Data Storage Elements-Computer Architecture and Programming-Lecture Slides, Slides of Computer Architecture and Organization

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Data StorageMain MemoryMass StorageBinary SystemsStoring IntegersStoring Fractions

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Main Memory Cells^ ^ Cell:

A unit of main memory (typically 8 bits which is one

byte

◦^ Most significant bit:

the bit at the left

(high-order) end of the conceptual row of bitsin a memory cell ◦ Least significant bit:

the bit at the right

(low-order) end of the conceptual row of bitsin a memory cell

Main Memory Addresses^ ^ Address:

A^ “

name

”^

that uniquely identifies

one cell in the computer

’s main memory

◦^ The names are actually numbers. ◦^ These numbers are assigned consecutivelystarting at zero. ◦^ Numbering the cells in this manner associatesan order with the memory cells.

Figure 1.8 Memory cells arranged byaddress

Measuring Memory Capacity^ ^ Kilobyte:

bytes = 1024 bytes

◦^ Example: 3 KB = 3 times1024 bytes ◦^ Sometimes

“kibi

”^ rather than

“kilo

^ Megabyte:

bytes = 1,048,576 bytes

◦^ Example: 3 MB = 3 times 1,048,576 bytes ◦^ Sometimes

megi

”^

rather than

mega

^ Gigabyte:

bytes = 1,073,741,824 bytes

◦^ Example: 3 GB = 3 times 1,073,741,824 bytes ◦^ Sometimes

gigi

”^

rather than

giga

Mass Storage^ ^ On-line versus off-line^ ◦

On-line means that the device or informationis connected and readily available to themachine without human intervention. ◦ Off-line human intervention is required toeither turn on or the medium holding theinformation needs to be inserted.

^ Typically larger than main memory ^ Typically less volatile than main memory ^ Typically slower than main memory

Magnetic Systems^ ^ For years magnetic technology hasdominated the mass storage arena.^ ^ Most common examples of magneticsystems are:^ ◦

Magnetic disk ◦ Magnetic tape

Magnetic Systems(Contd.)^ ^ Magnetic disk:^ ◦

Thin spinning disk with magnetic coating isused to store data. ◦ Read/write heads are placed above and/orbelow the disk. ◦ Each head traverses a circle is called a track. ◦ Each track is than divided into small arcscalled sectors on which information isrecorded.

Magnetic Systems(Contd.)^ ^ Several measurements are used toevaluate a disk system’s performance:^ ◦

Seek time:

the time required to move the

read/write heads from one track to another. ◦ Rotation delay or latency time:

half the

time required for a disk to complete itsrotation ◦ Access time:

the sum of seek time and

rotation delay. ◦ Transfer rate:

the rate at which data can be

transferred to or from the disk.

Magnetic Systems(Contd.)^ ^ Magnetic tape:^ ◦

Information is recorded on the magneticcoating of a thin plastic tape that is wound ona reel for storage. ◦ To access data the tape is mounted in a devicecalled a tape drive. It typically can read, writeand rewind the tape under control of thecomputer. ◦ Major disadvantage is the moving betweendifferent positions on a tape as it can be verytime consuming.

Optical Systems^ ^ Another class of mass storage systemapplies optical technology.^ ^ Common examples are:^ ◦

Compact Disk(CD) ◦ Digital Versatile Disk(DVD)

Optical Systems(Contd.)^ ^ CD:^ ◦

12 cm in diameter and consists of reflectivematerial covered with a clear protectivecoating. ◦ Information is recorded on them by creatingvariations in their reflective surfaces. ◦ CD technology originally applied to audiorecording using a recording format known asCD-DA(compact disk-digital audio).

Optical Systems(Contd.)^ ^ Traditional CD have capacities in range of600-700MB.^ ^ DVDs which are constructed frommultiple semi-transparent layers thatserve as distinct surfaces provide largerstorage capacities of several GB.^ ^ Similarly BDs(Blu-ray Disks) provides5times the capacity of DVD.

Flash Drives^ ^ In flash drive system, bits are stored bysending electronic signals directly to thestorage medium.^ ^ Where they cause electrons to betrapped in tiny chambers of silicondioxide.^ ^ Since these chambers are able to holdtheir captive electrons for many years ,this technology is suitable for off-linestorage of data.