Trabajo Memorias flash

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1 Memorias flash II-PEI 09/10 Trabajo Memorias flash Wojciech Ochalek This document explains the concept of flash memory and describes it s the most popular use. Moreover describes also Microdrive s technology. Finally contains comparison between this two technologies. 1. INTRODUCION The point of this work is to explain the term of flash memory - what is a flash memory? How it is built? How it works? What is it s use? What are advantages and disadvantages of use this kind of memory? Why it is so popular in portable devices? Moreover it is worth to know what is a USB flash drive and why it is the most popular use of flash memory? We also can not forget about Microdrives technology. How it differs from flash memory? Which of this technologies are better? Answers to all these questions can be found below. 2. FLASH MEMORY 2.1. The beginnings of flash memory Flash memory was invented by dr. Fujio Masuoka in Next in 1988 Intel develops first commercial version of NOR-type flash memory - it had 256 kilobytes of memory and size of shoe s box. One year later Samsung and Toshiba realised another type of memory flash - NAND Definition Flash Memory is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory). Difference between normal EEPROM and flash memory is that normal EEPROM erases it s content one byte at a time. This makes it slow to update. Flash memory can erase it s data in entire blocks, making it a preferable technology for applications that require frequent updating of large amounts of data as in the case of a memory stick. Furthermore flash memory costs far less then normal EEPROM. Flash memory is a non-volatile computer storage, that s mean that no power is needed to maintain the information stored in the chip. What s more flash memory offers us fast read access time and better kinetic shock resistance than hard disks. These characteristics explain the popularity of flash memory in portable devices Uses Flash memory is a technology that is primarily used in memory cards and USB flash drives. In all of the following devices is used flash memory: PADs (personal digital assistants), BIOS chip, laptop computers, digital audio players, digital cameras, mobile phones, console video game and many others.

2 2.4. How works? Flash memory has a grid of columns and rows with a cell that has two transistors at each intersection. One cell has two transistors, one of the transistors is known as a floating gate, and the other one is the control gate. This two transistors are separated from each other by a thin oxide layer. On the floating gate electrons are accumulated. Cell voltage is controlled by the amount of this electrons, which act as a barrier between the control gate and the floating gate. The floating gate's only link to the wordline through the control gate. As long as this link is in place, the cell has a value of 1. A special device called a cell sensor monitors the level of the charge passing through the floating gate. If the flow through the gate is above the 50% it has a value of 1. When the charge passing through drops below the 50% threshold, the value changes to Types of flash memory There are to types of Flash Memory - NOR-type and NAND-type. The name depends on the structure of the interconnections between memory cells.

3 In NOR gate flash, each cell has one end connected directly to ground, and the other end connected directly to a bit line. This type of memory give us long time to save and erase data but thanks to direct access to each memory cell, it s ideal for storing firmware. This memory can survive from to cycles of erasing. In NAND gate flash, only one cell has connected directly to ground, and one cell connected directly to a bit line. This type of memory is faster and cheaper then NORtype. Has the same size with more capacity and can survive 10 times more cycles of erasing then NOR. In NAND-type memory we have sequential access to data, which may be used as mass storage, useless as a main memory. In 2003 was invented new technology calls MLC (Multi Level Cell). Advantages of this technology is that we can save 2 bits of information in every cell. This make flash memory cheaper and smaller size at the same capacity. Then in 2006 appeared next technology calls X4. This technology give us possibility to save 4 bits of information in every cell. And because of that technology is 30% cheaper then MLC Memory cards One of the most important use of flash memory are memory cards. There are a lot of types of memory cards e.g.: SD (Secure Digital), Memory Stick, XD (Picture Card), Compact Flash, Multi Media Card. The most important and the most popular of this cards are SD and Compact Flash. Advantages of SD are fact that it has protection against illegal copying and also some switch witch protect our data from accidental erasure. Capacity of this cards is between 8 and 64 GB. Other standards of the SD are minisd and microsd. MicroSD is the smallest mass-produced memory card. All of memory cards are use in digital cameras, digital camcorders, media players and mobile phones and many others portable devices. Small size and weight, no need of power to maintain a information, high reliability, high resistance to damage and very good transfer rates all of this things makes flash memory so popular in portable devices.

