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ROM (Read Only Memory)
 Concept:
 Is read-only memory.
 Do not lose data when power is lost.
 ROM memory is used to produce chips with integrated CMOS
BIOS program
 Characteristics of the ROM BIOS
 BIOS ROM containing the software configuration and system
diagnostics, and routine input / output low level that DOS uses.
 These programs are encoded in ROM and is called firmware.
 An important feature of the ROM BIOS is detecting new
hardware in the computer and reconfigure the operating system
as device driver.
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ROM Types
 PROM (Programmable Read Only Memory)
 Type of ROM that information is only installed once.
 The CD can be called PROM.
 EPROM (Erasable Programmable ROM):
 Type of ROM that can erase and rewrite it.
 "CD-Erasable" can be called EPROM.
 EEPROM (Electronic Erasable Programmable ROM):
 It form enhence of EPROM, a difference compared to the
EPROM is able to write and remove the information again
and again by software rather than hardware.
 Example: "CD-Rewritable".
 Application specific EEPROM is "flash BIOS". ROM is the
type of information can install or upgrade software.
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RAM – Random Access Memory
 Concept:
 RAM (Random Access Memory) to store in direct service
programs for the processing of the CPU.
 The RAM is only temporary data storage and data will be
deleted when power off.
 RAM operation
 Enter your information will be stored in RAM, then CPU will
retrieve data from RAM to handle.
 Types of RAM
 SRAM (Static RAM): SRAM is a type of RAM data storage
without the need to update regularly (static).
 DRAM (Dynamic RAM)
DRAM is a type of RAM should regularly update the data
(high refresh rate).
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SRAM – Static RAM
 Characteristics:
 Allow faster access than DRAM
 The memory chips are made of the transistors (switches) and
capacitors.
 Transistor SRAM can hold state power.
 SRAM is more expensive than DRAM
 Ex: L1, L2, L3 cache.
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DRAM - Dynamic RAM
 Characteristics:
 Dynamic RAM is mounted on the modules: DIMM , SIMM or
RIMM.
 Be plugged directly into the motherboard
 The most popular form factors:
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SIMM
DIMM
RIMM
SoDIMM
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SIMM - Single In-Line Memory Module
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DIMM - Dual Inline Memory Module
 DIMMs are 64-bit memory modules
 The DIMM RAM family: SDRAM, DDR, and DDR2.
 SDRAM: (Synchronous DRAM) With 84 pins per side, this
makes 168 independent pins on each standard .SDRAM
module and two keys notches.
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 DDR SDRAM (Double-Data Rate SDRAM)
memory has a total of 184 pins and a single
keying notch.
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 DDR2 has a total of 240 pins, one keying
notch, and an aluminum cover for both sides
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RIMM - Rambus DRAM
 A RIMM is a custom memory module that
varies in physical specification based on
whether it is a 16-bit or 32-bit module.
 The 16-bit modules have 184 pins and two
keying notches.
 The 32-bit modules have 232 pins and only
one keying notch.
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SoDIMM - Small Outline DIMM
 Memory in use for notebook and other
computers that require much smaller
components don’t use standard RAM
packages like the SIMM or the DIMM.
 Including: 144-pin EDO, 144-pin SDRAM and
200-pin DDR/DDR2.
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Structure Of Memory Chip
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RAS - Row Address Strobe
CAS - Column Address Strobe
Address Bus: signal address between RAS and CAS.
Data Bus is the data path between memory controller and
memory chips.
Column Address Decoder.
Row Address Decoder.
Row(column) addr latch.
Write Enable: check section to read - write the memory cell.
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The specifications of the RAM
 Bus speed: measured in MHz, is that the
volume of data in RAM can be transmitted to
the CPU once handled.
 Retrieve data speed: measured in billionths
of a second (nanosecond), the time interval
between two data acquisition of RAM
 Capacity: measured in MB (megabytes),
showing a maximum level of stocks of RAM
when the RAM data completely empty.
 RAM ECC (Error Correction Code): This is a
technique to test and debug in case of a bit
of memory was incorrect value data during
transport.
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Bandwidth of RAM
 Single Channel
 BandWidth = Bus Speed *8
 Ex: DDR-SDRAM 400 MHZ
• BandWidth = 400 *8 = 3200MB/s, is called PC3200.
 Dual Channel
 BandWidth = Bus Speed * 2*8 = Bus Speed * 16
 Ex: DDR 400 MHz => Bandwidth = 400*16 = 6400
 Is called 6400.
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