Memory

Memories:

RAMs:

• SRAM (Static RAM)
• Each cell stores 1 bit
• Each cell consists of a flip flop (6 transistors)  > Large size - Low storage - High cost - More Power
• Faster than DRam

From Video: Embedded System Video 4 Memory Part 1 

• DRAM (Dynamic RAM)
• Each cell stores 1 bit
• Each cell consists of 1 transistor + 1 capacitor > Small area - High storage - Low cost - Less Power
• The smaller area than SRAM because u need 6 transistors for one cell in SRAM, while u need only one in a DRAM. The capacitor needed in DRAM cell is done built in into the transistor



From Qoura.Com

• Slower than SRam
• Mechanism
• Write '1': capacitor charge from Input buffer
• Write '0': capacitor discharge through Input buffer
• Read : capacitor discharges through Output buffer
• Then capacitor is recharged (refreshes through Refresh buffer)
• Examples:
• SDRAM (Synchronous DRAM)
• DDR SDRAM (Double Data Rate SDRAM)

From Video: Embedded System Video 4 Memory Part 1 

• SRAM Vs DRAM

From Video: Embedded System Video 4 Memory Part 1 

Cache Memory:

• Is used to save portions of the data and instructions, that are currently used by the processor
• Requirements:
• Storage capacity can be small.
• Fast
• Used RAM:
• SRAM (Faster - Less Storage capacity)

Main Memory:

• The Big Ram that shall contain all the system data
• Requirements:
• Big storage capacity
• Speed can be less than cache
• Used RAM:
• DRAM (Not as fast as SRAM - high storage capacity)

ROMs:

• Mask ROM
• Programmed in factory
• PROM
• Contains fuses, can be programmed only once
• EPROM (Erasable Programmable ROM)
• Ex: Ultra Violet EPROM, can be erased using ultraviolet light, then reprogrammed
• Slow
• EEPROM (Electrically Erasable Programmable ROM)
• Flash memory: CMOS transistor with floating gate
• Hard disk
• Magnetic storage.
• Very Slow, Large capacitance, used for long term data storage
• Solid State Desk
• Like hard disk, but faster