Computer Memory
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Transcript of Computer Memory
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Topics
History of memoryMemory Types of memory
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History of memory
In the early 1940s, memory technology mostly permitted a capacity of a few bytes.
ENIAC(Electronic Numerical Integrator And
Computer): Firs electronic general-purpose computer . That is capable of being reprogrammed to solve a large class of numerical problems.
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Vacuum tubes.The first electronic programmable digital computer the ENIAC, using thousands of octal-base radio vacuum tubes could perform simple calculations involving 20 numbers of ten decimal digits
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delay line memory:
developed by J. Presper Eckert in the early 1940s.
It is also used in digital computers. Delay line memory would be limited to a
capacity of up to a few hundred thousand bits to remain efficient.
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random access computer memory
the Williams tube and Selectron tube originated in 1946.
in 1947 Jay Forrester, Jan A. Rajchman and An Wang developed magnetic core memory which allowed for recall of memory after power loss.
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random access computer memory.
the Selectron was limited to 256 bits, while the Williams tube could store thousands
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Magnetic core memory
•It was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.
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Memory
.
Electronic components that store instructions, data, and results
Consists of one or more chips on motherboard orother circuit board
Each byte stored in unique location called an address.
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Memory
It holds the data and instructions that the Central Processing Unit (CPU) needs.
Before a program can be run the program is loaded from the storage medium into memory.
It allows the CPU to direct interact with the program.
Memory is a need of every computer
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Memory
Memory chips almost always come as part of a card called a module.
Memory's usually listed with two numbers, such as 8x32 or 4x16.
The first number represents the number of chips on the module.
The second one tells the capacity of each individual chip, measured in megabits (Mb), or one million bits.
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Types of memory
1.ROM (Read Only Memory) 2.RAM (Random Access Memory)3.Cache4.Flash memory
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ROMstores data without electrical current; it is the ROM (Read Only Memory)
or is sometimes called non-volatile memory as it is not erased when the system is switched off
Read Only Memory
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Types of ROM
PROM (Programmable Read Only Memory)EPROM (Erasable Programmable Read Only
Memory)EEPROM (Electrically Erasable Read Only
Memory .
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PROM
Programmable read-only memory (PROM) is a blank ROM chip on which a programmer can write permanently, but once written cannot be changed or modified
ROM cannot be written when the computer is running.
ROM use for important program like BIOS or the firmware of a device.
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PROM.
Once a program has been written onto a PROM, it remains there forever.
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But most ROM chips designed to be modified by users, use
Erasable programmable read-only memory ( EPROM) or electrically erasable programmable
read-only memory ( EEPROM).
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EPROM
An EPROM or erasable programmable read
only memory, is a type of memory chip
Once programmed, an EPROM can be erased with the help of ultraviolet light
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EEPROM
Electrically Erasable Programmable Read-Only Memory
Type of PROM that can be erased by exposing it to an electrical charge.
Similar to EPROM.
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Memory
How is memory measured?
Term Abbreviation Approximate Size
Kilobyte KB or K 1 thousand bytes
Megabyte MB 1 million bytes
Gigabyte GB 1 billion bytes
Terabyte TB 1 trillion bytes
By number of bytes available for storage
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RAM
Random Access Memory, can be accessed randomly. Any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.
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Memory
What is random access memory (RAM)?
p. 195
The more RAM a The more RAM a computer has, the computer has, the faster it respondsfaster it responds
Also called Also called main memorymain memory
or or primary primary storagestorage
Most RAM is Most RAM is volatilevolatile, it is lost , it is lost when computer’s when computer’s
power is power is turned offturned off
Memory chips that can be Memory chips that can be read from and written read from and written
to by processorto by processor
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RAM
RAM is mostly sold in multiples of 16 megabytes: 16, 32, 64, 128, 256, 512 and 1,024 (the same as 1GB) .
DDR2 and DDR3 RAMs.DDR2Appears in 2004 (speed: delivering
bandwidth of up to 8.5 GB per second)DDR3Appears in 2007(speed : can transfer data at
rates up to 12.8 GB per second)
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DDR2DDR2 DDR3DDR3
RAMs
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Types of RAM
There are two different types of RAM: DRAM (Dynamic Random Access Memory) SRAM (Static Random Access Memory).DRAM: Needs to be refreshed thousands of times per
second while.Dynamic RAM needs to automatically refresh
thousands of times per second; that's where it gets the name dynamic. Otherwise, it will forget the information it's holding.
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DRAM
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SRAMDoes not need to be refreshed, which is what makes it faster than DRAM.
Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.
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Memory
Where does memory chips reside?
Memory slots on motherboard hold memory modules
memory chip memory slot
dual inline memory module
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Cache memory
Helps speed computer processes by storing frequently used instructions and data
The cache is a smaller, faster memory which stores copies of the data from frequently used main memory locations.
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Cache memory
When the processor needs to read from or write to a location in main memory, it first checks whether a copy of that data is in the cache. If so, the processor immediately reads from or writes to the cache, which is much faster than reading from or writing to main memory.
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Flash Memory
Non volatile memory can be erased electronically and rewritten similar to EEPROM.
Introduced by Toshiba in 1984Most computers use it to hold up their
startup instructionsAlso used in many mobiles , smart phones , digital cameras and PDA
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Flash memory
There are two main types of flash memory.1. NAND2.NOR NAND type flash memory may be written
and read in blocks. NOR type flash allows a single machine
word(byte) to be written to an erased location or read independently.
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What is capacity
.
Kilobyte (KB) 1 thousand
Megabyte (MB) 1 million
Gigabyte (GB) 1 billion
Terabyte (TB) 1 trillion
Petabyte (PB) 1 quadrillion
Number of bytes (characters) a storage medium can hold
Exabyte (EB) 1 quintillion
Zettabyte (ZB) 1 sextillion
Yottabyte (YB) 1 septillion
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Memory
Smallest unit: bit8 bit = 1 byte 1024 byte = 1 kb (kilo byte)Each byte is able to represent 255 different
number (0 to 255)
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