Secondary Memory Devices Information is moved Secondary memory between main memory Central devices provide and secondary memory long-term storage Processing as needed Unit Hard disks Floppy disks ZIP disks Writable CDs Writable DVDs Tapes © 2004 Pearson Addison-Wesley. All rights reserved Hard Disk Main Memory Floppy Disk 1-7
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Secondary Memory Devices Secondary memory devices provide long-term storage Hard disks Floppy disks ZIP disks Writable CDs Tapes Central Processing Unit Information is moved between main memory and secondary memory as needed Hard Disk Main Memory Floppy Disk 3
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References: 1. Fabrication Procedures and Process Sensitivities for CdS/CdTe Solar Cells 2. Growth and physical properties of CdS thin films prepared by chemical bath deposition 3. Influence of CdS window layer on 2-mm thick CdS/CdTe thin film solar cells 4. Photoluminescence characteristics of CdS layers deposited in a chemical bath 5. High throughput processing of CdTe/CdS solar cells 6. Influence of ITO surface modification on the growth of CdS 7. Growth of polycrystalline CdS and CdTe thin layers for high efficiency thin film solar cells 8. CdS films prepared by the close-spaced sublimation 9. Effects of thiourea concentration on CdS thin films grown by chemical bath deposition 10.The Effect of Oxygen on Interface Microstructure Evolution in CdS/CdTe Solar Cells 11. Recent progress on CdTe/CdS thin film solar cells 12. Nano-structured CdTe, CdS and TiO2 for thin film solar cell applications 13. Ordered CdTe/CdS Arrays for High-Performance Solar Cells
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3, CdS improvement method 3.1, H2 treatment of CdS CdS by CBD can make a very compact film, but CBD is not suitable for largescale production since it is not fast and gives a waste. CdS by sputtering was grown in presence of fluorine by introducing in the sputtering chamber Ar containing 3% of CHF3. Despite fluorine is a donor for CdS, we did not see any lowering of the CdS resistivity when it was grown in presence of fluorine. The CSS(500 ℃, sticking of CdS by gas pressure and close to source ) allows substrate deposition temperature much higher than that of vacuum evaporation(<150 ℃, if >150 ℃ S will re-evaporated before combining with Cd ). Both CdS(F) by sputtering or CdS(O) by CSS are suitable to make high efficiency cells if they are treated for 20 min, in Ar containing 20% of H 2 at 400 ℃ substrate temperature because CdS(F) contains CdF2 segregated in the grain boundaries and surface. CdF2 is useful to passivate the grain boundaries, but it block CdS to interact with CdTe. The same happens for CdS, because CdO and/or CdSO3 formed in the grain boundaries and surface. They can be removed by the H2 treatment. The thickness of the CdS layer is, in both cases, 80 nm.
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Computer Organization (Secondary storage) ◦ Secondary storage unit. This is the long-term, high-capacity “warehousing” section. Programs or data not actively being used by the other units normally are placed on secondary storage devices (ex., hard drive) until they’re needed again, possibly hours, days, months or even years later. ◦ Therefore, information on secondary storage devices is said to be persistent - it is preserved even when the computer’s power is turned off. Secondary storage information takes much longer to access than information in primary memory, but the cost per unit of secondary storage is much less than that of primary memory.  Examples of secondary storage devices include CDs, DVDs and USB drives, which can hold hundreds of millions to billions of characters. 22
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Introduction to the new mainframe Physical storage used by z/OS Conceptually, mainframes and all other computers have two types of physical storage: • Physical storage located on the mainframe processor itself. - This is memory, often called processor storage, real storage, central storage (CSTOR) or MAIN storage. • Physical storage external to the mainframe, including storage on direct access devices, such as disk drives, and tape drives. - For z/OS usage, this storage is called page storage or auxiliary storage. One difference between the two kinds of storage relates to the way in which they are accessed, as follows: • Central storage is accessed synchronously with the processor, that is, the processor must wait while data is retrieved from central storage. • Auxiliary storage is accessed asynchronously. The processor accesses auxiliary storage through an input/output (I/O) request, which is scheduled to run amid other work requests in the system. - During an I/O request, the processor is free to execute other, unrelated work. Many computers also have a fast memory, local to the processor, called the processor cache. The cache is not visible to the programmer or application programs or even the operating system directly. © Copyright IBM Corp., 2010. All rights reserved. Page 17 of 85
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Redundant Array of Independent Disks (RAID) Data organization on multiple disks Data disk 0 Data disk 1 Data disk 2 Mirror disk 0 Mirror disk 1 RAID0: Multiple disks for higher data rate; no redundancy Mirror disk 2 RAID1: Mirrored disks RAID2: Error-correcting code DataA disk 0 DataB disk 1 DataC disk 2 Data D disk 3 Parity P disk Spare disk RAID3: Bit- or b yte-level striping with parity/checksum disk ABCDP=0 B=ACDP Data 0 Data 1 Data 2 Data 0’ Data 1’ Data 2’ Data 0” Data 1” Data 2” Data 0’” Data 1’” Data 2’” Parity 0 Parity 1 Parity 2 Spare disk RAID4: Parity/checksum applied to sectors,not bits or bytes Data 0 Data 1 Data 2 Data 0’ Data 1’ Data 2’ Data 0” Data 1” Parity 2 Data 0’” Parity 1 Data 2” Parity 0 Data 1’” Data 2’” Spare disk RAID5: Parity/checksum distributed across several disks RAID6: Parity and 2nd check distributed across several disks Fig. 19.5 RAID levels 0-6, with a simplified view of data organization. Computer Architecture, Memory System Design Slide 50
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Sample Student Schedule Grade 9 English Social Studies Math Science Foreign Language Intro to Engineering Design Physical Education Grade 10 1 unit 1 unit 1 unit 1 unit 1 unit 1 unit .5 unit Grade 11 1 unit 1 unit 1 unit 1 unit 1 unit 1 unit .5 unit Grade 12 English Social Studies Math Science Digital Electronics 1 unit 1 unit 1 unit 1 unit *Computer Integrated Manufacturing 1 unit *Civil Engineer and Architecture *Biotechnical Engineering *Aerospace Engineering Physical Education English Social Studies Math Science Foreign Language Principles of Engineering Physical Education 1 unit .5 unit English Social Studies Math Science Engineering Design and Development Health Physical Education 1 unit 1 unit 1 unit 1 unit 1 unit .5 unit .5 unit
