer's BIOS.
• Configurations parameters are stored by using EEPROM. In modern computers, they replaced BIOS CMOS memory.
• It is required that data to be written or erased by EEPROM one byte at a time.