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There are two types of memory, primary memory and secondary memory.

1. Primary memory:

Primary memory is directly addressed by the processor.

i) RAM: (Random Access Memory) Read or write memory. It stores temporary data and stack.

• Static RAM- Data is stored in the form of voltage. It is made up of flip flops. It is realized using 6 transistors. 4 transistors are part of flip flop and two transistors are for control access.
• Dynamic RAM- It stores data in the form of charge. It is made up of MOS transistors. The circuit has 1 MOSFET and a capacitor.

ii) ROM: (Read Only Memory)

It stores application programs from where processor fetches instruction code. It stores codes for system booting and RTOS. It retains content even after system is turned off. It is a non-volatile storage memory.

• Masked ROM- It is a one-time programmable device. It uses hard wired technology for storing data. Low Cost and high volume production are its advantages.
• PROM- The end user is responsible for programming device. It has Nichrome or polysilicon wires.
• EPROM- It is Erasable Programmable Read Only Memory. The information is stored in the form of bits. Reprogramming is possible. Data is erased by exposing window to UV rays.
• EEPROM- It is Electrically Erasable Programmable Read Only Memory. The information is altered using electrical signals.
• Flash- It is the ROM technology used in embedded system. It combines re-programmability of EEPROM and high capacity of standard ROMs.

2. Secondary memory:

Secondary memory is not directly addressed by the processor. Programs and data are kept on a long term basis. It has enormous storage capacity as compared to primary memory.