Reconnect Internet Technology Tips

Flash memory gets its name due to its microchip arrangement in such a way, that its section of memory cells gets erased in a single action or “Flash”.
Both NOR and NAND Flash memory were invented by Dr. Fujio Masuoka from Toshiba in 1984.The name ‘Flash’ was suggested because the erasure process of the memory contents reminds a flash of a camera, and it’s name was coined to express how much faster it could be erased “in a flash”. Dr. Masuoka presented the invention at the International Electron Devices Meeting (IEDM) held in San Jose, California in 1984 and Intel recognizes the potentiality of the invention and introduced the first commercial NOR type flash chip in 1988, with long erase and write times.

Flash memory is a form of non-volatile memory that can be electrically erased and rewrite, which means that it does not need power to maintain the data stored in the chip. In addition, flash memory offers fast read access times and better shock resistance than hard disks. These characteristics explain the popularity of flash memory for applications such as storage on battery-powered devices.

Flash memory is advance from of EEPROM (Electrically-Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. Unlike an EPROM (Electrically Programmable Read-Only Memory) an EEPROM can be programmed and erased multiple times electrically. Normal EEPROM only allows one location at a time to be erased or written, meaning that flash can operate at higher effective speeds when the systems using; it read and write to different locations at the same time.

Referring to the type of logic gate used in each storage cell, Flash memory is built in two varieties and named as, NOR flash and NAND flash.
Flash memory stores one bit of information in an array of transistors, called “cells”, however recent flash memory devices referred as multi-level cell devices, can store more than 1 bit per cell depending on amount of electrons placed on the Floating Gate of a cell. NOR flash cell looks similar to semiconductor device like transistors, but it has two gates. First one is the control gate (CG) and the second one is a floating gate (FG) that is shield or insulated all around by an oxide layer. Because the FG is secluded by its shield oxide layer, electrons placed on it get trapped and data is stored within. On the other hand NAND Flash uses tunnel injection for writing and tunnel release for erasing.

NOR flash that was developed by Intel in 1988 with unique feature of long erase and write times and its endurance of erase cycles ranges from 10,000 to 100,000 makes it suitable for storage of program code that needs to be infrequently updated, like in digital camera and PDAs. Though, later cards demand moved towards the cheaper NAND flash; NOR-based flash is hitherto the source of all the removable media.

Followed in 1989 Samsung and Toshiba form NAND flash with higher density, lower cost per bit then NOR Flash with faster erase and write times, but it only allows sequence data access, not random like NOR Flash, which makes NAND Flash suitable for mass storage device such as memory cards. SmartMedia was first NAND-based removable media and numerous others are behind like MMC, Secure Digital, xD-Picture Cards and Memory Stick. Flash memory is frequently used to hold control code such as the basic input/output system (BIOS) in a computer. When BIOS needs to be changed (rewritten), the flash memory can be written to in block rather than byte sizes, making it simple to update.
On the other hand, flash memory is not practical to random access memory (RAM) as RAM needs to be addressable at the byte (not the block) level. Thus, it is used more as a hard drive than as a RAM. Because of this particular uniqueness, it is utilized with specifically-designed file systems which extend writes over the media and deal with the long erase times of NOR flash blocks. JFFS was the first file systems, outdated by JFFS2. Then YAFFS was released in 2003, dealing specifically with NAND flash, and JFFS2 was updated to support NAND flash too. Still, in practice most follows old FAT file system for compatibility purposes.
Read More

CCNA and CCNP candidates who have their own Cisco home labs often email me about an odd situation that occurs when they erase a switch’s configuration. Their startup configuration is gone, as they expect, but the VLAN and VTP information is still there!

Sounds strange, doesn’t it? Let’s look at an example. On SW1, we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:

SW1#show vlan br

10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

We want to totally erase the router’s startup configuration, so we use the write erase command, confirm it, and reload without saving the running config:

SW1#write erase

Erasing the nvram filesystem will remove all configuration files! Continue?

[confirm]

[OK]

Erase of nvram: complete

00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram

SW1#reload

System configuration has been modified. Save? [yes/no]: n

Proceed with reload? [confirm]

The router reloads, and after exiting setup mode, we run show vlan brief again. And even though the startup configuration was erased, the vlans are still there!

Switch#show vlan br

10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active
Read More

Statistics show that the first three hours after a child’s abduction are most critical to recovery efforts. By combining the efforts of the wireless industry with the U.S. Department of Justice, the National Center for Missing & Exploited Children® (NCMEC) and law enforcement agencies, the Wireless AMBER Alerts™ initiative will be a catalyst for the more than 200 million wireless subscribers to aid in the search for and recovery of an abducted child.

AMBER

According to NCMEC, more than 260 children have been recovered since the AMBER Alert program began in 1997. The program-an early warning system to find abducted children-started as a local effort in the Dallas-Fort Worth, Texas, area and became a national initiative in 2003. AMBER stands for “America’s Missing: Broadcast Emergency Response.” The program is a legacy to Amber Hagerman, a 9-year-old girl who was kidnapped while riding her bicycle in Arlington, Texas, and was later found murdered.

An estimated 70 percent of Americans have wireless phones, and together they can serve as a national network that assists families and the authorities in searching for abducted children. By signing up to receive Wireless AMBER Alerts, subscribers receive information about local Alerts, as well as updates as the search progresses.
Read More