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The SDRAM also maintains an internal counter, which iterates over all possible rows. The memory controller must simply issue a sufficient number of auto refresh commands (one per row, 8192 in the example we have been using) every refresh interval (t REF = 64 ms is a common value). All banks must be idle (closed, precharged) when this command is ...
For example, a system with 2 13 = 8,192 rows would require a staggered refresh rate of one row every 7.8 μs which is 64 ms divided by 8,192 rows. A few real-time systems refresh a portion of memory at a time determined by an external timer function that governs the operation of the rest of a system, such as the vertical blanking interval that ...
The storage cells on a memory chip are laid out in a rectangular array of rows and columns. The read process in DRAM is destructive and removes the charge on the memory cells in an entire row, so there is a column of specialized latches on the chip called sense amplifiers, one for each column of memory cells, to temporarily hold the data ...
Row Precharge Time T RP: The minimum number of clock cycles required between issuing the precharge command and opening the next row. The time to read the first bit of memory from a DRAM with the wrong row open is T RP + T RCD + CL. Row Active Time T RAS: The minimum number of clock cycles required between a row active command and issuing the ...
The memory cell is the fundamental building block of computer memory. The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 (high voltage level) and reset to store a logic 0 (low voltage level). Its value is maintained/stored until it is changed by the set/reset process.
A memory bank is a part of cache memory that is addressed consecutively in the total set of memory banks, i.e., when data item a(n) is stored in bank b, data item a(n + 1) is stored in bank b + 1. Cache memory is divided in banks to evade the effects of the bank cycle time (see above) [=> missing "bank cycle" definition, above]. When data is ...
DDR memory bus width per channel is 64 bits (72 for ECC memory). Total module bit width is a product of bits per chip and number of chips. It also equals number of ranks (rows) multiplied by DDR memory bus width. Consequently, a module with a greater number of chips or using ×8 chips instead of ×4 will have more ranks.
The number of row address bits remains at 17, for a maximum of 128K rows (17 → 17). One more column address bit (C10) is added, allowing up to 8192 columns (1 KB pages) in ×4 chips (11 → 12). The least-significant three column-address bits (C0, C1, C2) are removed. All reads and writes must begin at a column address which is a multiple of ...