Chapter 5 & 6 Memory PDF

+ Chapter 5 Internal Memory + Dynamic RAM (DRAM) ◼ RAM technology is divided into two technologies: ◼ Dynamic RAM (DRAM) ◼ Static RAM (SRAM) ◼ DRAM ◼ Made with cells that store data as charge on capacitors ◼ Presence or absence of ch...

+ Chapter 5 Internal Memory + Dynamic RAM (DRAM) ◼ RAM technology is divided into two technologies: ◼ Dynamic RAM (DRAM) ◼ Static RAM (SRAM) ◼ DRAM ◼ Made with cells that store data as charge on capacitors ◼ Presence or absence of charge in a capacitor is interpreted as a binary 1 or 0 ◼ Requires periodic charge refreshing to maintain data storage ◼ The term dynamic refers to tendency of the stored charge to leak away, even with power continuously applied + Static RAM (SRAM) ▪ Digital device that uses the same logic elements used in the processor ▪ Binary values are stored using traditional flip-flop logic gate configurations ▪ Will hold its data as long as power is supplied to it  SRAM versus DRAM SRAM ◼ Both volatile ◼ Power must be continuously supplied to the memory to preserve the bit values ◼ Dynamic cell ◼ Simpler to build, smaller ◼ More dense (smaller cells = more cells per unit area) DRAM ◼ Less expensive ◼ Requires the supporting refresh circuitry ◼ Tend to be favored for large memory + requirements ◼ Used for main memory ◼ Static ◼ Faster ◼ Used for cache memory (both on and off chip) + Read Only Memory (ROM) ◼ Contains a permanent pattern of data that cannot be changed or added to ◼ No power source is required to maintain the bit values in memory ◼ Data or program is permanently in main memory and never needs to be loaded from a secondary storage device ◼ Data is actually wired into the chip as part of the fabrication process ◼ Disadvantages of this: ◼ No room for error, if one bit is wrong the whole batch of ROMs must be thrown out ◼ Data insertion step includes a relatively large fixed cost + Programmable ROM (PROM) ◼ Less expensive alternative ◼ Nonvolatile and may be written into only once ◼ Writing process is performed electrically and may be performed by supplier or customer at a time later than the original chip fabrication ◼ Special equipment is required for the writing process ◼ Provides flexibility and convenience ◼ Attractive for high volume production runs  Read-Mostly Memory Flash EPROM EEPROM Memory Electrically erasable programmable read-only Intermediate between Erasable programmable memory EPROM and EEPROM in read-only memory both cost and functionality Can be written into at any time without erasing prior contents Uses an electrical erasing Erasure process can be technology, does not performed repeatedly Combines the advantage of provide byte-level erasure non-volatility with the flexibility of being updatable in place More expensive than Microchip is organized so PROM but it has the that a section of memory advantage of the multiple More expensive than cells are erased in a single update capability EPROM action or “flash” + Error Correction ◼ Hard Failure ◼ Permanent physical defect ◼ Memory cell or cells affected cannot reliably store data but become stuck at 0 or 1 or switch erratically between 0 and 1 ◼ Can be caused by: ◼ Harsh environmental abuse ◼ Manufacturing defects ◼ Wear ◼ Soft Error ◼ Random, non-destructive event that alters the contents of one or more memory cells ◼ No permanent damage to memory ◼ Can be caused by: ◼ Power supply problems ◼ Alpha particles  SDRAM Advanced DRAM Organization ◼ One of the most critical system bottlenecks when DDR-DRAM using high-performance processors is the interface to main internal memory ◼ The traditional DRAM chip is constrained both by its internal architecture and by its interface to the processor’s memory bus RDRAM ◼ A number of enhancements to the basic DRAM architecture have been explored + ◼ The schemes that currently dominate the market are SDRAM and DDR-DRAM Synchronous DRAM (SDRAM) One of the most widely used forms of DRAM Exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states With synchronous access the DRAM moves data in and out under control of the system clock The processor or other master issues the instruction and address information which is latched by the DRAM The DRAM then responds after