- Registers are parts of CPU with least capacity for storage. It is responsible for storing extremely limited amount of data & instructions instantly before and after processing
- Registers can use as lower 8 bits and higher 8 bit, means 16 bit or 32 bit registers.
- Registers include accumulator, base index register, and count register and data known as General Purpose Registers.
- They are used for I/O operations, counter loop etc.
RAM: (Random Access memory)
- Its storage capacity is more than registers but less the secondary storage device.
- It is temporary and volatile.
- RAM chips lose their contents if current lost or turned off.
- When we start most software programs the entire program is brought from secondary storage into RAM.
- There are two main types of RAM.
- DRAM or Dynamic RAM.
- SRAM or Static RAM.
- It stores the data in the form of an electric charge. This charge decreases time.
- In order to maintain data in DRAM the chip is recharged or refreshed frequently.
- During refreshing time computer cannot access DRAM.
- This type of memory used in old microcomputers.
- Memory cells are made of digital gates.
- These gates can hold data without any need for frequent recharging.
- SRAM is used in modern computers.
ROM: (Read Only Memory)
- ROM is non-volatile memory and retains the instruction when the power to the computer turned off.
- The instruction in ROM can only be read by the computer and cannot be changed by the user.
- Vendor has written it.
There are several variations of ROM
- PROM (Programmable read-only memory) consists of a blank chip on which the user can place data and programs.
- EPROM (Erasable Programmable read-only memory): are similar to PROM but it can be erased and reprogrammed.
- EEPROM (Electrically Erasable Programmable read-only memory): are similar to EPROM but it can be easier to erased and reprogrammed. It is most flexible type of ROM.
- High-speed memory that the processor can access more rapidly that main memory (RAM).
- It stores blocks instructions used most often by the CPU.
- Block instruction used less often remains in RAM and infrequently stored in storage devices.
There are two types of cache memory
- L1 (level 1 cache) located in the processor.
- L2 (level 2 cache) on the motherboard.
- Flash memory is a type of nonvolatile memory that can be erased electronically and rewritten, similar to EEPROM
- Most computers use flash memory to hold their startup instruction because it allows the computer easily to update contents.
- Flash memory also store data and programs on many mobile computer devices.