MEMORY TYPES

MEMORY TYPES

INTERNAL MEMORIES
n - CACHE MEMORY
n - RAM
n - ROM

EXTERNAL MEMORIES
n (AUXILARY MEMORY)
n - FLOPPY DISK DRIVE
n - HARD DISK DRIVE
n - CD-ROM
n (COMPACT DISC-READ ONLY MEMORY)

INTERNAL MEMORY
n RAM(READ ONLY MEMORY)
- SRAM(STATIC RAM)
- DRAM(DYNAMIC RAM)
-SDRAM
-SDR SDRAM
-DDR SDRAM
-DDR2 SDRAM
-RDRAM

n ROM (READ ONLY MEMORY)
-PROM(PROGRAMMABL E READ ONLY MEMORY)
- EPROM
-EEPROM
-FLASH MEMORY

CPU CACHE MEMORY
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are to cached memory locations, the average latency of memory accesses will be closer to the cache latency than to the latency of main memory.

Static random access memory
n Static Random Access Memory (SRAM) is a type of semiconductor memory. The word "static" indicates that the memory retains its contents as long as power remains applied, unlike dynamic RAM (DRAM) that needs to be periodically refreshed. (Nevertheless, SRAM should not be confused with read-only memory and flash memory, since it is volatile memory and preserves data only while power is continuously applied.) SRAM should not be confused with SDRAM, which stands for synchronous DRAM and is entirely different from SRAM, or with pseudostatic RAM (PSRAM), which is DRAM disguised as SRAM.
Dynamic random access memory
n Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor. As real-world capacitors are not ideal and hence leak electrons, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory. Its advantage over SRAM is its structural simplicity: only one transistor and a capacitor are required per bit, compared to six transistors in SRAM. This allows DRAM to reach very high density

DDR SDRAM
n gives a max transfer rate DDR memory (front and back shown) has 184 pins and one notchDDR SDRAM or double-data-rate synchronous dynamic random access memory is a type of memory integrated circuit used in computers. It achieves greater bandwidth than ordinary SDRAM by transferring data on both the rising and falling edges of the clock signal (double pumped). This effectively nearly doubles the transfer rate without increasing the frequency of the front side bus. Thus a 100 MHz DDR system has an effective clock rate of 200 MHz when compared to equivalent SDR SDRAM, the “SDR” being a retrospective designation.
n With data being transferred 8 bytes at a time DDR RAM gives a transfer rate of (memory bus clock rate) × 2 (for dual rate) × 8 (number of bytes transferred). Thus with a bus frequency of 100 MHz, DDR-SDRAM of 1600 MB/s.
n DDR-200: DDR-SDRAM memory chips specified to run at 100 MHz
n DDR-266: DDR-SDRAM memory chips specified to run at 133 MHz
n DDR-333: DDR-SDRAM memory chips specified to run at 166 MHz
n Chip specification
n DDR-400: DDR-SDRAM memory chips specified to run at 200 MHz

DDR2 SDRAM
n DDR2 SDRAM
n DDR2 SDRAM (Double Data Rate Two Synchronous Dynamic Random Access Memory) is a computer memory technology. It is a part of the SDRAM family of random access memory technologies, which is one of many DRAM implementations.
n Overview
n The advantage of DDR2 over DDR SDRAM is the ability for much higher clock speeds, due to design improvements. With a clock frequency of 100 MHz, "SDR-SDRAM" will transfer data on every rising edge of the clock pulse, thus achieving an effective 100 MHz data transfer rate. Unlike SDR, both DDR and DDR2 are double pumped; they transfer data on the rising and falling edge of the clock, at points of 0.0 V and 2.5 V (1.8 V for DDR2), achieving an effective rate of 200 MHz (and a theoretical bandwidth of 1.6 GB/s) with the same clock frequency. DDR2's clock frequency is further boosted by electrical interface improvements, on-die termination, prefetch buffers and off-chip drivers. However, latency is greatly increased as a trade-off. DDR2 Prefetch buffer is 4 bits wide, whereas DDR is 2 bits wide & DDR3 is 8 bits wide.
n Power savings are achieved primarily due to an improved manufacture process, resulting in a drop in operating voltage (1.8 V compared to DDR's 2.5 V). The lower memory clock frequency could also help — DDR2 can use a real clock frequency 1/2 that of SDRAM whilst maintaining the same bandwidth).
n DDR2-400: DDR-SDRAM memory chips specified to run at 100 MHz, I/O clock at 200 MHz
n Spec standards
n Chips
n DDR2-533: DDR-SDRAM memory chips specified to run at 133 MHz, I/O clock at 266 MHz
n DDR2-667: DDR-SDRAM memory chips specified to run at 166 MHz, I/O clock at 333 MHz
n DDR2-800: DDR-SDRAM memory chips specified to run at 200 MHz, I/O clock at 400 MHz

