MEMORY
Computers don't remember or forget
things the way that human brains do. Computers work in binary
(explained more fully in the box below): they either know something
or they don't—and once they've learned, barring some sort of
catastrophic failure, they generally don't forget. Humans are
different. We can recognize things ("I've seen that face
before somewhere") or feel certain that we know something ("I
remember learning the German word for cherry when I was at school")
without necessarily being able to recollect them. Unlike computers,
humans can forget... remember... forget... remember... making memory
seem more like art or magic than science or technology. When clever
people master tricks that allow them to memorize thousands of pieces
of information, they're celebrated like great magicians—even though
what they've achieved is far less impressive than anything a
five-dollar, USB flash memory stick could do!
1. Primary Memory / Volatile Memory.
2. Secondary Memory / Non Volatile Memory.
In
static RAM, a form of flip flop holds each bit of memory. A flip-flop
for a memory cell takes four or six transistors along with some
wiring, but never has to be refreshed. This makes static RAM
significantly faster than dynamic RAM. However, because it has more
parts, a static memory cell takes up a lot more space on a chip than
a dynamic memory cell. Therefore, you get less memory per chip, and
that makes static RAM a lot more expensive. Static RAM is fast and
expensive, and dynamic RAM is less expensive and slower. Static RAM
is used to create the CPU’s speed sensitive cache, while dynamic
RAM forms the larger system RAM space.
ROM memory has several models such names are following.
1. PROM: Programmable Read Only Memory (PROM) maintains large storage media but can’t offer the erase features in ROM. This type of RO maintains PROM chips to write data once and read many. The programs or instructions designed in PROM can’t be erased by other programs.
2. EPROM : Erasable Programmable Read Only Memory designed for recover the problems of PROM and ROM. Users can delete the data of EPROM thorough pass on ultraviolet light and it erases chip is reprogrammed.
3. EEPROM: Electrically Erasable Programmable Read Only Memory similar to the EPROM but it uses electrical beam for erase the data of ROM.
Cache Memory: Mina memory less than the access time of CPU so, the performance will decrease through less access time. Speed mismatch will decrease through maintain cache memory. Main memory can store huge amount of data but the cache memory normally kept small and low expensive cost. All types of external media like Magnetic disks, Magnetic drives and etc store in cache memory to provide quick access tools to the users.
Magnetic Disks
Speedy access to data, relatively low cost, and the ability to
erase and rewrite data make magnetic disks the most widely used
storage media on today’s computers. With magnetic disk storage
systems, data are written by read/write heads magnetizing the
particles a certain way on a medium surface. The particles retain
their magnetic orientation so they can be read at a later time, and
rewriting to the medium is possible. There are two main types of
magnetic disks:
Since sequential access device means that for n records, where n = 0, 1, 2, 3, ……… if the tape head is positioned at record number 1 then in order to read the nth record, it is necessary to read all the physical records from 1st to nth records one at a time. If the head position is beyond the desired record, it is necessary to rewind the tape for a specific distance and begin reading forward.
In contrast to the magnetic disk, which is a direct access device, a tape is sequential in nature. A disk drive doesn’t read all the sectors on a disk sequentially to get to the desired record, where as magnetic tape drive read all the sectors b/w the starting and the desired location of data. Magnetic tape was the first kind of secondary memory and is still widely used for its lowest cost, however it is very slow in speed than all of the secondary storage devices.
The optical memory devices are:
CD-ROM
Optical disk form of secondary storage that is used to hold prerecorded text, graphics and sound. Like music CDs a CD-ROM is a read-only disk. Read Only means the disk’s content is recorded at the time of manufacture and can not be written on or erased by the user. A CD-ROM disk can hold up to 650 MB of data, equal to 300,000 pages of text.
The DVD represents a new generation of high
density CD-ROM disks, which are read by laser and which have both
write-once and rewritable capabilities. According to the various
industries sponsoring it, DVD stands for either “Digital Video
Disk” or “Digital Versatile Disk”, and it is a CD type disk
with extremely high capacity, able to store 4.7-17 GB.
A very common application of Optical Memory especially CD-ROM is that it can store Multimedia Encyclopedia that contains all 21 volumes of the Academic American Encyclopedia. This encyclopedia comprises full text of about 33000 as well as a comprehensive index of titles, words, pictures and maps. In addition there are thousands of pictures, hundreds of sounds and animations along with dozens of video clips
How memory stores data in binary format???