a set number of clock cycles Meanwhile the master can safely do other tasks while the SDRAM is processing A0 to A12 Address inputs BA0, BA1 Bank address lines CLK Clock input Table 5.3 CKE Clock enable Chip select SDRAM CS Pin RAS Row address strobe Assignment CAS Column address strobe s WE Write enable DQ0 to DQ15 Data input/output DQM Data mask + Double Data Rate SDRAM (DDR SDRAM) ◼ Developed by the JEDEC Solid State Technology Association (Electronic Industries Alliance’s semiconductor-engineering- standardization body) ◼ Numerous companies make DDR chips, which are widely used in desktop computers and servers ◼ DDR achieves higher data rates in three ways: ◼ First, the data transfer is synchronized to both the rising and falling edge of the clock, rather than just the rising edge ◼ Second, DDR uses higher clock rate on the bus to increase the transfer rate ◼ Third, a buffering scheme is used  DDR1 DDR2 DDR3 DDR4 Prefetch buffer 2 4 8 8 (bits) Voltage level (V) 2.5 1.8 1.5 1.2 Front side bus 200—400 400—1066 800—2133 2133—4266 data rates (Mbps) Table 5.4 DDR Characteristics + Flash Memory ◼ Used both for internal memory and external memory applications ◼ First introduced in the mid-1980’s ◼ Is intermediate between EPROM and EEPROM in both cost and functionality ◼ Uses an electrical erasing technology like EEPROM ◼ It is possible to erase just blocks of memory rather than an entire chip ◼ Gets its name because the microchip is organized so that a section of memory cells are erased in a single action ◼ Does not provide byte-level erasure ◼ Uses only one transistor per bit so it achieves the high density of EPROM Increasing performance and endurance SRAM STT-RAM DRAM PCRAM NAND FLASH ReRAM HARD DISK Decreasing cost per bit, increasing capacity or density Figure 5.18 Nonvolatile RAM within the Memory Hierarchy + Summary Internal Memory Chapter 5 ◼ Semiconductor main memory ◼ DDR DRAM ◼ Organization ◼ Synchronous DRAM ◼ DRAM and SRAM ◼ DDR SDRAM ◼ Types of ROM ◼ Chip logic ◼ Flash memory ◼ Chip packaging ◼ Operation ◼ Module organization ◼ NOR and NAND flash memory ◼ Interleaved memory ◼ Newer nonvolatile solid-state ◼ Error correction memory technologies © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. + Chapter 6 External Memory + Magnetic Disk ◼ A disk is a circular platter constructed of nonmagnetic material, called the substrate, coated with a magnetizable material ◼ Traditionally the substrate has been an aluminium or aluminium alloy material ◼ Recently glass substrates have been introduced ◼ Benefits of the glass substrate: ◼ Improvement in the uniformity of the magnetic film surface to increase disk reliability ◼ A significant reduction in overall surface defects to help reduce read-write errors ◼ Ability to support lower fly heights ◼ Better stiffness to reduce disk dynamics ◼ Greater ability to withstand shock and damage Data are recorded on and later retrieved from the disk via a conducting coil named the head The write mechanism exploits In many systems there are two heads, a the fact that electricity flowing read head and a write head through a coil produces a During a read or write operation the head magnetic field is stationary while the platter rotates beneath it Magnetic Read The write head itself is made of Electric pulses are sent to the write head and the resulting easily magnetizable material and Write and is in the shape of a magnetic patterns are recorded on the surface below, with rectangular doughnut with a gap Mechanisms along one side and a few turns different patterns for positive of conducting wire along the and negative currents opposite side An electric current in the wire Reversing the direction of the induces a magnetic field across current reverses the direction of the gap, which in turn the magnetization on the magnetizes a small area of the recording medium recording medium  Rotation Inter-track gap Track Inter-sector gap S6 S6 Track sector Sector SN S6 S5 SN S5 SN S5 S4 S1 S4 S1 S3 S2 S4 S1 S3 S2 S3 S2 Read-write head (1 per surface) Platter Direction of Cylinder Spindle Boom arm motion Figure 6.2 Disk Data Layout Head Motion Platters Fixed head (one per track) Single platter Movable head (one per