09 Memory Units Rajon

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MEMORY UNITMEMORY UNIT

COURSE TEACHER

S. A. AHSAN RAJONS. A. AHSAN RAJON

Computer Science and Engineering Discipline,Khulna University, Khulna.

E-Mail: [email protected]

Web: www.rajon.forumerzone.com
mailto:[email protected]://www.rajon.forumerzone.com/http://www.rajon.forumerzone.com/mailto:[email protected]


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FLASHBACKFLASHBACK


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Units of MeasurementUnits of Measurement

Everything in a computer is stored as

combination of 1s and 0s.

A bit can be a 1 or a zero

1 byte = 8 bits

1 kilobyte = 1 024 bytes

1 megabyte = 1 048 576 bytes

1 gigabyte = 1 073 741 824 bytes


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Standard ComputerStandard Computer

Von Neumann

Architecture

Single processing unit

Separate storage unit

to hold instructionsand data


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BIOSBIOS

Chip containing basic

software that is usedto boot up thecomputer.

Prepares the machine

so that other softwareprograms stored onthe hard drive andelsewhere can loadand assume control ofthe PC.

Software can beinteracted with via theBIOS screen.


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MAIN BOARDMAIN BOARD

Motherboard

Ties all the different

components together.

Generally offers

networking hardware,some basic graphics

and sound, etc.


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MEMORYMEMORY

Memory may be defined as the devices

which is used to storedata and

information.

Memory components of a computer system

are divided into three groups-Main Memory or Primary Memory

Secondary Memory or Auxiliary Memory or

Back-up MemoryInternal Processor Memory


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MEMORYMEMORY

Main Memory or Primary memory

Characterized by the fact that, locations in mainmemory can be directly accessed by the CPUinstruction set.

Used for program and data storage duringcomputer OPERATION

Secondary Memory or Auxiliary Memory or Back-Up memoryMuch larger in size but much slowerthan memory.Used for storing system program and large data

files which are continually not required by CPU Internal Processor Memory

Usually comprise ofsmall set of high speedregisters used as working registers for temporarystorage of instructions and data.


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MEMORY: DO WE NEED ??MEMORY: DO WE NEED ??

To store program and

data during execution To Store program for

repetitive use

To Store data forfuture or periodical

use.

To Store results for

execution.


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MAIN MEMORYMAIN MEMORY BIT?

BYTE? MEGABYTE ? GIGABYTE ? TERABYTE ?

NIBBLE: 4 bits

WORD:Unit of bits that a computer can process at a time.Set of bits processed by microprocessor as a unit.32-bit computer ?? Word-length = 32 ???

A 1KB computer storage has exactly 1024 storage locationstypically presented as 0000 to 1023.

A computer with 64K storage has 64536 storage locations inmemory.

1 MB is roughly 1 Million (Exactly, 220)bytes of storage. Roughly 1GB has 1 Billion bytes of storage. Roughly 1TB has 1 Trillion bytes of storage.


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MAIN MEMORYMAIN MEMORY

Two kinds of main memory are commonly

used in modern computers.

Semiconductor Memory

Magnetic Memory


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TERMINOLOGIESTERMINOLOGIES

Memory Access

Instructions or data are read from or written into the memoryone word at a time.

Reading from the memory or writing data into memory is

usually called MEMORY ACCESS.

ACCESS TIME

The performance of a memory device is primarily determined

by the rate at which information i.e. one word from the

memory is read/written. Known as Access Time.

OR

OR

OR

220 bytes

216 bytes

210 bytes

201MB

1664KB

101KB

NUMBER OF BITS NEEDED TO ADDRESSMEMORY CAPACITY


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TYPES OF MEMORYTYPES OF MEMORY

VOLATILE MEMORY

If stored information is destroyed when

power goes off.

NON-VOLATILE MEMORY

Stored information is preserved when

power goes off or power failure.

Most Semi-conductor Memory (RAM) Volatile Magnetic Memory (disk) NonVolatile


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SERIAL ACCESS MEMORY

storage locations can be accessed in only incertain pre-defined sequence

RANDOM ACCESS MEMORY (RAM)

If memory locations can be accessed in any orderand access time is independent of the locationbeing accessed, the memory is called RandomAccess Memory.E.g. ferrite core and semiconductor memories.

Categorized as Static RAM

Dynamic RAM


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STATIC RAMSTATIC RAM

Static RAM (SRAM)

Made up of flip flop

Stores bit as voltage High 1, Low 0Designed using Bipolar Transistors

Need no refreshing

Require greater power supply

Four times larger in area

Contain less data


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DYNAMIC RAMDYNAMIC RAM

Dynamic RAM (DRAM)

Made up of MOS transistors

Stores Bit as charge in capacitors;

presence of charge 1, else 0High density and low power consumptionsCharge is leaked; require refreshing; read

data from the capacitor and write it back

periodically.Smaller area


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ROMROM

READ ONLY MEMORY

There are some random access memories in whichdata are permanently recorded during fabricationitself.