SDR SDRAM
n SDR memory (front only shown) has 168 pins and two notches.SDR SDRAM is Single Data Rate synchronous dynamic random access memory, a type of computer memory
n While other forms of DRAM have an asynchronous interface, meaning that it reacts immediately to changes in its control inputs, SDRAM has a synchronous interface
n SDRAM for PCs is rated for its potential maximum clock rate. Speeds included PC66, PC100, and PC133, representing 66, 100 and 133 megahertz. There were additional unofficial speeds for enthusiast SDRAM parts, such as PC150, for 150 MHz. SDRAM comes in 168-pin DIMMs for desktops, or 144-pin SODIMMs mainly used in laptops, while DDR SDRAM comes in 184-pin DIMMs, and DDR2 uses a 240-pin configuration.

RDRAM
n Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, created by the Rambus Corporation.
n FeatureS
n The Direct RDRAM features an architecture and a protocol designed to achieve high bandwidth.
n Although RDRAMs have a low pin count, a single device is capable of providing up to 1.6 GB/s bandwidth. Memory systems that use RIMMs (Rambus Inline Memory Modules), also
n RDRAM memory sticks are available in a number of different speeds. Quite fittingly, PC800 has an 800MHz data rate using a 400MHz clock rate, PC1066 has a 1066MHz data rate using a 533MHz clock rate, etc

Programmable read-only memory
n A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently. They are frequently seen in computer games, or such products as electronic dictionaries, where PROMs for different languages can be substituted.
n Programming
n A typical PROM comes with all bits reading as 1, burning a fuse during programming causes its bit to read as 0. The memory can be programmed just once after manufacturing by "blowing" the fuses (using a PROM blower),
The BIOS ROM
The main hardware component of the system BIOS is the system BIOS ROM itself. This is normally located in an electrically-erasable read-only memory (EEPROM) chip, which allows it to be updated through software control. This is commonly called a flash BIOS.

EEPROM
An EEPROM (also called an E2PROM) or Electrically-Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices (such as USB flash drives, in its flash memory version).

EPROM
n EPROM. The small window admits UV light during erasure.
n An EPROM, or erasable programmable read-only memory, is a type of computer memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in electronic circuits. Once programmed, an EPROM can be erased only by exposing it to strong ultraviolet light. EPROMs are easily recognisable by the transparent window in the top of the package, through which the silicon chip can be seen, and which admits UV light during erasing.

Flash memory
n A USB Flash Memory Device
n Overview
n Flash memory is non-volatile, which means that it does not need power to maintain the information stored in the chip. In addition, flash memory offers fast read access times (though not as fast as volatile DRAM memory used for main memory in PCs) and better shock resistance than hard disks. These characteristics explain the popularity of flash memory for applications such as storage on battery-powered devices.
n Flash memory is a form of EEPROM (Electrically-Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. In layman's terms, it is a form of rewritable memory chip that, unlike a Random Access Memory chip, holds its content without the need of a power supply. It is also an example of a Non-Volatile Read Write Memory (NVRWM). The memory is commonly used in memory cards, USB flash drives, MP3 players, digital cameras and mobile phones.