4 2.7. USB Flash Drives USB Flash Drive is the most common use of flash memory. 1 - USB connector 2 - USB mass storage controller device 3 - Test points 4 - Flash memory chip 5 - Crystal oscillator 6 - LED 7 - Write-protect switch (Optional) 8 - Space for second flash memory chip Uses of pendrives: - personal data transport: we use they mainly to transport and store our data such a documents, pictures and videos. - system administration: they are particularly popular among system and network administrators, who load them with configuration information and software used for system maintenance, troubleshooting, and recovery. they are also use as a means to transfer recovery and antivirus software to infected PCs. - Application carriers: to carry applications that run on the host computer without requiring installation. - booting operating systems: most current PC firmware permits booting from a USB drive, allowing the launch of an operating system from a bootable flash drive. Such a configuration is known as a Live USB. - audio players: many companies make small solid-state digital audio players, essentially producing flash drives with sound output and a simple user interface e.g. ipod Shuffle. Some of these players are true USB flash drives as well as music players; others do not support general-purpose data storage. - backup: a flash drives can be used as backup medium for example in some company it could be use to save a database backup on every ends of day. Alternatively, the drive can be left inserted through the day, and data regularly updated. 2.8.Advantages and disadvantages of USB flash Drives Data stored on flash drives are impervious to scratches and dust, and flash drives are mechanically very robust making them suitable for transporting data from place to place. Compared to hard drives, flash drives use little power, have no fragile moving parts, and are small and light. Flash drives implement the USB mass storage device class so that most modern operating systems can read and write to them without installing device drivers. Some flash drives retain their memory even after being submerged in water, even through a wash machine. Like all flash memory devices, flash drives have a limited number of write and erase cycles before failure. Most USB flash drives do not include a write-protect mechanism. A drawback to the small size is that they are easily misplaced, left behind, or otherwise lost. Compared to other portable storage devices, for example external hard drives, USB flash drives have a high price per unit of storage.

5 3. TECHNOLOGY OF MICRODRIVES The Microdrive is a brand name for a miniature, 1-inch hard disk designed to fit in a CompactFlash (CF) Type II slot. In contrast to the flash memory it is the only storage memory for portable devices which works in mechanical way. It is made in the same way as traditional hard disks. Advantages of microdrives are that they allow more write cycles then flash memory, making them suitable for use as swapspace in embedded applications. Moreover Microdrives might be better at handling power loss in the middle of writing. Flash storage always needs to move some old data around while writing, to ensure the flash's finite write life is consumed equally; if there were a bug in the wear levelling algorithm it could cause data loss if the card were unplugged at the exact wrong time. Data on a magnetic hard drive is modified in place, and hard drive algorithms have many years more experience and testing over Flash. There are also some disadvantages. Due to being mechanical devices they are more sensitive to physical shock and temperature changes than flash memory. Microdrive s collapse the table to the floor, or knock on a hard object can damage the sectors. Microdrives also needs more power then flash memory, especially when disc starts and furthermore unlike flash memory, Microdrives require power even when no data is being transferred to them to keep the disc spinning. Microdrives are not as fast as the high-end CompactFlash cards (Microdrives 4-6 MB/s,CompactFlash 45 MB/s) and less capacity than CompactFlash cards and USB flash drives. Devices with Microdrives: Apple ipod mini, Creative MuVo, Creative ZEN Micro, Nokia N91, palmone LifeDrive, iriver H CONCLUSION Small size and weight, no need of power to maintain a information, high reliability, high resistance to damage and very good transfer rates all this facts make flash memory ideal to use in portable devices. One big disadvantage is that flash memory have limited cycles of erasing before failure. Despite of this it is widely used in many fields, mainly in memory cards and pendrives. This technology is used in many devices like PADs, BIOS chips, laptop computers, digital audio players, digital cameras, digital camcorders, mobile phones, console video game and many others. There is also another technology which can compete with flash memory. It s Michrodrives. It is the only storage memory for portable devices which works in mechanical way. Fact that Mirodrives have some moving parts makes it more sensitive for damage (physical shock and temperature changes). Moreover Microdrives need more power, have less capacity, and are slower then flash memory. The big advantage of Microdrives is that they allow us for more erasing cycles. BIBLIOGRAPHY: 1) 2) 3) 4) 5)