Types of RAMS

RAM is volatile memory, which means that it can't retain data once the power is turned off. Its advantage is the high access speed. RAM types are as shown like the following picture:

RAM is mainly divided into two types: DRAM (Dynamic RAM) and SRAM (Static RAM). SRAM: It relies on static flip-flops to store data. Therefore, the information that is stored in SRAM can be retained for a long time without having an power failure and no additional circuit refresh is required.DRAM: It uses capacitors to store information to helps (charge), but any capacitor has leakage of (charge loss), so the stored information will be lost if Charge is loss. To solve this problem, DRAM needs to read and rewrite (so-called refresh) the DRAM at regular intervals of (2ms). Comparing SRAM and DRAM, and their differences are as follows: SRAM: It requires about six transistors for a memory cell, which makes it high-cost of, small-capacity, and high-speed. Therefore, it is often used as the primary cache or secondary cache of the CPU. DRAM: It requires about one transistor and one capacitor for a memory cell, which makes it have lower-cost and large-capacity, but it needs to be refreshed but the speed is slower than SRAM. Therefore, it is often used as the main memory inside of the computer. FPM (Fast Page Mode): It is an earlier type of PC memory and has been deprecated. When it comes to reading data, it will need to wait for the first bit of data to be read before starting to read the next data. In addition, data is transmitted every 3 clock pulse cycles. The max transfer rate is around 176 Mbps. EDO DRAM (Extended Data Output DRAM): It has been deprecated, too. It doesn't wait for the completion of the processing of the first bit before it continues to use the next one. In addition, data is transmitted every 2 clock pulse cycles. ADRAM (Asynchronous DRAM): Earlier DRAMs are mainly ADRAMs. In ADRAMs, the system clock doesn't coordinate or synchronize to the memory access point. Therefore, there is delay in the response of the memory. SDRAM (Synchronous DRAM): To solve the problem of ADRAM, SDRAM comes out. In SDRAMs, the system clock coordinates or synchronizes memory access. Therefore, the CPU will know the timing between the exact cycle number of the available data on the RAM, on the input bus, and the output bus, which helps improve the read and write speed of the memory. DDR SDRAM (Double-Data-Rate SDRAM): DDR SDRAM is based on SDRAM. SDRAM transmits data and only once in a clock cycle it usually transmits data in the rising period of the clock. As for DDR SDRAM, it will transmit data twice in a clock cycle and it can transmit data once in the rising and falling periods of the clock, respectively. RDRAM (Rambus DRAM): Unlike DDR and SDRAM, it uses a serial data transfer mode. This mode requires manufacturers to change the manufacturing process and, to produce RDRAM, manufacturers must pay a certain patent fee. Therefore, it has high-cost. That is also why it is not so popular among users. CDRAM (Cached DRAM): This memory is a special type of DRAM memory with an on-chip cache memory (SRAM) that will act as a high-speed buffer for the main DRAM.