Memory types

Memory¶

What every programmer should know about memory, Part 1

RAM (Random Access Memory)¶

It is also called as read write memory.
It is volatile memory as the information is destroyed when power is turned off.

DRAM¶

• Constructed of tiny capacitors the leak electricity
• Requires recharge every few ms to retain the data
• Cheap
• Slower than SRAM
• Can store may bits per chip
• Uses less power
• Generates less heat
• Used for main memory

SDRAM (synchronous DRAM):
- DRAM that is synchronized with the clock speed that the microprocessor.
- Increase the number of instructions that the processor can perform in a given time.
- Speed is measured in MHz rather than in nanoseconds (ns).
- Converting between MHz and ns can be done by dividing by 1 billion. (Example 83 MHz: 1/(831000000)1000000000 = 12 ns)

SRAM¶

• Constructed from circuits similar to D-flip-flops.
• Holds contents as long as power is available
• Expencive
• Faster than DRAM
• Can not store may bits per chip
• Uses more power
• Generates more heat
• Used for CPU Cache

ROM (Read Only Memory)¶

Non-Volitile memory. Does not need electricity to keep information.
Always retains its data.

Used in embedded systems or where the programming needs no change.

PROM (Programmable read-only memory):
It can be programmed by user. Once programmed, the data and instructions in it cannot be changed.

EPROM (Erasable Programmable read only memory):
It can be reprogrammed. To erase data from it, expose it to ultra violet light. To reprogram it, erase all the previous data.

Hybrid Memory¶

NVRAM:

EEPROM (Electrically erasable programmable read only memory):
The data can be erased by applying electric field, no need of ultra violet light. We can erase only portions of the chip.

Flash Memory¶

NAND Flash:

NOR Flash:

eMMC Flash:

UFS: