Flash memory
Flash memory has become hugely popular in todays world of modern gadgets by providing a cost effective way of storing data. Example applications include PDAs (personal digital assistants), laptop computers, mp3 players, digital cameras and mobile phones. Flash memory is extremely durable, portable and can withstand temperature extremes.
Examples of Flash Memory:
Compact Flash: This type of memory is most often used in the digital cameras. They have a small controller chip, and they are thicker than the smart media flash memory. The circuit board will have the flash memory chips with the controller chip controlling all the operations. The general length and width of any compact flash card would be 36mm and 43mm respectively. There are two types of cards being Type 1 and Type 2. The thickness of the Type 1 card would be 3.3 mm and the Type 2 will have a thickness of 5.5mm. Many device makers are moving towards the SDHC type of card. Adapters are also available to go from CF to SD.
Secure Digital Card (SD): These are extensible cards, which may have a varying storage capacity generally up to 4gb. They are mainly used for portable digital devices. SD cards have varying speed ratings ranging from 66x to 133x commonly labelled as 'High Speed' and 'Ultra High Speed' at 150x. Note: speed ratings changed with the later version of the SD card below, and more on transfer speeds can be found further down the article.
Secure Digital Card High Capacity (SDHC): SDHC cards come in three formats being SDHC, miniSDHC and microSDHC. These are the latest versions of the SD card range and most new devices as of around 2007 will make use of SDHC card variants. They range in capacity size from 4GB to 32GB. Transfer speeds are denoted in classes being Class 2: 2 MB/s; Class 4: 4 MB/s and the fastest being Class 6: 6 MB/s. Note: SDHC cards may not be compatible with devices that used the older SD card, check with device manufacturer.
Memory Stick: The Sony Memory Stick is Sony's own version of flash memory for it's devices including cameras, mobile phones etc.. The Memory Stick Pro "High Speed" card features transfer speeds to 80 MB/s and comes in 256MB through to 8GB capacities. The much smaller Memory Stick DUO card is commonly used in their phones and compact cameras although there are adpaters available to fit Memory Stick Pro devices. There is also the new Memory Stick Micro (M2) especially for mobile phones with capacities ranging from 1GB to 8GB
PCMCIA:PCMCIA ATA Flash Cards can perform the role of a normal disk drive with far less power consumption and increased durability.
Smart Media: They are also used in digital cameras. The dimension would be 37mm width and 45mm length. The thickness is almost less than 1mm making it thinner than a compact flash card. These type of cards have not been in popular use for some years.
Memory cards for video game consoles: Flash memory is also popular in the game consoles, where it is often used instead of EEPROMs or battery-powered SRAM for game save data.
Technical Overview of Flash Memory
Flash memory is similar to EEPROM technology. It is a non-volatile computer memory which can be reprogrammed over an over. Their primary purpose or use lies in the memory cards and USB flash drives. They can be used similar to other hard disks either for general storage or for transfer of data between computer and digital components. The advancement in flash technology has enabled us to erase only a part of the memory and then reprogram the erased part rather than erasing the memory completely and then reprogramming from the scratch. One of the main advantages of the flash memory is that they are available at a cheaper cost than the EEPROMs and hence they have dominant value in today's memory market.
Modules of Flash Memory Rather than using single chip, one could use sufficient number of chips depending on the data to be stored and processed. The collection of chips together is called modules. Modules could be of two types:
Flash Cards: This would be the simplest way to construct modules using the flash memory. The flash chips are mounted onto a small card. This small card would act as the flash card. It will possess a standard interface and therefore they can very well interface with any number of products. They could be very conveniently plugged into any sort of digital device. For e.g., a minute of music could be stored in a 1Mbyte memory, to play an hour of music you may need 64MB.
Flash Drives: These are solid-state electronic devices. They are specially designed to replace the hard disk at certain places where durability and portability is of critical importance. They can totally replace the hard disks. The access time and seek time is shorter and they are much faster.
Transfer rates: The speed of reading or writing is generally stated as MB/s. Sometimes they may also be specified as 100x/150x. This 1x denotes 150kbps (Kilobytes per second), so, a 100x card roughly equals a transfer speed close to 15mbps (15,000kbps). An example of where transfer speed comes into play would be the digital camera, when shooting images in rapid succession, if the transfer speed is too slow the camera will pause shooting until writing to the memory card is done. Also to note with flash memory is that erasing and writing speeds can slow down with age.
Capacity: Flash memory is available in a wide, and ever increasing, array of capactity sizes. The storage capacity increase follows the Moore's law, as they are developed by constructing the integrated circuits together. Some of the common flash memory capacities would be 512MB through to 8GB and extremely large versions at 64GB. Choosing the capacity of the flash memory depends on the application or the digital device in which you may install the flash memory. For example a high end digital camera will be wanting to store images of around 4-5mb in file size, so, to shoot around 200 images will need at least a 1gb card.
Camera megapixel rating x Memory Card capacity x No. of Photos
| Camera Megapixels | File size | 128mb card | 256mb card | 512mb card | 1gb card | 2gb card | 4gb card | 8gb card |
|---|---|---|---|---|---|---|---|---|
| 5 | 2.5mb | 51 | 102 | 205 | 410 | 819 | 1638 | 3277 |
| 6 | 3mb | 43 | 85 | 171 | 341 | 683 | 1365 | 2731 |
| 7 | 3.5mb | 37 | 73 | 146 | 293 | 585 | 1170 | 2341 |
| 8 | 4mb | 32 | 64 | 128 | 256 | 512 | 1024 | 2048 |
| 9 | 4.5mb | 28 | 57 | 114 | 228 | 455 | 910 | 1820 |
| 10 | 5mb | 26 | 51 | 102 | 205 | 410 | 819 | 1638 |