1. Chapter 5 Data Storage Technology
Storage Device Characteristics
Storage Medium
Device or substance that holds the data
Electrical circuits (memory)
Polymers and metal oxides (tapes)
Read/Write Mechanisms
The method of reading/writing data to/from a storage medium
Electro-mechanical (tapes, disks)
Device Controller (communicates with the software driver)
Interface between the system bus and the storage device
Electronic hardware unit

2. Storage Device Characteristics
CPU
I/O Device
Operating System
Device Controller
Read/Write Mechanism
DRIVER
Storage Medium

3. Storage Devices Distinguishing Characteristics
Speed
Volatility
Access method
Portability
Cost and capacity

4. Storage Devices Distinguishing Characteristics
Speed
Most important distinguisher between Primary (memory) and Secondary storage
Extends capacity of CPU register
CPU and execution cycle are short compared to secondary device transfer speed
Secondary storage speed
Effects overall computer performance
Starting program execution
Transfer of data
Access Time: time required to execute one read or write operation completely

5. Speed Total Access Time determined by Access time
Time required to execute one read or write operation completely
Data transfer unit
Vary from one storage device to another
CPU: usually a word
I/O devices:
Blocks: larger than words
Block size
Device dependent
Sector: magnetic and optical

6. Speed Data Transfer Rate Computed 1 Unit of
X data transfer = data transfer rate
Total access time (bytes) (seconds)
Access time = 15 nanoseconds
Unit of data transfer = 4 bytes (32 bits)
/ 1,000,000, = second billion one nanosecond
x = one nanosecond access time total access time
/ = ,666, second total access time # of accesses times nanoseconds per second
4. 66,666, x = 266,666, # # of access times bytes bytes/second per second

7. Speed Milliseconds: thousandths of a second 1/1,000 second = .001
Microseconds: millionths of a second
1/1,000,000 second =
Nanoseconds: billionths of a second
1/1,000,000,000 second =

8. Storage Devices Distinguishing Characteristics
Volatility
Volatile: the device cannot reliably hold data for a long period of time
Primary storage (memory) Video cards
Non-volatile: a device holds data without loss over a long period of time
Hard drives Floppy disks Tapes CDs DVDs
Device may become volatile
Magnetic decay
Obsolescence

9. Storage Devices Distinguishing Characteristics
Access Methods
Serial Access
Random Access
Parallel Access
Stores and retrieves data in a linear, sequential order
Access time is dependent upon where the read/write mechanism and the desired data are located
Not used for frequently required data due to slow access times
i.e.: tape units

10. Storage Devices Distinguishing Characteristics
Access Method
Random Access
Not as restricted to location of read/write mechanism or data
Primary storage (memory): access time is constant as it is electronic and not hampered by physical movements
Disk assess time varies as there is a physical dependency on the location of the read/write mechanism and the data
Parallel Access
Simultaneously accessing multiple storage locations
Primary storage (memory)
Operating systems (some)
Store a single file on different secondary storage (disk) devices at the same time. Segment the file.

11. Storage Devices Distinguishing Characteristics
Access Method
Portability
Removable storage medium
Slower access times
Lack of environmental control
Cost and Capacity
Increased cost
Increase in speed
Permanence (volatility)
Access method
Serial
Random
Parallel

12. Primary Storage Devices
Performance Characteristics
Access time
Data transfer unit size
CPU memory (registers)
Fastest memory access
Less physical memory
More costly memory
Primary storage
Slower access than the CPU memory
Less costly
Greater amount of memory

13. Primary Storage Devices
Random Access Memory (RAM)
Read and Write with equal speed
Random access to stored data
Static RAM (SRAM)
Flip-flop circuits suing two transistors
Remains in one of two states
(0 or 1 state)
Volatile
More expensive
Dynamic RAM (DRAM)
Transistors and capacitors
Capacitors must be continually refreshed
Slower than SRAM due to refresh cycle
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14. Primary Storage Devices
Performance increase
Read ahead memory access
Synchronous DRAM (SDRAM)
Read (anticipate) the next instruction location
Synchronous read operations
Enhanced DRAM (EDRAM) (Cached DRAM)
When data is requested, the words around the requested data are also fetched and stored in the SRAM
On-chip caching
Ferroelectric RAM Iron chips, similar to core, stored on the microchip

15. Primary Storage Devices
Read-Only Memory (ROM)
Random access
Storage of data (firmware)
Permanent semi permanently (volatile)
System boot program and BIOS
Electronically Erasable Programmable Read-only Memory (EEPROM)
Programmed, erased, and reprogrammed Require high voltages
Flash Memory
Erased and re-written more quickly Limited life span Programs and data that are not frequently updated

16. Primary Storage Devices
Memory Packaging
Circuits embedded within microchips
Groups of chips are packed on circuit boards Easily installed and removed
Single In-line Memory Module (SIMM)
Memory chips on single boards Boards have electrical contacts which incorporate into slots on the motherboard
Double In-line Memory Module (DIMM)
Double sided SIMM

17. CPU Memory Access Primary Storage (memory)
Contiguous memory cells (bytes)
Each byte is addressable Starting at address 0 through the end
Numeric values Highest position weight left to right (what we have been doing)
Most significant byte Left most byte High order byte
Least significant byte Right most byte Low order byte
Big endian Stores the most significant byte at the lowest address
Little endian (most common) Stores the least significant byte at the lowest address
Addressable memory Determined by size of address register
Physical memory The actual memory available for use
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18. CPU Memory Access Memory Allocation and Addressing
Memory Allocation The assignment of specific memory addresses
Operating system occupies lowest memory block
Programs begin following OS memory
Program Offset The difference between where a program instruction is located and address zero (0) Offset Register Segment Register Used with Indirect addressing Relative addressing Address = Segment Register + Offset Register
Absolute Addressing Memory address that refers to an actual physical memory location
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19. Magnetic Storage
Write data Electrical signals are converted to magnetic charges
Read data Magnetic charge is converted to an electrical signal
Polarity of the charge determines the data value one (1) or zero (0)
Problems
Magnetic Decay Loss of charge over time
Magnetic Leakage Polarity of the magnetic charges may affect surrounding charges of other bits
Storage Density
Coercivity The ability of a substance to accept and hold a magnetic charge Varies among elements and compounds
Recording density The amount of surface area allocated to a bit
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20. Magnetic Storage
Media Integrity Depends upon construction and environment
Problems Age Environmental stress Physical stress Temperature Humidity
Magnetic Tape
Ribbon of plastic with metallic oxide
Slow
Serial access
Physical wear and tear Tape stretching Physical contact with R/W head
Primarily used for backups
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21. Magnetic Storage Magnetic Disk Drives
Circular platters Magnetic coatings Rotate beneath read/write heads
Track One concentric circle of a platter Data is written
Sector Fractional portion of a track Is the data transfer unit of the device
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22. Optical Mass Storage Devices
Higher Recording density Tightly focused lasers Access very small storage medium area
Longer data life
Not magnetic medium
Data stored as variations in light reflection
Storage medium is a highly reflective material
Read mechanism Low-power laser Photoelectric cell
Laser focused onto one bit at an angle Photoelectric cell at a complementary angle
A highly reflective spot is a one (1) A non reflective spot is a zero (0)
Reflectivity Dints Burned areas Dyes Change from crystalline (fixed shape) to amorphous (shapeless, vague) states
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