Photos, videos, text files, or sound, computers store and process all kinds of information in the form of numbers, or digits. That's why they're sometimes called digital computers. Humans like to work with numbers in the decimal (base 10) system (with ten different digits ranging from 0 through 9). Computers, on the other hand, work using an entirely different number system called binary based on just two numbers, zero (0) and one (1). In the decimal system, the columns of numbers correspond to ones, tens, hundreds, thousands, and so on as you step to the left—but in binary the same columns represent powers of two (two, four, eight, sixteen, thirty two, sixty four, and so on). So the decimal number 55 becomes 110111 in binary, which is 32+16+4+2+1. You need a lot more binary digits (also called bits) to store a number. With eight bits (also called a byte), you can store any decimal number from 0–255 (00000000–11111111 in binary).
One reason people like decimal numbers is because we have 10 fingers. Computers don't have 10 fingers. What they have instead is thousands, millions, or even billions of electronic switches called transistors. Transistors store binary numbers when electric currents passing through them switch them on and off. Switching on a transistor stores a one; switching it off stores a zero. A computer can store decimal numbers in its memory by switching off a whole series of transistors in a binary pattern, rather like someone holding up a series of flags. The number 55 is like holding up five flags and keeping one of them down in this pattern
The device you're using when actively working on your computer is the RAM. The RAM is the only storage that has direct access to the central processing unit (CPU), or the brains of your computer, through what is called a bus. The bus is a pathway or circuit that allows the RAM to communicate directly with the CPU to complete the tasks you want accomplished.
That sounds complicated, but what does it really mean? Let's say you arrive at school carrying your book bag and sit down at your empty desk. The empty desk is the RAM, primary memory. As you get ready to study, you take items out of your book bag and place them on the desk. The desk gives you the space you need to get down to business and use your items, such as pencils, folders and books. Just like RAM, the desk serves as the workspace you need to accomplish tasks.
The down side of RAM is that it is volatile. If something happens - say, your computer suddenly shuts down - anything that is stored there is lost. This is why you are constantly told to save your work often - once you save the work from RAM into something more permanent (like your hard drive or a portable storage device), you don't have to worry about losing your work.
Memory is major part of computers that
categories into several types. Memory is best storage part to the
computer users to save information, programs and etc, The computer
memory offer several kinds of storage media some of them can
store data temporarily and some them can store permanently. Memory
consists of instructions and the data saved into computer through
Central Processing Unit (CPU).
Computers don't remember or forget
things the way that human brains do. Computers work in binary
(explained more fully in the box below): they either know something
or they don't—and once they've learned, barring some sort of
catastrophic failure, they generally don't forget. Humans are
different. We can recognize things ("I've seen that face
before somewhere") or feel certain that we know something ("I
remember learning the German word for cherry when I was at school")
without necessarily being able to recollect them. Unlike computers,
humans can forget... remember... forget... remember... making memory
seem more like art or magic than science or technology. When clever
people master tricks that allow them to memorize thousands of pieces
of information, they're celebrated like great magicians—even though
what they've achieved is far less impressive than anything a
five-dollar, USB flash memory stick could do!
Types of Computer Memory:
Memory is the best essential element of a computer because computer can’t perform simple tasks. The performance of computer mainly based on memory and CPU. Memory is internal storage media of computer that has several names such as majorly categorized into two types, Main memory and Secondary memory.1. Primary Memory / Volatile Memory.
2. Secondary Memory / Non Volatile Memory.
1. Primary Memory / Volatile Memory:
When many people hear the term 'primary storage,' they think of the hard drive on the computer - where you store or save your data. But primary storage is actually where the data you are actively using is being stored. In other words, whatever you are working on at the moment is being held in primary storage. Primary Memory also called as volatile memory because the memory can’t store the data permanently. Primary memory select any part of memory when user want to save the data in memory but that may not be store permanently on that location. It also has another name i.e. RAM.Random Access Memory (RAM):
The primary storage is referred to as random access memory (RAM) due to the random selection of memory locations. It performs both read and write operations on memory. If power failures happened in systems during memory access then you will lose your data permanently. So, RAM is volatile memory. RAM categorized into two types.- Static RAM
- Dynamic RAM
Dynamic
RAM : loses its stored information in a very short time (for milli
sec.) even when power supply is on. D-RAM’s are cheaper &
lower.
Similar
to a microprocessor chip is an Integrated Circuit (IC) made of
millions of transistors and capacitors.