The memory only allows information stored into itto be read and would not permit any writing or

modification by users.All microcomputers have at least one ROM unit that

contains a small program called BOOTSTRAPLOADER.

This program is automatically copied into primary

storage when a computer is powered up and beingto execute. This program is responsible for reading in a copy

of the operating system from a secondary storagedevice.


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Here is a schematic


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PROMPROM

PROGRAMMABLE READ ONLY MEMORY

Nichrome or Polysilicon wires arranged in a

matrix.

These wires can be viewed functionally as

diodes or fuses.The memory can be programmed by the

special PROM programmer that selectively

burns the fuses according their bit pattern

to be stored.

This is called burning the PROM and the

info stored is permanent.


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EPROMEPROM

ERASABLE PROGRAMMABLE READ ONLY

MEMORY

Stores bit by charging floating of FET.

Applies high voltages to charge the gate

All the info erased by exposing the chip toUltra-violate Light (UV Ray) through Quartz

window.

The chip can be reprogrammed.Useful for labs / Experiments because can

be reused again.


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E-EPROME-EPROM

ELECTRONICALLY ERASABLE

PROGRAMMABLE READ ONLY MEMORYUsed vastly in remote control applications.Erased using computers 10ms to erase a total chipAny specific part may be altered by which is the

most important point. Information can be altered using electrical signals

at register levels rather than erasing all the info.Software updates may be done for the EEPROM

using devices from remote link via telephone lines. In Chip erase mode, entire chip can be erased in 10

ms to 15 ms whereas it takes 15 to 20 mins to eraseEPROM.


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MAGNETIC CORE STORAGEMAGNETIC CORE STORAGE

A ring of iron oxide

(ferrite),magnetized by acurrent through awire, the directionof whichdetermines thedirection ofmagnetism(polarity) in the

core. When currentis removed, thecore remainsmagnetized.

1 0


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MAGNETIC CORE STORAGEMAGNETIC CORE STORAGE

If a core is magnetized in one direction and

a current ispassed through the core from

the other direction, the core changes its

state.

In doing so it produces s detectable kick.


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SEMICONDUCTOR STORAGESEMICONDUCTOR STORAGE

Virtually all computers made today have semiconductor

elements in their memory. Typical semiconductor memory consists of a rectangular

array of memory cell. Basic semiconductor memory cell is transistor or a circuit

capable ofstoring charge and is used to store 1 bit ofinformation.

Metal Oxide Semiconductor (MOS) is used for makingcomputers main memory chip.

Chip is a term used to refer to a semiconductor memorydevice having a silicon base.

Electronic circuit which consists of a collection of differentcomponents like transistors, resistors, capacitors is knownas integrated circuit (IC)and that is fabricated on a single chipfrom a memory device.


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COMPARISON: MOS vs. CORECOMPARISON: MOS vs. CORE

Core memory has to be assembled manually

whereas MOS memory can be producedmechanically. Hence MOS memory is cheaperthan core memory.

MOS memory is available on a miniaturized chipand is therefore much smaller in size than corememory

Core memory has a destructive read operation,while MOS memory has a non-destructive readoperation. This enhances the speed of MOS(Chip) Memory.


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COMPARISON: MOS vs. CORECOMPARISON: MOS vs. CORE

MOS memory is volatile, whereas core

memory is non-volatile.

Core memory is available only in large

blocks whereas MOS memory is availablein wide variety of sizes up to 65 Kbytes.

Core memory has limited range of cycle

and access time whereas MOS memory haswide range of cycle and access time andfaster than core memory.


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SECONDARY MEMORYSECONDARY MEMORY

Much larger in capacity

Magnetic Tape

Magnetic Disk

Floppy Disk

Optical Disk

Three common characteristics

Non-Volatile Storage

Cost-Efficiency

Optical Disk


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PRIMARY VS SECONDARY MEMORYPRIMARY VS SECONDARY MEMORY

Outside but connected

to CPUWithin CPULOCATION

Magnetic Tape/ DiskSemiconductormagnetic core

STORAGE MEDIA

Data must be routed

through the primary

storage

Directly accessible to

the processing unitPROCESSING

Millionth of secondBillionth of secondACCESS TIME

Nearly LimitedLimitedCAPACITY

Less expensiveExpensiveCOST

SECONDARY

MEMORY

PRIMARY MEMORY


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Storage Hierarchy LadderStorage Hierarchy Ladder

Storage Hierarchy Ladder

REGISTERSCACHE

MAIN MEMORY

MAGNETIC DISK

MAGNETIC TAPE | OPTICAL DISK


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SELF STUDYSELF STUDY

SELF STUDY

Magnetic Tape

Magnetic Disk

Optical Disk

Magnetic Bubble


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09 Memory Units Rajon

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