Seagate Cheetah 15K.5, full of perpendicular goodness with 300 GB space and a mad 15,000 rpm

Seagate Cheetah 15K.5, full of perpendicular goodness with 300 GB space and a mad

15,000 rpm

2Systems Architecture, Fifth Edition

Chapter Goals

• Describe the distinguishing characteristics of primary and secondary storage

• Describe the devices used to implement primary storage

• Describe memory allocation schemes• Compare and contrast secondary storage

technology alternatives

Chapter Goals (continued)

• Describe factors that determine storage device performance

• Choose appropriate secondary storage technologies and devices

Storage Devices

• Consist of a read/write mechanism and a storage medium– Device controller provides interface

• Primary storage devices– Support immediate execution of programs

• Secondary storage devices– Provide long-term storage of programs and data

Characteristics of Storage Devices

• Speed• Volatility• Access method• Portability• Cost and capacity

• Primary storage speed– Typically faster than secondary storage speed by a

factor of 105 or more

– Expressed in nanoseconds (billionths of a second)

• Secondary storage speed– Expressed in milliseconds (thousandths of a second)

• Data transfer rate = 1 second/access time (in seconds) x unit of data transfer (in bytes)

Volatility

• Primary storage devices are generally volatile– Cannot reliably hold data for long periods

• Secondary storage devices are generally nonvolatile– Hold data without loss over long periods of time

Access Method

• Serial access (linear)• Random access (direct access)• Parallel access (simultaneous)

Portability

• Removable storage media with standardized formats (e.g., compact disc and tape storage)

• Typically results in slower access speeds

Cost and Capacity

• Cost increases:– With improved speed, volatility, or portability

– As access method moves from serial to random to parallel access method

• Primary storage - expensive (high speed and combination of parallel/random access methods)

• Capacity of secondary storage devices is greater than primary storage devices

Memory-Storage Hierarchy

Primary Storage Devices

• Critical performance characteristics– Access speed

– Data transfer unit size

• Must closely match CPU speed and word size to avoid wait states

Storing Electrical Signals

• Directly– By devices such as batteries and capacitors

– Trade off between access speed and volatility

• Indirectly– Uses energy to alter the state of a device; inverse

process regenerates equivalent electrical signal

• Modern computers use memory implemented with semiconductors (RAM and NVM)

Random Access Memory

• Characteristics– Microchip implementation using semiconductors

– Ability to read and write with equal speed

– Random access to stored bytes, words, or larger data units

• Basic types– Static RAM (SRAM) – uses transistors

– Dynamic RAM (DRAM) – uses transistors and capacitors

Random Access Memory

• To bridge performance gap between memory and microprocessors– Read-ahead memory access

– Synchronous read operations

– On-chip memory caches

Nonvolatile Memory

• Random access memory with long-term or permanent data retention

• Usually relegated to specialized roles and secondary storage; slower write speeds and limited number of rewrites

• Generations of devices (ROM, Erasable Programmable ROM=EPROM, and Electronically EPROM = EEPROM)

Nonvolatile Memory

• Flash RAM (most common NVM)– Competitive with DRAM in capacity and read

performance

– Relatively slow write speed

– Limited number of write cycles

• NVM technologies under development– Ferroelectric RAM

– Polymer memory

Memory Packaging

• Dual in-line packages (DIPs)– Early RAM and ROM circuits

• Single in-line memory module (SIMM)– Standard RAM package in late 1980s

• Double in-line memory module (DIMM)– Newer packaging standard

– A SIMM with independent electrical contacts on both sides of the module

CPU Memory Access

• Critical design issues for primary storage devices and processors– Physical organization of memory

– Organization of programs and data within memory

– Method(s) of referencing specific memory locations

Physical Memory Organization

• Physical memory– Actual number of memory bytes that physically are

installed in the machine

• Most and least significant bytes• Big endian and little endian• Addressable memory

– Highest numbered storage byte that can be represented

Memory Allocation and Addressing

• Memory allocation– Assignment of specific memory addresses to

system software, application programs, and data

• Absolute addressing• Indirect addressing (relative addressing)

– Offset register

Magnetic Storage

• Exploits duality of magnetism and electricity– Converts electrical signals into magnetic charges

– Captures magnetic charge on a storage medium

– Later regenerates electrical current from stored magnetic charge

• Polarity of magnetic charge represents bit values zero and one

Magnetic Tape

• Ribbon of plastic with a coercible (usually metallic oxide) surface coating

• Mounts in a tape drive for reading and writing• Relatively slow serial access• Compounds magnetic leakage; wraps upon itself• Susceptible to stretching, friction, temperature

variations

Magnetic Tape

• Two approaches to recording data– Linear recording

– Helical scanning

• Several formats and standards (e.g., DDS [DAT], AIT, Mammoth, DLT, LTO)

Magnetic Disk

• Flat, circular platter with metallic coating that is rotated beneath read/write heads

• Random access device; read/write head can be moved to any location on the platter