surface) Multiple platter Disk Portability Head Mechanism Nonremovable disk Contact (floppy) Removable disk Fixed gap Aerodynamic gap (Winchester) Sides Single sided Double sided Table 6.1 Physical Characteristics of Disk Systems + Characteristics ◼ Fixed-head disk ◼ Removable disk ◼ One read-write head per ◼ Can be removed and track replaced with another disk ◼ Heads are mounted on a ◼ Advantages: fixed ridged arm that ◼ Unlimited amounts of data are extends across all tracks available with a limited number of disk systems ◼ Movable-head disk ◼ A disk may be moved from one computer system to ◼ One read-write head another ◼ Head is mounted on an arm ◼ Floppy disks and ZIP ◼ The arm can be extended cartridge disks are or retracted examples of removable disks ◼ Non-removable disk ◼ Permanently mounted in the ◼ Double sided disk disk drive ◼ Magnetizable ◼ The hard disk in a personal coating is applied computer is a non-removable disk to both sides of the platter + Disk The head mechanism provides a classification of disks into three types Classification ◼ The head must generate or sense an electromagnetic field Winchester Heads of sufficient magnitude to write and read properly ◼ Used in sealed drive assemblies that are almost free of contaminants ◼ The narrower the head, the closer it must be to the platter ◼ Designed to operate closer to the surface to function disk’s surface than conventional rigid ◼ A narrower head means disk heads, thus allowing greater data density narrower tracks and therefore greater data ◼ Is actually an aerodynamic foil that density rests lightly on the platter’s surface when the disk is motionless ◼ The closer the head is to the ◼ The air pressure generated by a disk the greater the risk of spinning disk is enough to make error from impurities or the foil rise above the surface imperfections  Table 6.2 Typical Hard Disk Drive Parameters Characteristics Seagate Seagate Seagate Seagate Laptop Enterprise Barracuda XT Cheetah NS HDD Application Enterprise Desktop Network Laptop attached storage, application servers Capacity 6 TB 3 TB 600 GB 2 TB Average seek 4.16 ms N/A 3.9 ms read 13 ms time 4.2 ms write Spindle speed 7200 rpm 7200 rpm 10, 075 rpm 5400 rpm Average latency 4.16 ms 4.16 ms 2.98 5.6 ms Maximum 216 MB/s 149 MB/s 97 MB/s 300 MB/s sustained transfer rate Bytes per sector 512/4096 512 512 4096 Tracks per 8 10 8 4 cylinder (number of platter surfaces) Cache 128 MB 64 MB 16 MB 8 MB Wait for Wait for Seek Rotational Data Device Channel Delay Transfer Device Busy Figure 6.5 Timing of a Disk I/O Transfer + Disk Performance Parameters ◼ When the disk drive is operating the disk is rotating at constant speed ◼ To read or write the head must be positioned at the desired track and at the beginning of the desired sector on the track ◼ Track selection involves moving the head in a movable-head system or electronically selecting one head on a fixed-head system ◼ Once the track is selected, the disk controller waits until the appropriate sector rotates to line up with the head ◼ Seek time ◼ On a movable–head system, the time it takes to position the head at the track ◼ Rotational delay (rotational latency) ◼ The time it takes for the beginning of the sector to reach the head ◼ Access time ◼ The sum of the seek time and the rotational delay ◼ The time it takes to get into position to read or write ◼ Transfer time ◼ Once the head is in position, the read or write operation is then performed as the sector moves under the head ◼ This is the data transfer portion of the operation + ◼ Consists of 7 levels ◼ Levels do not imply a hierarchical relationship but designate different RAID design architectures that share three common characteristics: 1) Set of physical disk drives viewed by the operating system as a single logical drive 2) Data are distributed across the Redundant Array of physical drives of an array in a scheme known as striping Independent Disks 3) Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure + RAID ◼ Addresses the issues of request patterns of the host system and layout of the data R d a Level 0 ◼ Impact of redundancy does not interfere with analysis i 0 RAID 0 for High Data Transfer Capacity RAID 0 for High I/O Request