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Embedded DRAM (eDRAM) isdynamic random-access memory (DRAM) integrated on the samedie ormulti-chip module (MCM)[1] of anapplication-specific integrated circuit (ASIC) ormicroprocessor. eDRAM's cost-per-bit is higher when compared to equivalent standalone DRAM chips used as external memory, but the performance advantages of placing eDRAM onto the same chip as the processor outweigh the cost disadvantages in many applications. In performance and size, eDRAM is positioned betweenlevel 3 cache and conventional DRAM on the memory bus, and effectively functions as a level 4 cache, though architectural descriptions may not explicitly refer to it in those terms.
Embedding memory on the ASIC or processor allows for much widerbuses and higher operation speeds, and due to much higher density of DRAM in comparison toSRAM,[2] larger amounts of memory can be installed on smaller chips if eDRAM is used instead ofeSRAM. eDRAM requires additional fab process steps compared with embedded SRAM, which raises cost, but the area savings of eDRAM memory offsets the process cost when a significant amount of memory is used in the design.
eDRAM memories, like all DRAM memories, require periodic refreshing of the memory cells, which adds complexity. However, if the memory refresh controller is embedded along with the eDRAM memory, the remainder of the ASIC can treat the memory like a simple SRAM type, such as in1T-SRAM.
eDRAM is used in various products, includingIBM'sPOWER7 processor,[3] and IBM'sz15 mainframe processor (mainframes built which use up to 4.69 GB of eDRAM when 5 such add-on chips/drawers are used but all other levels from L1 up also use eDRAM, for a total of 6.4 GB of eDRAM).Intel'sHaswell CPUs with GT3e integrated graphics,[4] manygame consoles and other devices, such asSony'sPlayStation 2, Sony'sPlayStation Portable,Nintendo'sGameCube, Nintendo'sWii, Nintendo'sWii U, and Microsoft'sXbox 360 also use eDRAM.[citation needed]
| Product name | Amount of eDRAM |
|---|---|
| IBMz15 | 256+ MB |
| IBM's System Controller (SC) SCM, with L4 cache for the z15 | 960 MB |
| IntelHaswell, Iris Pro Graphics 5200 (GT3e) | 128 MB |
| IntelBroadwell, Iris Pro Graphics 6200 (GT3e) | 128 MB |
| IntelSkylake, Iris Graphics 540 and 550 (GT3e) | 64 MB |
| Intel Skylake, Iris Pro Graphics 580 (GT4e) | 64 or 128 MB |
| IntelCoffee Lake, Iris Plus Graphics 655 (GT3e) | 128 MB |
| PlayStation 2 | 4 MB (as aframebuffer) |
| PlayStation Portable | 2 MB (for theMedia Engine) |
| 2 MB (for theGPU) | |
| Xbox 360 | 10 MB |
| Wii U | 32 MB |