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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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FUNDAMENTALSOFCOMPUTER
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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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MEMORY UNITMEMORY UNIT
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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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MEMORY UNITMEMORY UNIT
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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