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COMPUTER ARCHITECTURE (P175B125) Assoc.Prof. Stasys Maciulevičius Computer Dept.
©S.Maciulevičius Virtual memory Modern computers can simultaneously run several programs (in parallel or pseudoparallel mode) Each such program (process) has a separate code and data area The mechanism that provides for more processes run simultaneously, sharing the memory correctly and correct addresing of information, transforming logical addresses to physical addresses is called Virtual Memory
©S.Maciulevičius Virtual memory Moreover, the virtual memory ensure that the necessary for process information (program code and data) at the appropriate time would be loaded in the main memory, protects the process memory space from other processes Virtual memory in physical point of view - the main memory plus part of the external memory, together with the tools for address transforming and information interchanging between these levels Virtual memory in logical point of view - extended memory space with contiguous addressing
©S.Maciulevičius Virtual memory There are two main principles used in realization of virtual memory: 1)Segmentation - an application's virtual address space is divided into variable-length segments. A virtual address consists of a segment number and an offset within the segment. Task may have several segments – code (program), data, stack. 2)Paging – an application's virtual address space is divided into fixed sized pages; a page is a block of contiguous virtual memory addresses, usually at least 4Kbytes in size. The pages do not have to be contiguous in memory
©S.Maciulevičius Main and external memory CPU reg. Swap in segment (page) Cache Main memory External memory Swap out segment (page)
©S.Maciulevičius Segmented virtual memory Op. system 1’st process 2’nd process 3’rd process 4’th process 5’th process Op. system 2’nd process 3’rd process 4’th process 5’th process Op. system 2’nd process 3’rd process 5’th process Op. system 2’nd process 3’rd process 6’th process 5’th process
©S.Maciulevičius Segmenting Segment No.Byte address Segm.No. 32-bit base H 1 4F000H H … …. Memory 2 segm 0 segm. 1 segm Segment table 4F
©S.Maciulevičius Simple mechanism of segmentation Stack length Data length Program length MUX Stack base Data base Program base MUX Page fault Compa- rator Offset Segment Sum- mator Physical address
©S.Maciulevičius Segmentation principles in IA-32 SelectorEffective address Descriptor table Segment descriptor + Base address Linear (physical) address 31 0
©S.Maciulevičius Segmentation mechanism in IA-32 In IA-32 architecture segmentation is supported by folowing tools: mechanism for calculation of physical address segment descriptor tables: local descriptor table (LDT) global descriptor table (GDT) interrupt descriptor table (IDT) privilegy system Each table has assigned to it the processor register, which holds: 16-bit limit (size of table) 32-bit base address (table location in memory)
©S.Maciulevičius Address spaces in IA-32 IA-32 architecture has three such address spaces: logical address space; logical (or virtual) address consists of two integers: a 16-bit segment selector and a 32-bit offset; space size is 2 14 selectors 4 GB = 64 TB linear address space; linear address appears on the output of segmentation unit, as result of logical address translation; physical address space; physical address appears on the output of paging unit; in case when paging is not used, physical address equals to linear address; this address (BE7-BE0 bits and A31-A3) goas to main memory
©S.Maciulevičius Simple mechanism of paging Page table Logical page number Byte offset Page frame number Byte offset Protection bits
©S.Maciulevičius Segmentation with paging in IA-32 SelectorEffective address (offset) Segmentation unit Physical address 31 0 Descriptor’s index Paging unit (optional) Linear address
©S.Maciulevičius Segmentation mechanism in IA-32
©S.Maciulevičius Paging in IA-32 Page table Directory Page No. Byte offset Linear address Page directory PDE PTE Page (4 KB) Target CR3 (PDBR) Control register ( Page Directory Phys. Base Address )
©S.Maciulevičius Address translation Transformation of virtual address to physical is address translation. The problem - the extra step – access to page table. How to speed up the memory access? 1.To store whole page table in processor - is unrealistic because the page table takes a lot of place - megabytes. For example, if the page size is 4 KB, a 4 GB of memory takes 4 GB / 4 KB = 1024 K pages! 2.To store part of page table in special cache in processor. Each entry in this cache ensure fast access even to 1000 words
©S.Maciulevičius Translation lookaside buffer (TLB) Page table Logical page number Byte offset Page frame number Byte offset TLB OR Page not in main memory Effective address from CPU Miss Load TLB Hit Page swap with hard disc Physical address to main memory
©S.Maciulevičius TLB and cache Physical address TagTag Byte No. Hit Data line Logical page number Byte offset Cache Effective address =? ByteByte TLB Index
©S.Maciulevičius Memory management unit A memory management unit (MMU) is a computer hardware component responsible for handling accesses to memory requested by the CPU Its functions include: translation of virtual addresses to physical addresses (i.e., virtual memory management) memory protection cache control bus arbitration, and, in simpler computer architectures (especially 8-bit systems) bank switching
