Bic10503 Computer Architecture Chapter 3 PDF

BIC10503 Computer Architecture CHAPTER 3 MEMORY ORGANIZATION 3.2 Internal memory  Organization  The basic element of a semiconductor memory is the memory cell.  Although a variety of electronic technologies are used,...

BIC10503 Computer Architecture CHAPTER 3 MEMORY ORGANIZATION 3.2 Internal memory  Organization  The basic element of a semiconductor memory is the memory cell.  Although a variety of electronic technologies are used, all semiconductor memory cells share certain properties:  They exhibit two stable (or semi-stable) states, which can be used to represent binary 1 and 0.  They are capable of being written into (at least once), to set the state.  They are capable of being read to sense the state. Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 2  Memory Cell Operation Indicate read/write Select memory cell Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 3  Semiconductor Memory Types Memory Type Category Erasure Write Mechanism Volatility Random-access memory (RAM) Read-write memory Electrically, byte-level Electrically Volatile Read-only memory (ROM) Masks Read-only memory Not possible Programmable ROM (PROM) Erasable PROM (EPROM) UV light, chip-level Nonvolatile Electrically Electrically Erasable Read-mostly memory PROM (EEPROM) Electrically, byte-level Flash memory Electrically, block-level Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 4 Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 5  Semiconductor Memory  RAM (Random Access Memory)  Two basic types of RAM Memory chips that can be read from and written chips : SRAM & DRAM  SRAM to by processor Most RAM is (Static Random Access Memory) Also called volatile, it is lost  DRAM main memory when computer’s or primary power is (Dynamic Random Access Memory) storage turned off *temporary storage The more RAM a computer has, the faster it responds Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 6 Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 7  Dynamic RAM  Bits stored as charge in capacitors  Charges leak ◦ tendency of the stored charge to leak away, even with power continuously applied; without being refreshed the stored data would eventually be lost Note: In electronics, leakage may refer to a gradual loss of energy from a charged capacitor.  Need refreshing even when powered  Simpler construction  Smaller per bit  Need refresh circuits  Essentially analogue ◦ Level of charge determines value Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 8  Static RAM  Bits stored as on/off switches  No charges to leak  No refreshing needed when powered  More complex construction  Larger per bit  Does not need refresh circuits  Digital ◦ Uses flip-flops Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 9 Differences  Uses bi-stable latching  Stores each bit of data circuitry to store each in a separate bit (flip flop). capacitor within an  Size: 1MB to 16MB integrated circuit.  Size: 1GB to 16GB SRAM DRAM 10 Differences  Static  Dynamic  Faster  Slower  Low power  High power consumption consumption  More transistors  Less transistors  Cheap  Expensive  Used as main memory  Used as cache e.g. L1, L2, L3 caches SRAM DRAM 11  Read Only Memory (ROM)  Permanent storage ◦ Nonvolatile ◦ a permanent pattern of data that cannot be changed.  Microprogramming (refer textbook)  Library subroutines  Systems programs (BIOS)  Function tables Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 12  A ROM is created like any other integrated circuit chip, with the data actually wired into the chip as part of the fabrication process. Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 13  Types of ROM  Written during manufacture ◦ Very expensive for small runs  Programmable (once) = PROM ◦ Needs special equipment to program ◦ Blank ROM chip onto which a programmer can write permanently ◦ PROM chips have several different applications, including cell phones, video game consoles, RFID tags, medical devices, and other electronics.  Read “mostly” ◦ Erasable Programmable (EPROM)  Erased by UV ◦ Electrically Erasable (EEPROM)  Takes much longer to write than read ◦ Flash memory  Erase whole memory electrically Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 14  Refreshing  Refresh circuit included on chip  Disable chip  Count through rows  Read & Write back  Takes time  Slows down apparent performance Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 15  Interleaved Memory  Collection of DRAM chips  Grouped into memory bank  Banks independently service read or write requests  K banks can service k requests simultaneously Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 16  Error Correction  Hard Failure ◦ Permanent defect  Soft Error ◦ Random, non-destructive ◦ No permanent damage to memory  Detected using Hamming error correcting code Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 17  Error Correcting Code (ECC) Function The comparison yields one of three results: No errors are detected. The fetched data bits are sent out. An error is detected, and it is possible to correct the error. The data bits plus error correction bits are fed into a corrector, which produces a corrected set of Mbits to be sent out. calculation, depicted as a An error is detected, but it is not possible function f, is performed to correct it.This condition is reported. Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 18  Hamming Error-Correcting Code Each parity bit is chosen so that the total number in its circle is even Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 19  Advanced DRAM Organization  Basic DRAM same since first RAM chips  Enhanced DRAM ◦ Contains small SRAM as well ◦ SRAM holds last line read (c.f. Cache!)  Cache DRAM ◦ Larger SRAM component ◦ Use as cache or serial buffer Performance Comparison of Some DRAM Alternatives Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 20  Synchronous DRAM (SDRAM)  Access is synchronized with an external clock  Address is presented to RAM  RAM finds data (CPU waits in conventional DRAM)  Since SDRAM moves data in time with system clock, CPU knows when data will be ready  CPU does not have to wait, it can do something else  Burst mode allows SDRAM to set up stream of data and fire it out in block  DDR-SDRAM sends data twice per clock cycle (leading & trailing edge) Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 21  SDRAM Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 22  RAMBUS  A memory subsystem designed to transfer data at faster rates.  RDRAM is made up of a random access memory (RAM), a RAM controller and a bus path that connect RAM to microprocessors and other PC devices.  Example of applications: game consoles Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 23  RAMBUS  Adopted by Intel for Pentium & Itanium  Main competitor to SDRAM  Vertical package – all pins on one side  Data exchange over 28 wires < cm long  Bus addresses up to 320 RDRAM chips at 1.6Gbps  Asynchronous block protocol ◦ 480ns access time ◦ Then 1.6 Gbps Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 24  RAMBUS Diagram Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 25  DDR SDRAM  SDRAM can only send data once per clock  Double-data-rate (DDR) SDRAM can send data twice per clock cycle ◦ Rising edge and falling edge Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 26  Cache DRAM  Mitsubishi  Integrates small SRAM cache (16 kb) onto generic DRAM chip  Used as true cache ◦ 64-bit lines ◦ Effective for ordinary random access  To support serial access of block of data ◦ E.g. refresh bit-mapped screen  CDRAM can prefetch data from DRAM into SRAM buffer  Subsequent accesses solely to SRAM Fakulti Sains Komputer dan Technology Maklumat (FSKTM), UTHM 27 Thank You Q&A