In
the most common form of computer memory, Dynamic Memory Cell,
represents a single bit of data. The capacitor holds the bit of
information – a 0 or a 1. The transistor acts as a switch that lets
the control circuitry on the memory chip read the capacitor or change
its state. A capacitor is like a small bucket that is able to store
electrons. To store a 1 in the memory cell, the bucket is filled with
electrons.
To
store a 0, it is emptied. The problem with the capacitor’s bucket
is that it has a leak. In a matter of a few milliseconds a full
bucket becomes empty. Therefore, for dynamic memory to work, either
the CPU or the Memory Controller has to come along and recharge all
of the capacitors holding it before they discharge. To do this, the
memory controller reads the memory and then writes it right back.
This refresh operation happens automatically thousands of times per
second.
This
refresh operation is where dynamic RAM gets its name. Dynamic RAM has
to be dynamically refreshed all of the time or it forgets what it is
holding. The downside of all of this refreshing is that it takes time
and slows down the memory.
Static
RAM uses a completely different technology. S-RAM retains stored
information only as long as the power supply is on. Static RAM’s
are costlier and consume more power. They have higher speed than
D-RAMs. They store information in Hip-Hope.
In
static RAM, a form of flip flop holds each bit of memory. A flip-flop
for a memory cell takes four or six transistors along with some
wiring, but never has to be refreshed. This makes static RAM
significantly faster than dynamic RAM. However, because it has more
parts, a static memory cell takes up a lot more space on a chip than
a dynamic memory cell. Therefore, you get less memory per chip, and
that makes static RAM a lot more expensive. Static RAM is fast and
expensive, and dynamic RAM is less expensive and slower. Static RAM
is used to create the CPU’s speed sensitive cache, while dynamic
RAM forms the larger system RAM space.
EDO
(Extended Data Output) RAM :
In an EDO RAMs, any memory location can be accessed. Stores 256 bytes
of data information into latches. The latches hold next 256 bytes of
information so that in most programs, which are sequentially
executed, the data are available without wait states.
SDRAM
(Synchronous DRAMS),
SGRAMs (Synchronous Graphic RAMs) These RAM chips use the same clock
rate as CPUuses. They transfer data when the CPU expects them to be
ready.
DDR-SDRAM
(Double Data Rate – SDRAM) :
This RAM transfers data on both edges of the clock. Therefore the
transfer rate of the data becomes doubles.
ROM
:
Read only memory: Its non volatile memory, ie, the information stored
in it, is not lost even if the power supply goes off. It’s used for
the permanent storage of information. It also posses random access
property. Information can not be written into a ROM by the
users/programmers. In other words the contents of ROMs are decided by
the manufactures.
The
following types of ROM
(i)
PROM :
It’s programmable ROM. Its contents are decided by the user. The
user can store permanent programs, data etc in a PROM. The data is
fed into it using a PROM programs.
(ii)
EPROM :
An EPROM is an erasable PROM. The stored data in EPROM’s can be
erased by exposing it to UV light for about 20 min. It’s not easy
to erase it because the EPROM IC has to be removed from the computer
and exposed to UV light. The entire data is erased and not selected
portions by the user. EPROM’s are cheap and reliable.
(iii)
EEPROM (Electrically Erasable PROM) :
The chip can be erased & reprogrammed on the board easily byte by
byte. It can be erased with in a few milliseconds. There is a limit
on the number of times the EEPROM’s can be reprogrammed, i.e.;
usually around 10,000 times.
Flash
Memory :
Its an electrically erasable & programmable permanent type
memory. It uses one transistor memory all resulting in high packing
density, low power consumption, lower cost & higher reliability.
Its used in all power, digital cameras, MP3 players etc.
2. Secondary Memory / Non Volatile Memory:
Secondary memory is external and permanent memory that is useful to store the external storage media such as floppy disk, magnetic disks, magnetic tapes and etc cache devices. Secondary memory deals with following types of components. This is also called Mass Storage, Auxiliary Memory and External Memory. This memory is slower than the Main memory as it involves mechanical motion techniques during storage and retrieval of data. This memory is larger in size than Main memory but the processor is unable to access it directly due to its offline link with the processor. This means that the data from secondary storage must be loaded into RAM before the processor starts processing it. The main memory links the secondary memory to the processor.Read Only Memory (ROM) :
ROM is permanent memory location that offer huge types of standards to save data. But it work with read only operation. No data lose happen whenever power failure occur during the ROM memory work in computers.ROM memory has several models such names are following.