©S.Maciulevičius AMD K7 microarchitecture
©S.Maciulevičius Parity checking A parity checking refers to the use of parity bits to check that data has been writted and readed accurately The parity bit is added to every data unit (typically byte) The parity bit for each unit is set so that: unit has either an odd number or unit has an even number of set bits
©S.Maciulevičius Parity checking k = b 0 b 1 … b 7 or k = 1 b 0 b 1 … b k Data bus Error Data bus Usually k=n/8 n k k n Address bus 1 Data AR bytes DR generating parity bits / checking n m Parity bits
©S.Maciulevičius Error-checking and correcting Hamming code: a error-correcting code, can detect up to two simultaneous bit errors, and correct single-bit errors Code length usually is k=log 2 n + 1; With additional parity - k=log 2 n + 2 Data bus Error n k k n Address bus 1 Data AR bytes DR Generating of Hamming code k m ECC bits Hamming check Error Correc- tion k n n
©S.Maciulevičius Hamming code Bit Binary Contr. Data D D D D K D D D K D K K1 Hamming code detects up to two simultaneous bit errors, and corrects single-bit errors
©S.Maciulevičius Generating of Hamming code K1 = D1 D2 D4 D5 D7 K2 = D1 D3 D4 D6 D7 K4 = D2 D3 D4 D8 K8 = D5 D6 D7 D8 Let data byte is , bit D1 – at right. Then: K1 = 1 0 1 1 0 = 1 K2 = 1 0 1 1 0 = 1 K4 = 0 0 1 0 = 1 K8 = 1 1 0 0 = 0 Data byte is saved im memory with control bits:
©S.Maciulevičius Error correction Let error occus, e.g., instead: we have Calculate Hamming code: K1 = 1 0 1 1 0 = 1 K2 = 1 1 1 1 0 = 0 K4 = 0 1 1 0 = 0 K8 = 1 1 0 0 = 0 Use sum mod2: K8 K4 K2 K – this is number of fault bit
©S.Maciulevičius Error correction : redundancy Single error correction Single error correction, double error detection Data bits ECC bits Redun- dancy, % ECC bitsRedundancy, % 8450,00562, ,25637, ,75721, ,4812, ,2597, ,52103,91
©S.Maciulevičius External memory As long-term storage in computers are used: hard drives CD-ROM, CDs (optical compact discs) DVDs flash memory floppy disks (outdated) strimmers.
©S.Maciulevičius External memory
©S.Maciulevičius External memory Access modes: direct access sequential access Parameters: capacity access time data transfer spped relative price
©S.Maciulevičius First HD IBM announced the IBM 350 storage unit as a component of the RAMAC 305 computer system on September 13, 1956 Assembled with covers, the 350 was 60 inches long, 68 inches high and 29 inches deep It was configured with 50 magnetic disks containing 50,000 sectors, each of which held 100 alphanumeric characters, for a capacity of 5 million characters
©S.Maciulevičius First HD 50 platters 1 head
©S.Maciulevičius First HD Disks rotated at 1,200 rpm ; tracks (20 to the inch) were recorded at up to 100 bits per inch, and typical head-to-disk spacing was 800 microinches The execution of a "seek" instruction positioned a read-write head to the track that contained the desired sector and selected the sector for a later read or write operation Seek time averaged about 600 milliseconds
©S.Maciulevičius Hard disk drive
©S.Maciulevičius Hard disk drive Platters vary in size and hard disk drives come in two form factors, 5.25in or 3.5in Typically two or three or more platters are stacked on top of each other with a common spindle Tthe head flies a fraction of a millimetre above the disk. On early hard disk drives this distance was around 0.2mm. In modern-day drives this has been reduced to 0.07mm or less There's a read/write head for each side of each platter, mounted on arms
©S.Maciulevičius Hard disk drive The disk controller controls the drive's servo- motors and translates the fluctuating voltages from the head into digital data for the CPU More often than not, the next set of data to be read is sequentially located on the disk. For this reason, hard drives contain between 256KB and 8MB of cache buffer in which to store all the information in a sector or cylinder in case it's needed. This is very effective in speeding up both throughput and access times
©S.Maciulevičius Technical specifications Capacity: Amount of data which can be stored on a hard drive Transfer rate: Quantity of data which can be read or written from the disk per unit of time. It is expressed in bits per second (Mb/s) Rotational speed: The speed at which the platters turn, expressed in rotations per minute (rpm for short). Hard drive speeds are on the order of 7200 to rpm. The faster a drive rotates, the higher its transfer rate. On the other hand, a hard drive which rotates quickly tends to be louder and heats up more easily
©S.Maciulevičius Technical specifications Latency (also called rotational delay): The length of time that passes between the moment when the disk finds the track and the moment it finds the data Average access time: Average amount of time it takes the read head to find the right track and access the data. In other words, it represents the average length of time it takes the disk to provide data after having received the order to do so. It must be as short as possible Radial density: number of tracks per inch (tpi). Linear density: number of bits per inch (bpi) on a given track. Surface density: ratio between the linear density and radial density (expressed in bits per square inch).
