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Memory Memory technologies Static RAM (SRAM): Flip-Flops –Fast, expensive, used for caches Dynamic RAM (DRAM): Charge stored in capacitor –Leackage requires.

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Presentation on theme: "Memory Memory technologies Static RAM (SRAM): Flip-Flops –Fast, expensive, used for caches Dynamic RAM (DRAM): Charge stored in capacitor –Leackage requires."— Presentation transcript:

1 Memory Memory technologies Static RAM (SRAM): Flip-Flops –Fast, expensive, used for caches Dynamic RAM (DRAM): Charge stored in capacitor –Leackage requires periodic refreshing (< 2ms), slower –High density, cheap and used for main memory. EPROM, EEPROM: Charge stored in an isolated gate Storage of charge with high voltage Erase: via ultraviolet light (EPROM), or electrically (EEPROM, Flash ROM) Non-volatile memory PROM: Burning of fuses ROM: contents inserted during production

2 DRAM cell Architecture of a DRAM cell Read destroys information, therefore it has to be written back. Cycle time (time between two accesses) is larger than access time.

3 Architecture of a DRAM Chip

4 Memory Organization of PCs SDRAM (Synchronous DRAM) Synchron: All signals (RAS, Adresse …) are combined with a fixed clock cycle (PC100, PC133 …). Access via North Bridge or an integrated memory controller Prozessor Chip Satz (North Bridge) DIMM 1 or 2 rows Chip Select Address Data Control Data width is 64 Bit oder 8 Bytes Chip Select determines the row The row provides 8 Bytes Frontside Bus

5 Memory Organization of PCs Each row of a DIMM has 8 chips. To provide 1 GB per row we use eight 1 Gbit SDRAM chips. Each chip 8 data wires internally organized in 4 banks with 256 Mbit. Each bank is organized in eight memory arrays.

6 Internal Organization of a GBit DRAM 1 GBit or 128 MByte chips 128 M = adress lines 11 (2K) column 14 (16K) row 2 (4) memory field 16K rows, 2K columns 8 Bit width 1 Bit width

7 Access to DDR-SDRAM Read, Burst length=8 Burst Mode: transmission of 8 Bytes DDR (Double Data Rate): Transmission with rising and falling edge of the clock signal RAS-to-CAS-Delay (t RCD ), CAS latency (t CL ), RAS-to-Precharge- Latency (t RAS ), Read-Cycle-time (t RC ) Precharge necessary because of differential lines

8 Access to DDR-SDRAM, Page Hit Read, Burst length=8, Page Hit Page: Data in the amplifiers of a row All amplifiers of all blocks in the same bank Hit: Data from the same row are accessed.

9 Access to DDR-SDRAM, Bank Overlap Access to another bank can already start when the first burst is trasmitted.

10 Example Configuration Prozessor i875P Frontside Bus (FSB800) 200 MHz Quadpumped 4*64 Bit  6,4 GB/s DIMM (DDR400 chips) DIMM (PC3200) 3,2GB/s DIMM DIMM (PC3200) DDR MHz 400 MB/s Zwei Kanäle mit je 3,2 GB/s

11 RAMBUS Rambus DRAM (RDRAM) is internally very similar to DDR SDRAM.RambusRDRAM A point-to-point channel with higher clock rate and less pins in the memory controller is used. Since Intel switched in 2003 to DDR RAM, RAMBUS was almost eliminated. XDR-DRAM is used in the Sony PlayStation 3 XDR2-DRAM is used in high-end graphics cards and 3D TVs. 12,8 GBytes/s bandwidth

12 Static Memory One bit is implemented by 6 MOSFET transistors No refresh Very fast access times. Expensive compared to DRAM Used for caches

13 FLASH Memories Write A high voltage (10-13V) between gate and source lets electrons tunnel into the floating gate. Read The charge of the floating gate partially cancels the electric field from the control gate. Thus, a higher voltage is required to make the channel conduct. With a certain threshold voltage, the state of the transistor can be sensed. High negative voltage removes the charge Reset is done for 16 KB blocks. Isolation is damaged by reset.

14 NOR vs NAND NAND more compact since less wires, although more transistors read: offset power for other FETs NOR

15 Single and Multi Level Cells (SLC / MLC) SLCs store one bit MLCs store up to four bits Instead of only checking the presence of the current, the strenght is sensed. Thus, more presice measurement is required. The states are determined by the amount of charge in the floating gate. Thus, precise control of the charge deposit is required. Higher density, lower cost Larger bit error ratio Lower write speeds, lower number of program-erase cycles and higher power consumption

16 NAND Flash Performance Organized in pages (512 or 2048 bytes) Writes are performed to entire pages µs Reset done in larger blocks 1-2 ms Reads are fast 25 µs for 4KB

17 NAND Flash Durability – writes for each cell Solution Wear leveling: distribution of writes to same address over multiple cells. Spare cells

18 FLASH Usage Solid State Disc (SSD) Up to 512 GB (300 €), 1TB (800 €) Up to 520 MB/s Lesen und 400 MB/s Schreiben Lower energy consumtion in idle and active mode as normal discs Comparison with HDD see resources in Mindmap Hybrid Disc Nonvolatile buffer for write accesses Or used as permanent cache controlled by the OS Turbo Speicher PCIe-MiniCard from Intel to speedup boot process.


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