Memory Organisation And Random Access Memory Computer Science Essay

store Organisation And stochastic Access remembering recordy reck geniusr Science Essay keeping stores, instructions and data. retrospect is of deuce types, capital remembrance board and secondary coil depot board. Instruction or data devoted by input devices is first pop offting stored in the primary store. tho user saves processed ( consortd) data in the secondary retentiveness. Primary storage is temporary and secondary computer store is permanent.Primary memory is the main memory of the computer ashes. It is high-speed than secondary memory. It directly communicates with processor.3.2 Memory UnitComputer uses several types of memories to save instructions and data. Computer uses beat and fixed storage as primary memory.RAM is a primary memory utilise in the computer. It is volatile since its content is accessible only as long as the computer is ON. The content of RAM is cle bed as soon as computer is powered OFF. SRAM is utilise as cache memory in the computer arrangement. A fluid drachm is used as main memory of the computer system. Types of DRAM are as SDRAM, DDRAM and RDRAM.ROM (Read Only Memory) is non-volatile read only memory unit. It used to store firmware, for example BIOS political program. holdr plunder only read content of the ROM, elicit not write or modify.A secondary memory is non-volatile. A devices used as secondary memory are HDD, FDD, CD, DVD, Tape drives and so on.FDD (Floppy Disk Drives) used as magnetic, portable memory device. It stores maximum 1.44 MB data. Earlier it used to transferral data among computer systems.HDD (Hard Disk Drives) are fixed, magnetic memory device. It is decisive in the computer system because user saves permanent data on the HDD. Storage capacity of HDD is vendor specific.CDs and DVDs are optical memory units used for transferring data and programs among the computers. CDs are situateable in the size 650MB, DVDs are available up to 4 GB in a size.Tape drives are normally used for data backup purpose.MemoryPrimary MemorySecondary MemoryRAMROMSRAMDDRAMSDRAMRDRAMPROMHDDDRAMerasable programmable read-only memoryEEPROMFDDCDDVDTape drivesFigure 3.1 Memory Types3.3 Memory pecking orderComputer system includes varies types of memories such as Primary memory, Secondary memory, memorialize drives and so on. These all memories are organised in hierarchy to get better performance. Memory hierarchy explains you that how computer system use memory while execution.Figure 3.3 shows Memory hierarchy. This hierarchy is made on the institution of few characteristics of memory, as listed followAccess Time Time interpreted by memory to read or write data.Memory size It amount of memory.Cost per byte it is m whiztary value required to access per byte.Transfer bandwidth It speed of the RAM.Unit of transfer entropy transfer rate.Increasing speed and cost per bit an decreasing sizeRegisters in CPULevel one cacheLevel two cacheMain memoryvirtual(prenominal) MemoryI ncreasing Size, decreasing speed and costcapacity stick storageFigure 3.3 Memory HierarchyMemory hierarchy is having CPUs prevalent purpose registers on the top. Register provides fastest data access and it is one of the most expensive memory location.Second and third levels are level-1 and level-2 cache respectively. The level one cache is small in size (4Kbytes to 32 Kbytes) though much larger than register. It is fixed on CPU verification so user send word not expand.The level-2 cache is present on some CPUs only. It is much larger than level one cache. User gage not expand it as it is fixed on CPU spot but it is less in cost than level one cache. realistic memory is part of record drive, which simulates to memory. Disk drives are less expensive so cost per bit is signifi send awaytly less.File storage is disk drive storage. It is bit slower.3.4 RAM (Random Access Memory )RAM is primary volatile memory unit so data will discharge in case of power failure. RAM access any me mory cell directly that why know as random access. RAM contains Operating System, application software and currently used data. Types of RAM cognize are as followsSRAM (Static Random Access Memory) SRAM is made with several transistors, usually four to six, for each memory cell. It does not require brush up fourth dimension as capacitors are not used. It is much faster than DRAM. Computer system use SRAM as cache memory.DRAM (Dynamic Random Access Memory) It has memory cells with a paired transistor it uses capacitor so need hebdomadal refresh. So it is lower than SRAM. DRAM is used as main memory in the computer system. As technology enhanced DRAM get also get enhanced from SDRAM then DDRAM to RDRAM..3.6 Read Only Memory (ROM)ROM is non-volatile primary memory. Data written on ROM can not delete or overwrite. Data is burned on the ROM as firmware. ROM memory is used in the computer system to write firmware for example BIOS program. Types of ROM are as followsProgrammable read -only memory (PROM) This type of memory is one cartridge clip written memory. Once program is written can not be change.Erasable programmable read-only memory (EPROM) Data written on EPROM can be erased. Ultraviolet is used to erase the data written on PROM.Electrically erasable programmable read-only memory (EEPROM) It is homogeneous as EPROM but to erase data solo it requires electrical signal. So not require to remove from computer. Data can be erased or over written it the computer itself.3.8 Cache MemoryThe cache is small amount of memory with high speed.Cache memory keeps data and code (introductions) that are used by CPU often.Use of cache memory reduced the waiting magazine of CPU that makes CPU more effective.SRAM is used to create cache memory. SRAM does not required refresh as it does not use capacitors as DRAM, it is 10 times faster than DRAM.Cache is of two types Level-1 that is hardened ion the CPU. Level 2 cache is ex gratia some processors have this type of m emory that is some time placed inside the CPU or placed near by CPU.To execute next instruction, CPU first check cache memory for the same instruction if that instruction is not available then it goes further.Note DRAM is made up of capacitors which need constant refreshing to preserve data. SRAM uses blow circuit that does not require refresh.3.8.1 Cache line replacement Algorithms epoch a new line is loaded in the cache, one of the alert lines must be replaced. Direct mapped cache, same block from line is aloof take place for new one. In associative cache, it can reckon for another place. Four of the most common line replacement algorithms are as followsLRU (Lease Recently Used) the cache line that was last referenced in the most distance bygone is replaced.FIFO (First In First Out) the cache line from the set that was loaded in the most distant past is replaced.LFU ( Least Frequently Used) the cache line that has been referenced the times is replaced.Random a randomly s elected line from cache is replaced.Note The most ordinarily used algorithm is LRU.Virtual MemoryOperating system enables host process through which space of hard disk drive can be simulate to RAM. The HDD space used as RAM is known a Virtual Memory.As cost per byte of HDD is less, virtual memory is right to run many large programs that need more memory.Access time of RAM is in nanoseconds but virtual memory gives access time in milliseconds. It is much slower than RAM.