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Embedded DRAM (eDRAM) is dynamic random-access memory (DRAM) integrated on the same dieormulti-chip module (MCM)[1] of an application-specific integrated circuit (ASIC) or microprocessor. 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 between level 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 wider buses and higher operation speeds, and due to much higher density of DRAM in comparison to SRAM,[citation needed] larger amounts of memory can be installed on smaller chips if eDRAM is used instead of eSRAM. eDRAM requires additional fab process steps compared with embedded SRAM, which raises cost, but the 3× 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 in 1T-SRAM.
eDRAM is used in various products, including IBM's POWER7 processor,[2] and IBM's z15 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's Haswell CPUs with GT3e integrated graphics,[3] many game consoles and other devices, such as Sony's PlayStation 2, Sony's PlayStation Portable, Nintendo's GameCube, Nintendo's Wii, Nintendo's Wii U, Apple Inc.'s iPhone, Microsoft's Zune HD, and Microsoft's Xbox 360 also use eDRAM.
| Product name | Amount of eDRAM |
|---|---|
| IBM z15 | 00256+ MB |
| IBM's System Controller (SC) SCM, with L4 cache for the z15 | 00960 MB |
| Intel Haswell, Iris Pro Graphics 5200 (GT3e) | 00128 MB |
| Intel Broadwell, Iris Pro Graphics 6200 (GT3e) | 00128 MB |
| Intel Skylake, Iris Graphics 540 and 550 (GT3e) | 00064 MB |
| Intel Skylake, Iris Pro Graphics 580 (GT4e) | 00064 or 128 MB |
| Intel Coffee Lake, Iris Plus Graphics 655 (GT3e) | 00128 MB |
| PlayStation 2 | 00004 MB |
| PlayStation Portable | 00004 MB |
| Xbox 360 | 00010 MB |
| Wii U | 00032 MB |
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Dynamic random-access memory (DRAM)
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