Volatile memory is computer memory, which requires the presence of electricity to store information (as opposed to non-volatile). While the power source is connected to this type of memory, data is saved. As soon as it turns off, information is quickly lost.
There are several applications for volatile memory devices. They can even be used as the main data warehouse. Their key advantage over hard drives is the fast speed of information exchange. In addition, the volatility feature helps protect restricted information because it becomes inaccessible when the power source is turned off. Most types of random access memory (Random-Access Memory, RAM) are volatile.
The following main types of volatile memory exist:
Static memory
The main advantage of static RAM (Static RAM, SRAM) is that it is much faster than dynamic. Its disadvantage is the high price. Static memory does not require continuous regeneration. But at the same time, it needs a continuous current to maintain the voltage difference. To store one bit of information, the static memory chip uses a cell of 6 transistors.
Four transistors M1-M4 form 2 inverters with cross feedback and are directly used to store one bit of data. A memory cell has 2 stable states that are needed to store 0 or 1. An additional two transistors control access to the memory cell during data read and write operations.
Static Power Consumption
Power consumption depends on how often you access static volatile memory, but overall it matters little. Sometimes it can consume as much power as dynamic memory (when used at high frequencies). On the other hand, when it is in the standby state, it consumes a very small amount of electricity: a few micro watts.
Applying static memory
Static memory built into the chip is used:
- as RAM or cache memory in 32-bit microcontrollers;
- as the main cache in powerful processors, for example, the X86 family;
- in special purpose integrated circuits (ASICs);
- in user-programmable gate arrays (FPGA);
- in programmable logic integrated circuits (FPGAs, CPLD).
In addition, static volatile memory is used:
- in scientific and industrial subsystems, in automotive electronics;
- in personal computers, routers and peripheral equipment as the internal cache of the processor and the buffer of the hard disk or router;
- in liquid crystal displays (LCDs) and printers for storing a displayed or printed image.
Advantages and disadvantages of static memory
Pros:
- low power consumption;
- simplicity (no regeneration scheme is required);
- reliability.
Minuses:
- high price;
- small capacity;
- big sizes;
- changing power consumption.
Dynamic memory
Despite the fact that both types of volatile memory require an electric current to save data, they have some differences. Dynamic random access memory (dynamic RAM, DRAM) is very popular due to its efficiency and cost. To store one bit of information in DRAM on the integrated circuit uses one capacitor and one transistor. This allows you to effectively use the space of the integrated circuit and makes the named type of memory inexpensive.
Memory regeneration
The process of periodically reading information from cells in a computer memory and immediately overwriting it in the same cells without change is called memory regeneration. This is a background process for storing data in dynamic volatile memory. It is a defining characteristic for such a variety.
Information in dynamic memory is stored as the presence or absence of charge on a miniature capacitor. Over time, the charge decreases. Therefore, if the data is not regenerated in a timely manner, they can be completely lost. To protect against data loss, they are periodically read and rewritten using an external circuit. As a result, the capacitor charge is restored to its original state.
Types of Dynamic Memory
Asynchronous dynamic memory is the first type of DRAM that appeared in the late 1960s. It was actively used until 1997, until it was replaced by synchronous DRAM. The memory is called asynchronous due to the fact that access to it is not synchronized with the clock signal of a computer system.
Synchronous dynamic memory is widely used in modern mechanisms. This type of volatile computer memory responds to read and write signals synchronously with the system clock signal. Synchronous memory runs at higher speeds compared to asynchronous. Since 1993, this type has been predominant in the personal computers of users around the world.
Initially, synchronous dynamic memory was called SDRAM. In the future, the data transfer rate increased by 2 times and the memory appeared on the market under the name DDR1. Subsequently, DDR2, DDR3, and DDR4 were released. The latest generation (DDR4) was created in the second half of 2014. In March 2017, the development of volatile DDR5 memory devices began.