• Hard disks and floppy disks• Cost performance leader for general-purpose

on-line secondary storage

Locating a Block of Data• Average seek time: (average) time required

to move from one track to another• [Also called track-to-track seek time]

• Latency: time required for disk to rotate to beginning of correct sector

• [Also called rotational delay]

• Transfer time: time required to transfer a block of data to the disk controller buffer

Disk Access Times

• Avg. Seek time (track-to-track seek time)– average time to move from one track to another

• Avg. Latency time (rotational delay– average time to rotate to the beginning of the sector

– Avg. Latency time = ½ * 1/rotational speed

• Transfer time– 1/(# of sectors * rotational speed)

• Total Time to access a disk block– Avg. seek time + avg. latency time + avg. transfer time

Example• Calculate the average access time for a disk rotating at

7,200 rpm, with Avg. Seek time 5 microseconds, and 500 sectors/track.

• SOL: Average Access Time =(seek) + (rot. Delay) + (Transfer Time)

• Average Access Time =(5 microseconds) + (½) * (1/7,200RPM) + 1/(500* 7,200RPM

• =.000005 + ½ * .0001389 (60 sec) + .000000278 (60 sec)

• =.000005+.004167+.0000167=.0041887sec….ANS

• Which performance value is the most significant?

Disk Block FormatsSingle Data Block

Header for Windows disk

To increase capacity per platter, disk manufacturers divide tracks into zones and vary the sectors per track in each zone.

Optical Mass Storage Devices

• Store bit values as variations in light reflection• Higher areal density and longer data life than

magnetic storage• Standardized and relatively inexpensive• Uses: read-only storage with low performance

requirements, applications with high capacity requirements, and where portability in a standardized format is needed

Optical storage devices read data by shining laser beam on the disc.

Layout: CD-ROM vs. Standard Disk

CD-ROM Hard Disk

CD-ROM

• Read-only; data permanently embedded in durable polycarbonate disc

• Bit values represented as flat areas (lands) and concave dents (pits) in the reflective layer

• Data recorded in single continuous track that spirals outward from center of disc

• Popular medium for distributing software and large data sets

CD-ROM

Advantages Drawbacks

• Standardized format• High density• Cheap to manufacture

• Cannot be rewritten• Capacity limited to 700

• Uses a laser that can be switched between high and low power and a laser-sensitive dye embedded in the disc

• Relatively cheap• Common uses: create music CDs on home

computers, back up data from other storage devices, create archives of large data sets, and manufacture small quantities of identical CDs

Phase-Change Optical Discs

• Enables nondestructive writing to optical storage media

• Materials change state easily from non-crystalline (amorphous), to crystalline, and then back again– Reflective layer is a compound of tellurium,

selenium, and tin

• Example: CD-RW

• Improves on CD and CD-RW technology– Increased track and bit density: smaller wavelength

lasers and more precise mechanical control

– Improved error correction

– Multiple recording sites and layers

Summary

• Storage devices and their underlying technologies

• Characteristics common to all storage devices

• Technology, strengths, and weaknesses of primary and secondary storage

Solid State Drive!• In 1984, Dr. Fujio Masuoka from Toshiba

invented the first flash memory, which Intel introduced as a commercial product four years later. Solid state drives based on flash memory have a number of unique advantages over conventional hard drive technology. Since they lack mechanical parts, they are much more resistant to shock, consume far less power, and release far less heat. They also produce no sound during operation and respond much more quickly than a mechanical drive. The size of a flash drive can also be very small (relative to a mechanical hard drive), resulting in a lighter device. All these advantages beg the question 'Why are we still using what might seem as an outdated mechanical hard drive technology?'

Fastest Memory (Aug 2008)

The fastest memory on the market was showcased by Corsair. The company displayed the DDR3-2133MHz memory modules, which have a 1GB capacity and are capable of performing at latencies of 8-8-8-24. These “Dominator” modules are integrated with the company’s unique Dual-path Heat eXchange (DHX) technology. The DHX utilizes two paths for heat removal – an aluminum heat spreader, and a special PCB, which has a copper base that absorbs heat transferred by a dedicated heat sink. According to the company, the DHX modules, each of which includes a total of four heat sinks, provide an extremely stable, reliable, and overclockable memory.

• http://thefutureofthings.com/news/1143/a-look-back-at-cebit-2008-storage-and-memory.html

PCI Drive??

• The DDR Drive X1 is a PCI Express based plug in card with 8GB of capacity, and bootable.

• According to sources close to the firm, the drive will have a custom and upgradeable high performance DMA Engine, an external power jack with a switching AC adaptor, and will go into a 512 unit initial production run.

• Although the firm gave no details of the pricing, a solid state drive at an affordable price is likely to be a popular item.

• http://www.theinquirer.net/en/inquirer/news/2006/01/03/solid-state-ddr-drive-goes-into-prototype

Seagate Cheetah 15K.5, full of perpendicular goodness with 300 GB space and a mad 15,000 rpm

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