Rate ◼ For applications to experience a high transfer rate two ◼ For an individual I/O request for a requirements must be met: small amount of data the I/O time 1. A high transfer capacity must is dominated by the seek time and exist along the entire path rotational latency between host memory and the individual disk drives ◼ A disk array can provide high I/O execution rates by balancing the 2. The application must make I/O I/O load across multiple disks requests that drive the disk array efficiently ◼ If the strip size is relatively large multiple waiting I/O requests can be handled in parallel, reducing the queuing time for each request + R RAID a Level 1 i d Characteristics Positive Aspects ◼ Differs from RAID levels 2 through 6 ◼ A read request can be serviced by in the way in which redundancy is either of the two disks that contains 1 achieved the requested data ◼ Redundancy is achieved by the ◼ There is no “write penalty” simple expedient of duplicating all the data ◼ Recovery from a failure is simple, when a drive fails the data can be ◼ Data striping is used but each logical accessed from the second drive strip is mapped to two separate physical disks so that every disk in ◼ Provides real-time copy of all data the array has a mirror disk that contains the same data ◼ Can achieve high I/O request rates if the bulk of the requests are reads ◼ RAID 1 can also be implemented without data striping, although this is ◼ Principal disadvantage is the cost less common + R 2 RAID a Level 2 i d Characteristics Performance ◼ An error-correcting code is ◼ Makes use of a parallel access calculated across corresponding technique bits on each data disk and the bits of the code are stored in the corresponding bit positions on ◼ In a parallel access array all multiple parity disks member disks participate in the execution of every I/O request ◼ Typically a Hamming code is used, which is able to correct single-bit ◼ Spindles of the individual drives errors and detect double-bit are synchronized so that each errors disk head is in the same position on each disk at any given time ◼ The number of redundant disks is proportional to the log of the number of data disks ◼ Data striping is used ◼ Strips are very small, often as ◼ Would only be an effective choice small as a single byte or word in an environment in which many disk errors occur + R RAID a Level 3 i d Redundancy Performance ◼ Requires only a single ◼ In the event of a drive failure, the redundant disk, no matter how parity drive is accessed and data is reconstructed from the remaining 3 large the disk array devices ◼ Employs parallel access, with ◼ Once the failed drive is replaced, the data distributed in small strips missing data can be restored on the new drive and operation resumed ◼ Instead of an error correcting ◼ In the event of a disk failure, all of the code, a simple parity bit is data are still available in what is computed for the set of referred to as reduced mode individual bits in the same position on all of the data disks ◼ Return to full operation requires that the failed disk be replaced and the entire contents of the failed disk be ◼ Can achieve very high data regenerated on the new disk transfer rates ◼ In a transaction-oriented environment performance suffers + RAID R a Level 4 i d Characteristics Performance ◼ Makes use of an independent access technique ◼ Involves a write penalty when 4 ◼ In an independent access array, an I/O write request of small each member disk operates size is performed independently so that separate I/O requests can be satisfied in parallel ◼ Each time a write occurs the array management software ◼ Data striping is used must update not only the user ◼ Strips are relatively large data but also the corresponding parity bits ◼ To calculate the new parity the array management software ◼ Thus each strip write involves must read the old user strip two reads and two writes and the old parity strip + RAID RAID R a Level 5 Level 6 i d Characteristics Characteristics ◼ Organized in a similar fashion ◼ Two different parity calculations 5 to RAID 4 are carried out and stored in 6 separate blocks on different disks ◼ Difference is distribution of the parity strips across