©S.Maciulevičius Technical specifications Cache memory: Amound of memory located on the hard drive. Cache memory is used to store the drive's most frequently-accessed data, in order to improve overall performance Interface: the connections used by the hard drive. The main hard drive interfaces are IDE/ATA, SATA, SCSI
©S.Maciulevičius Information on disk
©S.Maciulevičius Information on disk The data is organised in concentric circles called "tracks" The tracks are separated into areas called sectors, containing data (generally at least 512 octets per sector) The term cylinder refers to all data found on the same track of different platters The term clusters (also called allocation units) refers to minimum area that a file can take up on the hard drive
©S.Maciulevičius Hard disk Formatted and unformatted disk capacity Capacity = Number_of_cylinders Number_of_surfaces Number_of_sectors/cilinder sector_size Modern disk capacity is at least 500 GB, advanced disks even reach 4 TB
©S.Maciulevičius Hard disk Access time depends on the following parameters: cylinder seek time delay on the rotation transfer time Information transmission time depends on: recording density and disk rotational speed
©S.Maciulevičius Old disk - MD Maxtor 33073H3 Capacity30 GB Integrated interfaceATA-5 / Ultra ATA/100 Buffer size/ type2 MB SDRAM Surfaces / Heads3 Platters2 Arreal density14.7 Gb / sq. in. max Track density tpi Linear density kb/colyje Bytes per sector/ Block512 Sectors in track Sectors in disk
©S.Maciulevičius Old disk - MD Maxtor 33073H3 Seek time (read op.) Track-track1.0 ms Average9.5 ms Rotational speed(+ 0.1%)5400 RPM Data transfer rate To/from interface (Ultra ATA/100, DMA M5) to 100 MB/s. To/from interface (PIO 4 / Multi-word DMA M5) to 16.7 MB/s To/from mediumto 46.7 MB/s Start time8.5 s
©S.Maciulevičius Recording methods Traditional recording method –horizontal recording: N S S N N SS NN S Now a new recording method is in use – vertical (perpendicular) recording. The bits are in a vertical arrangement instead of horizontal in order to take up less space. By 2010, perpendicular densities are expected to exceed 500 Gb/sq. in. NSNS SNSN SNSN NSNS SNSN SNSN SNSN NSNS SNSN NSNS
©S.Maciulevičius Disk density Disk Density is measured and is also called areal density Now how is this density calculated? For the most part the density we measure in Bit per Inch (BPI) and track per inch (TPI) When we multiply the TPI and BPI we get areal density RAMAC had an areal density of 2,000 bit/in²
©S.Maciulevičius Disk density In 2012 the highest areal density was around 625Gb/inch 2. HDD areal densities measuring data-storage capacities are projected to climb to a maximum 1800Gb/inch 2 per platter by 2016, up from 744Gb/inch 2 in 2011, as shown in the figure below This means that from 2011 to 2016, the five-year compound annual growth rate (CAGR) for HDD areal densities will be equivalent to 19% For this year, HDD areal densities are estimated to reach 780Gb/inch 2 per platter, and then rise to 900Gb/inch 2 next year.