1. PROM: Programmable Read Only Memory (PROM) maintains large storage media but can’t offer the erase features in ROM. This type of RO maintains PROM chips to write data once and read many. The programs or instructions designed in PROM can’t be erased by other programs.
2. EPROM : Erasable Programmable Read Only Memory designed for recover the problems of PROM and ROM. Users can delete the data of EPROM thorough pass on ultraviolet light and it erases chip is reprogrammed.
3. EEPROM: Electrically Erasable Programmable Read Only Memory similar to the EPROM but it uses electrical beam for erase the data of ROM.
Cache Memory: Mina memory less than the access time of CPU so, the performance will decrease through less access time. Speed mismatch will decrease through maintain cache memory. Main memory can store huge amount of data but the cache memory normally kept small and low expensive cost. All types of external media like Magnetic disks, Magnetic drives and etc store in cache memory to provide quick access tools to the users.
Magnetic Disks
Speedy access to data, relatively low cost, and the ability to
erase and rewrite data make magnetic disks the most widely used
storage media on today’s computers. With magnetic disk storage
systems, data are written by read/write heads magnetizing the
particles a certain way on a medium surface. The particles retain
their magnetic orientation so they can be read at a later time, and
rewriting to the medium is possible. There are two main types of
magnetic disks:
Floppy Disk:
Floppy Disk is a round, flat piece of Mylar coated with ferric oxide, rust like substance containing tiny particles capable of holding a magnetic field, and encased in a protective plastic cover, the disk jacket. Data is stored on a floppy disk by the disk drive's read/write head, which alters the magnetic orientation of the particles. Orientation in one direction represents binary 1; orientation in the other, binary 0. Typically, a floppy disk is 5.25 inches in diameter, with a large hole in the center that fits around the spindle in the disk drive. Depending on its capacity, such a disk can hold from a few hundred thousand to over one million bytes of data. A 3.5-inch disk encased in rigid plastic is usually called a microfloppy disk but can also be called a floppy disk.Hard Disk:
Hard Disk composed of one or more platters that are permanently sealed within a hard metallic casing. These hard disks are fixed in the computer CPU and are seldom transferred from one computer to another. For the better use of the hard disk space, a hard disk can be divided into any number of partitions like C: D: E: etc. however making too many partitions is not a good management practice for the memory of hard disk.Now days up to 2000 GB hard disks are available in the market. For the better use of disk space a hard disk can be divided into a number of partitions like C: D: E: etc.Magnetic Tapes:
Magnetic tape and the tape drives are analogous to a home tape recorder system. It uses the same reading and recording techniques as that of the magnetic disk as the medium used in it is a flexible tape that is coated with magnetic oxide.Since sequential access device means that for n records, where n = 0, 1, 2, 3, ……… if the tape head is positioned at record number 1 then in order to read the nth record, it is necessary to read all the physical records from 1st to nth records one at a time. If the head position is beyond the desired record, it is necessary to rewind the tape for a specific distance and begin reading forward.
In contrast to the magnetic disk, which is a direct access device, a tape is sequential in nature. A disk drive doesn’t read all the sectors on a disk sequentially to get to the desired record, where as magnetic tape drive read all the sectors b/w the starting and the desired location of data. Magnetic tape was the first kind of secondary memory and is still widely used for its lowest cost, however it is very slow in speed than all of the secondary storage devices.
Features
Secondary Storage is magnetic in nature and therefore magnetic mechanisms are used to store data permanently. Data or information is stored in the form of files. A file is an area of the secondary memory where data or information is permanently stored. Each file has its unique file name through which it is accessed. The storage of data in secondary memory follows some file organization techniques such as Sequential, Indexed Sequential and Random/Direct access file organizations. Sequential access file organization is adopted for Magnetic Tape while Random/Direct access file organization is more suitable for Hard Disk or Floppy Disk.Advantages:
- Data remains permanently stored even when the computer is switched off.
- This data remains in the memory until deleted by the computer user.
- Very high volumes of data can be recorded for long time and is updated and retrieved efficiently.
- Transfer of data from one computer to another is performed through this memory like through Floppy or CDs.
- System files associated with any Operating System are permanently stored in this memory. These files are loaded into RAM at the time of booting the computer system.
- To prevent any damage and loss of data,
Backup and Recovery procedures are facilitated through Secondary
Memory.
