Explanation of some memory terms (bank ECC, etc.) -- reprinted

Memory: Bank

In the memory industry, banks have at least three meanings, so be sure to pay attention to them. 1. On the SDRAM memory module, "bank number" indicates the number of physical storage bodies of the memory. (Equivalent to "row"/row) 2. The Bank also indicates the number of logical repositories in a SDRAM device. (Usually four banks ). 3. It also indicates the dimm or Simm connection slot or slot group, such as bank 1 or Bank. The bank here is the computing unit (also called the memory library) of the memory slot. It is the basic unit of work for the data bus between the computer system and the memory. The computer can start up normally only when one bank is fully inserted. For example, on the Pentium series motherboard, one 168 wire slot is a bank, and two 72 wire slots can constitute a bank. Therefore, the 72-wire memory must be paired. The reason is that the data width of the 168-line memory is 64-bit, while that of the 72-line memory is 32-bit. The bank number on the Main Board starts from bank0 and must be filled with bank0 before it can be started. The slots after bank1 will be used to upgrade and expand memory in the future, which is called the memory expansion slot. 　ECC is short for "error checking and correcting". The Chinese name is "error check and correction ". ECC is a technology that can realize "error check and correction". ECC memory is the memory that applies this technology. It is generally used on servers and graphics workstations, this will make the entire computer system more secure and stable at work. To learn more about ECC technology, you cannot skip to parity (parity ). Before the emergence of ECC technology, the most widely used technology in memory was parity (parity ). We know that in a digital circuit, the smallest data unit is bit, also called bit. Bit is also the smallest unit in memory, it uses "1" and "0" to indicate high and low level signals of data. In a digital circuit, eight consecutive bits are one byte, and each byte in the memory without "parity" is only eight bits, if an error occurs in the storage of one of its buckets, the corresponding data stored in the bucket will change, resulting in an application error. In addition, each byte (8 bits) exists in the "parity" field, and an additional bit is added for error detection. For example, a certain number (1, 0, 1, 0, 1, 0, 0, 1, and 1) is stored in a byte ), add up each phase (1 + 0 + 1 + 0 + 1 + 0 + 1 + 1 + 1 = 5 ). If the result is an odd number, the parity bit is defined as 1 for the even check, and the reverse is 0 for the odd check. When the CPU returns the read data, it will add the data stored in the first eight bits, and check whether the calculation result is consistent with the check bits. When the CPU finds that the two are not at the same time, it will make a view to correct these errors, but the parity has a disadvantage. When the memory finds a data bit error, it may not be able to determine the location, the error may not be corrected. Therefore, the main function of the memory with parity check is to "detect errors" and correct some simple errors. Through the above analysis, we know that the parity Memory checks the correctness of the current 8-bit data by adding a data bit based on the original data bit, however, as the number of data bits increases, the number of data bits that parity is used to test also doubles. That is to say, when the number of data bits is 16 bits, it needs to add two bits for check, when the data bit is 32 bits, four bits need to be added, and so on. Especially when the data volume is very large, the probability of data errors increases. The parity check method that can only correct simple errors does not work. It is based on this situation that, A new memory technology was born with an answer. This is ECC (error check and correction). This technology is also implemented by adding a verification bit to the original data bit. The difference is that the two methods are different, which leads to the different main functions of the two. It differs from parity in that if the data bit is 8 bits, an increase of 5 bits are required for ECC error check and correction. Each time the data bit is doubled, ECC only adds one bits, that is to say, when the data bit is 16 bits, the ECC bit is 6 bits, 32 bits are 7 bits, and the data bit is 64 bits, the ECC bit is 8 bits, and so on, each time the data bit doubles, only one ECC bit is added. In short, ECC can allow errors in the memory and correct errors so that the system can continue normal operations without interruption due to errors, and ECC can automatically correct errors, you can locate the error bits that cannot be checked by parity and correct the errors. At present, some manufacturers usually use sd ram for general PC low-end servers without ECC. 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