©S.Maciulevičius Disk density
©S.Maciulevičius Disk capacity
©S.Maciulevičius Flash memory Flash memory refers to a particular type of EEPROM (Electronically Erasable Programmable Read Only Memory). It is a memory chip that maintains stored information without requiring a power source Flash memory differs from EEPROM in that EEPROM erases its content one byte at a time. This makes it slow to update. Flash memory can erase its data in entire blocks, making it a preferable technology for applications that require frequent updating of large amounts of data
©S.Maciulevičius Flash memory Flash memory combines several useful features: high packing density (the cell is 30% smaller than the DRAM) maintaining stored information without requiring a power supply erasing and recording information using electrical signals low energy consumption high reliability and low price
©S.Maciulevičius Flash memory Flash memory is used primarily as: rarely rewritten (eg, BIOS) memory compact exchangeable memory in computers (USB keys) compact exchangeable memory in PDAs, digital cameras, digital audio players etc. E.g., Kingston DataTraveler 200 is 32GB-128GB capacity (DataTraveler 300 – 256GB), has 20MB/sec read, 10MB/sec write speed DataTraveler Vault has 256-AES hardware-based encryption, 2GB-32GB capacity
©S.Maciulevičius Solid state memory Solid state memory or a solid state drive (SSD) is a device that uses no moving parts to store data The first ferrite memory SSD devices, or auxiliary memory units as they were called at the time, emerged during the era of vacuum tube computers In the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of IBM, Amdahl and Cray; however, the high price of the SSDs made them quite seldom used RAM "disks" were popular as boot media in the 1980s when hard drives were expensive, floppy drives were slow
©S.Maciulevičius Solid state memory 2004: Texas Memory Systems' RamSan-325 can carry out 250,000 I/O operations a second. Available in capacities of 128, 96, 64, and 32 gigabytes, RamSan-325 accelerates I/O intensive applications by delivering random data at sustained rates exceeding 1.5 Gbps Non-volatile product has high availability architecture with redundant and hot swappable power supplies, redundant batteries However, build using 512Mb of DDR RAMs, device was quite expensiv – 16 GB device costs $36.000
©S.Maciulevičius Solid state memory Now fash memory is media for building solid state memory devices These devices can range up to 512GB (or even more) Flash memory used as a hard drive has many advantages over a traditional hard drive It is silent, much smaller than a traditional hard drive, and highly portable with a much faster access time However, the advantages of a traditional hard drive are price and capacity
©S.Maciulevičius SSD Most SSD manufacturers use non-volatile flash memory to create more compact devices for the consumer market These flash memory-based SSDs, also known as flash drives, do not require batteries. They are often packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch) In addition, non-volatility allows flash SSDs to retain memory even during sudden power outages, ensuring data persistence Flash memory SSDs are slower than DRAM SSDs and some designs are slower than even traditional HDDs on large files, but flash SSDs have no moving parts and thus seek times and other delays inherent in conventional electro-mechanical disks are negligible
©S.Maciulevičius SSD prices – some facts In March 2007 SanDisk announced it was offering its 32GB 2.5" SATA SSD to oems for $350. In July 2008 OCZ said its fast Core series 2.5" SSDs were available with an price of $169 for 32GB October 2009: Active Media Products launched its Aviator 312 line of bus powered fast USB 3.0 external SSDs with R/W speeds upto 240MB/s and 160MB/s respectively. Capacity options include:- 16GB ($89), 32GB ($119) and 64GB ($209) 2013: Kingston SSDNow V300 Series SV300S37A/120G 2.5" 120GB SATA III Internal SSD - $ SanDisk Extreme SDSSDX-480G-G25 2.5" 480GB SATA III SSD - $369.99
©S.Maciulevičius SSD and HD
©S.Maciulevičius Hybrid hard drive Certain technology meets half-way between hard drive and solid-state drive, such as the hybrid drive, and ReadyBoost A hybrid drive, sometimes called hybrid hard drive, uses a small SSD as a cache. The SSD is often flash memory ReadyBoost is a part of the Microsoft Windows Vista operating system that uses compatible flash memory as a drive for a disk cache A random disk read from the cache is generally 80 to 100 times faster than random disk read from a traditional hard drive
Hybrid hard drive Controller Flash memory Hard disk Interface Cache controller Hybrid drive S.Maciulevičius 61
©S.Maciulevičius Solid State Hybrid Drives
©S.Maciulevičius Adaptive Memory™ technology Adaptive Memory™ technology from Seagate selectively tackles data that is frequently read and time–consuming to fetch. Seagate SSHD drives can then copy this data into the flash Adaptive Memory technology makes such efficient use of the drive’s solid state memory that only 4GB to 8GB of flash capacity is actually needed. This reduces costs so much that it’s now practical to employ enterprise-class SLC NAND flash memory, the fastest and most reliable type of flash memory on the market
©S.Maciulevičius Intel Smart Response Technology Smart Response Technology (SRT) is a proprietary caching mechanism introduced in 2011 by Intel for their Z68 chipset (for the Sandy Bridge–series processors), which allows a SATA solid-state drive (SSD) to function as cache for a (conventional, magnetic) hard disk drive This provides the advantage of having a hard disk drive (or a RAID volume) for maximum storage capacity while delivering an SSD-like overall system performance experience
©S.Maciulevičius Intel Smart Response Technology Time To RunCold BootUnigineFallout 3Photoshop Elements) No SSD Cache 28 sec40 sec13 sec19 sec SSD Cache - Pass 1 23 sec35 sec13 sec19 sec SSD Cache - Pass 2 18 sec24 sec8 sec19 sec SSD Cache - Pass 3 16 sec24 sec7 sec18 sec SSD Cache - Pass 4 15 sec24 sec7 sec18 sec
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