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Identifying Your System Configuration Different system configurations:  One hard disk drive, one CD-ROM drive, and one floppy disk drive  One hard disk drive, one CD-ROM drive, one floppy disk drive, and one Zip drive  Two hard disk drives, one CD-ROM drive, and one floppy disk drive  One hard disk drive, one CD-ROM drive, one readwrite CD-ROM drive, and one floppy disk drive Ch1 26
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Introduction to the new mainframe z/OS operating environment • An address space describes the virtual storage addressing range available to a user or program. • Two types of physical storage are available: main storage and auxiliary storage (AUX). - Main storage is also referred to as real storage or real memory. - The Real Storage Manager (RSM) controls the allocation of central storage during system initialization, and pages in user or system functions during execution. - The auxiliary storage manager controls the use of page and swap data sets. z/OS moves programs and data between central storage and auxiliary storage through processes called paging and swapping. • z/OS dispatches work for execution (not shown in previous the figure), that is, it selects programs to be run based on priority and the ability to execute and then loads the program and data into central storage. - All program instructions and data must be in central storage when executing. • An extensive set of facilities manages files stored on direct access storage devices (DASDs) or tape cartridges. • Operators use consoles to start and stop z/OS, enter commands, and manage the operating system. © Copyright IBM Corp., 2010. All rights reserved. Page 19 of 85
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Storage Devices 7 Memory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. There are three main types of storage devices:Disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives. Bus Storage Devices e.g., Disk, CD, and Tape Memory CPU Communication Devices Input Devices Output Devices e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer
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Storage Devices Memory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. There are three main types of storage devices:Disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives. Bus Storage Devices e.g., Disk, CD, and Tape Memory CPU Communication Devices Input Devices Output Devices e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 6
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Storage and Memory • They refer to storage areas in the computer. The term memory identifies data storage that usually comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. However, the difference is blurring as solid state (SD) disk storages are in the form of chips. • Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. • Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. • Today’s computers also come with hard disk drives that are used to store permanent data. • The content in memory is usually lost when the computer is powered down, unless it’s flash memory (as in your thumb drives or SD cards) but data on hard drives are not. • The earliest PCs did not have hard drives – they store data on and boot from floppy disks.
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Tertiary (Removable) Storage • Characteristic: Low cost, high capacity • Examples – Removable magnetic disks: nearly as fast as hard disks, but less reliable – A magneto-optic disk: records on rigid platter coated with magnetic material • The read write heads are further from the head, resistant to head crash • lasers used to amplify magnetic material for write and detect – Optical disks: Altered by laser light. Very durable and reliable. – Tape: Falling price gap between tapes and disks, makes these less popular • Hierarchical Storage Management (HSM) – – – – – Extends primary and secondary storage to include tertiary storage Found in supercomputing centers that have enormous volumes of data Usually implemented as a jukebox of removable disks Disk-resident files are archived to a tape or disk library for low cost storage. Files are automatically staged back (slowly) to disk for active use Note: fixed drives tend to be more reliable than removable ones
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RAID: Level 2 (Redundancy via Hamming ECC) Checks sec1,b0 sec1,b1 sec1,b2 sec1,b3 4,5,6,7 1 0 1 0 1 3 5 6 0 7 error 4 Checks 2,3,6,7 Checks 1,3,5,7 0 1 2 1 ECC disks ECC disks 4 and 2 point to either data disk 6 or 7 as being bad, but ECC disk 1 says disk 7 is okay, so disk 6 must be in error Why it works. 1 001 2 010 21 011 4 100 4 1 101 42 110 421 111 1 2 3 4 5 6 7 ECC: 421 ECC (Hamming Error Correcting Code) disks contain the even-parity of data on a set of distinct overlapping disks  # ECC redundant disks = log2 (total # of data + ECC disks) so almost twice the cost of one big disk if small # of data disks used. - writes require computing parity to write to “half” the ECC disks - reads require reading “half” the ECC disks and confirming parity  Can tolerate limited disk failure, since the data can be reconstructed; first correction method; no longer used. 12/8-10/09 CSE502-F09, Lec 22+23 Disk Storage 22
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Floppy Disks What is a floppy disk drive?  Device that reads from and writes to floppy disk   One floppy drive, named drive A If two floppy drives, second designated as drive B Floppy disk drive built into a desktop computer External floppy disk drive attaches to a computer with a cable p. 212 Fig. 6-3 Next
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2.3.6 Secondary Storage • Secondary storage stores large quantities of persistent data at low cost – Accessing data on a hard disk is slower than main memory • Mechanical movement of read/write head • Rotational latency • Transfer time – Removable secondary storage facilitates data backup and transfer • • • • • • CDs (CD-R, CD-RW) DVDs (DVD-R, DVD+R) Zip disks Floppy disks Flash memory cards Tapes  2004 Deitel & Associates, Inc. All rights reserved.
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