all ◼ Advantage is that it provides disks extremely high data availability ◼ A typical allocation is a round- ◼ Three disks would have to fail robin scheme within the mean time to repair (MTTR) interval to cause data to be lost ◼ The distribution of parity strips across all drives avoids ◼ Incurs a substantial write the potential I/O bottleneck penalty because each write found in RAID 4 affects two parity blocks  Table 6.4 RAID Comparison (page 1 of 2)  Table 6.4 RAID Comparison (page 2 of 2) + SSD Compared to HDD ◼ SSDs have the following advantages over HDDs: ◼ High-performance input/output operations per second (IOPS) ◼ Durability ◼ Longer lifespan ◼ Lower power consumption ◼ Quieter and cooler running capabilities ◼ Lower access times and latency rates  NAND Flash Drives Seagate Laptop Internal HDD File copy/write speed 200—550 Mbps 50—120 Mbps Power draw/battery life Less power draw, averages 2– More power draw, averages 3 watts, resulting in 30+ 6–7 watts and therefore uses minute battery boost more battery Storage capacity Typically not larger than 512 Typically around 500 GB and GB for notebook size drives; 1 2 TB maximum for notebook TB max for desktops size drives; 4 TB max for desktops Cost Approx. $0.50 per GB for a 1- Approx $0.15 per GB for a 4- TB drive TB drive Table 6.5 Comparison of Solid State Drives and Disk Drives  Host System Operating System Software File System Software I/O Driver Software Interface Interface SSD Controller Addressing Data buffer/ Error cache correction Flash memory components Flash memory components Flash memory components Flash memory components Figure 6.8 Solid State Drive Architecture + Practical Issues There are two practical issues peculiar to SSDs that are not faced by HDDs: ◼ Flash memory becomes ◼ SDD performance has a unusable after a certain tendency to slow down as the number of writes device is used ◼ Techniques for prolonging life: ◼ The entire block must be ◼ Front-ending the flash with a read from the flash memory cache to delay and group and placed in a RAM buffer write operations ◼ Using wear-leveling ◼ Before the block can be algorithms that evenly written back to flash distribute writes across block memory, the entire block of of cells flash memory must be ◼ Bad-block management techniques erased ◼ Most flash devices estimate ◼ The entire block from the their own remaining lifetimes buffer is now written back to so systems can anticipate the flash memory failure and take preemptive action CD Compact Disk. A nonerasable disk that stores digitized audio information. The standard system uses 12-cm disks and can record more than 60 minutes of uninterrupted playing time. CD-ROM Compact Disk Read-Only Memory. A nonerasable disk used for storing computer data. The standard system uses 12-cm disks and can hold more than 650 Mbytes. CD-R CD Recordable. Similar to a CD-ROM. The user can write to the disk only once. Table 6. 6 CD-RW CD Rewritable. Similar to a CD-ROM. The user can erase and rewrite to the disk multiple times. Optical DVD Digital Versatile Disk. A technology for producing digitized, compressed representation Disk of video information, as well as large volumes of other digital data. Both 8 and 12 cm diameters are used, with a double-sided capacity of up to 17 Gbytes. The basic DVD is read-only (DVD- Products ROM). DVD-R DVD Recordable. Similar to a DVD-ROM. The user can write to the disk only once. Only one-sided disks can be used. DVD-RW DVD Rewritable. Similar to a DVD-ROM. The user can erase and rewrite to the disk multiple times. Only one-sided disks can be used. Blu-Ray DVD High definition video disk. Provides considerably greater data storage density than DVD, using a 405-nm (blue-violet) laser. A single layer on a single side can store 25 Gbytes. + Compact Disk Read-Only Memory (CD-ROM) ◼ Audio CD and the CD-ROM share a similar technology ◼ The main difference is that CD-ROM players are more rugged and have error correction devices to ensure that data are properly transferred ◼ Production: ◼ The disk is formed from a resin such as polycarbonate ◼ Digitally recorded information is imprinted as a series of microscopic pits on the surface of the polycarbonate ◼ This is done with a