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Technology 1
Secondary Storage
CS1251Computer Organization
Carl Hamacher
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Virtual Memory (VM)
Processor address space greater than physical main
memory (RAM)
32-bit address = 4G bytes
Secondary storage (magnetic disk)
Virtual (logical) addresses translated into physical
addresses
Memory Management Unit (MMU)
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VM Organization
Processor
Cache
Main Memory
Disk Storage
MMU
Virtual Address
Physical Address
Physical Address
DMA Transfer
Data
Data
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Cache vs. Virtual Memory
Cache Memory
Bridges speed gap between processor and main memory
Implemented in hardware
Virtual Memory Bridges size and speed gaps between main memory and
secondary storage
Implemented (in part) by software (operating system)
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VM Address Translation
Pages
Fixed-length units
Blocks of words that occupy contiguous
locations in main memory
Commonly 2K to 16K bytes
Too smallmore (slow) accesses
Too largeunnecessary info in main memory
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VM Address Translation
Virtual Page Number
High-order bits
Which page
Offset Low-order bits
Word within page
Control Bits
Validity
Modification
Restrictions (read/write)
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VM Address Translation
Page Table
Info about main memory location of each page
Kept in main memory
MMU cache for most recently accessed pages Page Frame
Area of main memory that can hold one page
Page Table Base Register
Starting address of page table
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VM Address Translation
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Memory Management
Operating System
System Space
Supervisor State
Privileged Instructions Application Programs
User Space
User State
Protection
No program should be allowed to destroy either data or
instructions of another program
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Magnetic Hard Disks
Phase Encoding (Manchester Encoding)
Change in magnetization guaranteed at midpoint of each
bit
Provides clocking info for synchronization Other self-clocking schemes
More efficient
Better storage density
More complex control circuitry
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Hard Disk Components
Disk
Assembly of disk platters
Disk Drive
Electromechanical system Spins disk
Moves read/write heads
Disk Controller
Electronic circuitry
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Hard Disk Organization
Organization of data
Concentric tracks
Divided into sectors
Divided into logical partitions Formatting
Divides disk into tracks and sectors
Excludes defective sectors
About 15% overhead
Sector headers
Error-correction codes
Intersector gaps
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Access Time
Seek Time
Time required to move the read/write head to the proper
track
Latency Time Rotational delay
Time until head is over correct track
Times measured in ms
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Disk Controller
Data Buffer
Difference in transfer rates between disk and bus
Also serves as a disk cache
Read/Write Requests Main memory addressdisk address
Word count
Booting
OS loaded into main memory
Nonvolatile ROM stores monitor program
Boot block with loader program
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RAID
Redundant Array of Inexpensive Disks
RAID 0
Performance enhancement
Single large file stored in several separate disk units Disks deliver data in parallel
RAID 1
Relaibility
Storing identical copies of data on two disks
Mirror
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RAID
RAID 2, RAID 3, RAID 4
Reliability
Various parity checking schemes
RAID 5 Reliability
Parity-based error-recovery scheme
Distributed across disks
RAID 10
Performance and reliability
Hybrid of RAID 0 and RAID 1
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Optical Disks
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CD vs. DVD
Compact Disk (CD)
CD-ROM
CD-R
CD-RW Digital Versatile Disk (DVD)
Shorter wavelength laser
Smaller focus, smaller pits, closer tracks
Capacity
CD = 800 MB
DVD = 4.7 GB
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Magnetic Tape Systems
Off-line storage of large amounts of data
Back-up and archival storage
Data organized into records and files
Highest capacity
Slowest
Cheapest
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Memory Hierarchy
Processor
Registers
Primary Cache
Secondary Cache
Main Memory
Secondary Memory
Increasing
Size
Increasing
Speed
Increasing
Cost
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Questions?
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