Main Memory (Memory) ROM, RAM
Main Memory (Memory)
Overview of ROM/ROM BIOS
ROM (Read Only Memory) is a read-only memory element and is used in computers to store the BIOS.
The Basic Input/Output System is the basic program for operating a computer.
It contains basic information about each device in the computer and diagnoses each device.
When the power is turned on, it starts the computer and diagnoses itself. The BIOS must never be erased, so it is stored in ROM, which is non-volatile memory.
RAM
RAM (Random Access Memory) is also called RWM (Read Write Memory). Because all information stored inside disappears when the computer is turned off, it is called volatile memory. RAM is a memory device that allows data to be read and written freely. Since it is volatile, all contents in memory are erased when power is cut off.
How DRAM Stores Data
DRAM (Dynamic RAM) stores data using the principle that capacitors store electricity. What we call data in a computer is actually the flow of electrical signals. Computer data is represented by 1s and 0s, which respectively mean a state where electricity flows and a state where it does not. If this electrical state can be maintained, that is storage. The most common media for storing electricity are electronic components called capacitors or batteries.
For example, to store the data 10101010, prepare eight capacitors and store the data by charging those corresponding to 1 and not charging those corresponding to 0. This stores the data 10101010. DRAM is a device that stores data using this capacitor principle.
However, electricity once stored in a capacitor or battery does not last forever. Even when it is not used, natural discharge occurs, and after a certain amount of time data is lost. Therefore, RAM performs a refresh, or recharge, operation to maintain its current state before data is lost. When the computer is turned off, RAM cannot perform this refresh, so the data is lost. In other words, it has volatile properties. DRAM has long been used as an element for computer main memory because its principle is simple and it is easy to manufacture, but it is now being improved into new forms because refresh operations increase waiting time.
Types of RAM
| Category | DRAM | SRAM |
|---|---|---|
| Refresh | Required | Not required |
| Access speed | Slow | Fast |
| Circuit structure | Simple | Complex |
| Integration density | High | Low |
| Price | Cheap | Expensive |
| Use | Main memory | Cache memory |
| Comparison of DRAM and SRAM |
Types of DRAM
SDRAM
SDRAM is DRAM whose clock speed is synchronized with the microprocessor. Clock speed synchronization helps increase the number of instructions the processor can execute within a given time.
DDR SDRAM
DDR (Double Data Rate) memory SDRAM is the name given to memory that can transfer twice as much data as previous SDRAM. DDR memory has two standards, PC2100 and PC1600, but they do not actually operate at 2100 MHz and 1600 MHz respectively. DDR SDRAM operating on a 100 MHz memory bus has a speed around PC200, and when operating on a 133 MHz bus, around PC266.
DDR2 SDRAM
DRAM that improves the operating speed of DDR SDRAM by two times.
Rambus DRAM
Rambus DRAM is DRAM connected through the Rambus Channel, a data transfer bus developed by the American company Rambus. This channel uses a 9-bit bus and transfers data synchronized with a 250 MHz clock.