finely focused, high intensity laser to create a master disk ◼ The master is used, in turn, to make a die to stamp out copies onto polycarbonate ◼ The pitted surface is then coated with a highly reflective surface, usually aluminum or gold ◼ This shiny surface is protected against dust and scratches by a top coat of clear acrylic ◼ Finally a label can be silkscreened onto the acrylic + ◼ CD-ROM is appropriate for the distribution of large CD-ROM amounts of data to a large number of users ◼ Because the expense of the initial writing process it is not appropriate for individualized applications ◼ The CD-ROM has two advantages: ◼ The optical disk together with the information stored on it can be mass replicated inexpensively ◼ The optical disk is removable, allowing the disk itself to be used for archival storage ◼ The CD-ROM disadvantages: ◼ It is read-only and cannot be updated ◼ It has an access time much longer than that of a magnetic disk drive + CD Recordable CD Rewritable (CD-R) (CD-RW) ◼ Write-once read-many ◼ Can be repeatedly written and overwritten ◼ Accommodates applications in ◼ Phase change disk uses a material that which only one or a small has two significantly different number of copies of a set of data reflectivities in two different phase states is needed ◼ Amorphous state ◼ Disk is prepared in such a way ◼ Molecules exhibit a random that it can be subsequently orientation that reflects light poorly written once with a laser beam ◼ Crystalline state of modest-intensity ◼ Has a smooth surface that reflects light well ◼ Medium includes a dye layer which is used to change ◼ A beam of laser light can change the reflectivity and is activated by a material from one phase to the other high-intensity laser ◼ Disadvantage is that the material eventually and permanently loses its ◼ Provides a permanent record of desirable properties large volumes of user data ◼ Advantage is that it can be rewritten Protective acrylic Label Land Pit Polycarbonate Aluminum plastic Laser transmit/ receive Figure 6.9 CD Operation CD 2.11 µm Data layer Beam spot Land Pit 1.2 µm 0.58 µm Blu-ray Track laser wavelength = 780 nm 0.1 µm 1.32 µm DVD 405 nm 0.6 µm 650 nm Figure 6.12 Optical Memory Characteristics + Magnetic Tape ◼ Tape systems use the same reading and recording techniques as disk systems ◼ Medium is flexible polyester tape coated with magnetizable material ◼ Coating may consist of particles of pure metal in special binders or vapor-plated metal films ◼ Data on the tape are structured as a number of parallel tracks running lengthwise ◼ Serial recording ◼ Data are laid out as a sequence of bits along each track ◼ Data are read and written in contiguous blocks called physical records ◼ Blocks on the tape are separated by gaps referred to as inter-record gaps Track 2 Track 1 Track 0 Direction of Bottom read/write edge of tape (a) Serpentine reading and writing Track 3 4 8 12 16 20 Track 2 3 7 11 15 19 Track 1 2 6 10 14 18 Track 0 1 5 9 13 17 Direction of tape motion (b) Block layout for system that reads/writes four tracks simultaneously Figure 6.13 Typical Magnetic Tape Features  Table 6.7 LTO Tape Drives LTO-1 LTO-2 LTO-3 LTO-4 LTO-5 LTO-6 LTO-7 LTO-8 Release date 2000 2003 2005 2007 2010 TBA TBA TBA Compressed 200 GB 400 GB 800 GB 1600 GB 3.2 TB 8 TB 16 TB 32 TB capacity Compressed 40 MB/s 80 MB/s 160 MB/s 240 MB/s 280 MB/s 525 MB/s 788 MB/s 1.18 GB/s transfer rate (MB/s) Linear density 4880 7398 9638 13250 15142 (bits/mm) Tape tracks 384 512 704 896 1280 Tape length 609 m 609 m 680 m 820 m 846 m Tape width (cm) 1.27 1.27 1.27 1.27 1.27 Write elements 8 8 16 16 16 WORM? No No Yes Yes Yes Yes Yes Yes Encryption No No No Yes Yes Yes Yes Yes Capable? Partitioning? No No No No Yes Yes Yes Yes + Summary External Memory Chapter 6 ◼ RAID ◼ Magnetic disk ◼ RAID level 0 ◼ Magnetic read and write mechanisms ◼ RAID level 1 ◼ Data organization and ◼ RAID level 2 formatting ◼ RAID level 3 ◼ Physical characteristics ◼ RAID level 4 ◼ Disk performance parameters ◼ RAID level 5 ◼ RAID level 6 ◼ Solid state drives ◼ SSD compared to HDD ◼ Optical memory ◼ SSD organization ◼ Compact disk ◼ Practical issues ◼ Digital versatile disk ◼ Magnetic tape ◼ High-definition optical disks