CIM101 : Introduction to CIM101 : Introduction to computercomputerLecture 3Lecture 3MemoryMemory

Devices that uses Devices that uses memorymemorySee

MemoryMemory Computer memory refers to devices that are

used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer.

refer to the semiconductor technology that is used to store information in electronic devices. Current primary computer memory makes use of integrated circuits consisting of silicon-based transistors.

There are two main types of memory: volatile and non-volatile.

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Types of Computer Types of Computer MemoryMemory

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Volatile memoryVolatile memory

Volatile memory is computer memory that requires power to maintain the stored information.

Current semiconductor volatile memory technology is usually either static RAM (see SRAM) or dynamic RAM (see DRAM).

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Non-volatile memoryNon-volatile memory

Non-volatile memory is computer memory that can retain the stored information even when not powered.

Examples :read-only memory ( ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape and punch cards.

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Classification based on Classification based on access time access time 1. Internal processor memory

(called registers).2. Main memory (primary memory).

1. Uses semiconductor technology. 2. Capacity more than processor

memory.

3. Secondary memory. 1. Capacity more than main memory.

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Properties of memory Properties of memory devicesdevices

Access time:◦Rate at which data can be read from

or written to memory.◦Depends on physical characteristics.◦Low access time means high cost.

Punch card

CD-ROM

Magnetic Disks

RAM

COSTAccess Time

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Cost◦The purchase price.

Access mode◦Random access(access time

independent of loc)◦Serial access (access time dependent of

loc)Alterability

◦Read-only (ROM). Can not be erased.◦Read-write (RAM).

Cycle time & data transfer rate◦Time needed to perform any read or

write task.◦Maximum amount of data that can be

transferred every second. (bits/sec)04/20/23 10

Physical characteristics◦Technology used to store data.◦The popular technologies are

electronic, magnetic, mechanical and optical.

Capacity◦The number of 0’s and 1’s the

memory can hold.◦Bit(Binary Digit).◦Byte (= 8 bits).◦Kilobyte (= 1024 bytes or 2^10 byte).

KB.◦Megabyte (= 1024 KBs). MB.

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Memory HierarchiesMemory Hierarchies

Microprocessor

Register

Built in cache

External Cache

Main Memory

Secondary Memory

Cost per bit

Access time 04/20/23 12

CapacityCapacity

Read Only MemoryRead Only MemoryROM

◦Used to store permanent data/program.

◦ nonvolatile.◦Contains the BIOS(Basic Input Output

System).PROM( Programmable ROM)

◦Initially nothing stored.◦Data written by special programming

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Read Only MemoryRead Only Memory

EPROM( Erasable Programmable ROM)◦ Can be erased and re-programmed.◦ Ultraviolet light is used for alteration.◦ Need special programming device

EEPROM(Electrically EPROM)◦ Same as EPROM◦ Uses electrical pulses for alteration.◦ Can be re-programmed by keyboards

commands

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RAMRAMRead/write.Volatile.Holds data and program that will be used

by the processor.Access time (microseconds to nanosecs).MOS and bipolar are used for RAM.A single RAM chip can be 1 MB.Higher capacity RAMs are built by

connecting more than 1 RAM chip

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RAMRAM

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ClassificationClassificationStatic

◦Does not require refreshing.◦High speed, costly, less complexity,

used for cache.Dynamic

◦Needs periodical refreshing.◦Slower, low cost, main memory, high

complexity.

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Cache MemoryCache MemoryUsed for better performance.Placed between CPU and RAM.Its faster than RAM but slower

than CPU.High speed memory that holds

recently/frequently used data.

CPU CacheMain Memory

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