Optical Memory
Optical memory is used for storing large volumes of data like sound, text, graphics, and videos. An optical disk is a removable disk that uses laser to read and write data. With an optical disk, there is no mechanical arm, as with floppy disks and hard disks. Instead a high-power laser beam is used to write data by burning tiny pits into the surface of a hard plastic disk. To read the data, a low-power laser light scans the disk surface: pitted areas are not reflected and are interpreted as 0 bits; smooth areas are reflected and are interpreted as 1 bits. Because the pits are so tiny, a great deal more data can be represented than is possible in the same amount of space on hard disks. An optical disk can hold over 4.7 gigabytes of data, the equivalent of 1 million type-written pages.The optical memory devices are:
Compact Disk (CD)
CD is a non-erasable disk that stores the digitized audio information. The standard system uses 12 cm disks and they can record more than 60 minutes of playing time without any interruption.CD-ROM
Optical disk form of secondary storage that is used to hold prerecorded text, graphics and sound. Like music CDs a CD-ROM is a read-only disk. Read Only means the disk’s content is recorded at the time of manufacture and can not be written on or erased by the user. A CD-ROM disk can hold up to 650 MB of data, equal to 300,000 pages of text.
CR-RW
CD-RW (Compact Disk-Rewritable) also called as Erasable Optical Disk allow users to record and erase data so that the disk can be used over and over again. Special CD-RW drives and software is required.DVD (Digital Versatile Disk) : the “Digital Convergence” Disk
DVD-R
DVD disks that allow one time recording by the consumer. Two types of reusable disks are DVD-RW (DVD Rewritable) and DVD-RAM (DVD Random Access Memory), both of which can be recorded on and erased more than once.Write Once Read Many (WORM)
WORM is a disk that is more easily written than CD-ROM thus making single copy disks commercially feasible. After performing the write operation the disk is read only. The most popular size is 51/4 “that can hold data from 200 to 800 MB.Magneto-Optical Disk
There are a few other types of storage systems that use a combination of magnetic and optical technology – the magneto-optical disk is one of them. M-O disks can store up to 5.2 GB of data.A very common application of Optical Memory especially CD-ROM is that it can store Multimedia Encyclopedia that contains all 21 volumes of the Academic American Encyclopedia. This encyclopedia comprises full text of about 33000 as well as a comprehensive index of titles, words, pictures and maps. In addition there are thousands of pictures, hundreds of sounds and animations along with dozens of video clips
How memory stores data in binary format???
Photos, videos, text files, or sound, computers store and process all kinds of information in the form of numbers, or digits. That's why they're sometimes called digital computers. Humans like to work with numbers in the decimal (base 10) system (with ten different digits ranging from 0 through 9). Computers, on the other hand, work using an entirely different number system called binary based on just two numbers, zero (0) and one (1). In the decimal system, the columns of numbers correspond to ones, tens, hundreds, thousands, and so on as you step to the left—but in binary the same columns represent powers of two (two, four, eight, sixteen, thirty two, sixty four, and so on). So the decimal number 55 becomes 110111 in binary, which is 32+16+4+2+1. You need a lot more binary digits (also called bits) to store a number. With eight bits (also called a byte), you can store any decimal number from 0–255 (00000000–11111111 in binary).
One reason people like decimal numbers is because we have 10 fingers. Computers don't have 10 fingers. What they have instead is thousands, millions, or even billions of electronic switches called transistors. Transistors store binary numbers when electric currents passing through them switch them on and off. Switching on a transistor stores a one; switching it off stores a zero. A computer can store decimal numbers in its memory by switching off a whole series of transistors in a binary pattern, rather like someone holding up a series of flags. The number 55 is like holding up five flags and keeping one of them down in this pattern
WHY WE NEED RAM IN CPU???
The device you're using when actively working on your computer is the RAM. The RAM is the only storage that has direct access to the central processing unit (CPU), or the brains of your computer, through what is called a bus. The bus is a pathway or circuit that allows the RAM to communicate directly with the CPU to complete the tasks you want accomplished.
That sounds complicated, but what does it really mean? Let's say you arrive at school carrying your book bag and sit down at your empty desk. The empty desk is the RAM, primary memory. As you get ready to study, you take items out of your book bag and place them on the desk. The desk gives you the space you need to get down to business and use your items, such as pencils, folders and books. Just like RAM, the desk serves as the workspace you need to accomplish tasks.
The down side of RAM is that it is volatile. If something happens - say, your computer suddenly shuts down - anything that is stored there is lost. This is why you are constantly told to save your work often - once you save the work from RAM into something more permanent (like your hard drive or a portable storage device), you don't have to worry about losing your work.
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