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Hope you are well in this rainy season. In this tech class, we will learn about memory cards/external storage cards as they are very important for any device in terms of its versatility for data storage.
What is Memory Card?
Memory cards can also be referred as flash drives, are small devices that are used to store electronic data. This can be anything, depending on the device from photos, music, movies, games, documents, programs and more. While cards come in a variety of shapes and sizes and are available for a variety of products, all memory cards do essentially the same thing, that is to store data.
Types of Memory Card:
Over the past few years, the number of different types of memory cards has reduced drastically, due to standardization. The main types currently available include SD, Memory Stick, and Compact Flash. Other, less common varieties in older devices include MMC, xD-Picture Card and SmartMedia.
Compact Flash (CF):
Invented by SanDisk Corporation in 1994, Compact Flash cards can support 3.3V and 5V operation and can switch between the two, in contrast to other small-form-factor flash memory cards that can operate only at one voltage. The card was designed based on the PCMCIA PC Card standard and can fit into a PCMCIA slot with an adapter. There are two types of CompactFlash cards to accommodate different capacities: Type I cards are 42.8mm x 36.4mm x 3.3 mm thick; Type II cards are 42.8mm x 36.4mm x 5.5 mm thick.
Secure Digital Card (SD card):
SD cards are used in many small portable devices such as digital video camcorders, digital cameras, handheld computers, audio players and mobile phones. Since 1999, SD Memory Cards are now available in capacities between 16 Megabytes and 128 Gigabyte and still growing. An SD card typically measures 32mm x 24mm x 2.1mm and weighs approximately 2 grams.
After the success of the SD Card (Secure Digital Card), the miniSD Memory Card was developed to meet the demands of the mobile phone market. The MiniSD Card provides the same benefits as the SD Card but is smaller than the original SD Card. MiniSD Cards are typically found in many newer mobile phones with features such as built-in digital cameras, downloading and games, basically, the mobile phones where the miniSD can meet the requirements for increased data storage. MiniSD cards are 21.5 mm x 20mm x 1.4 mm and generally provide 16MB to 1024 MB of storage.
Mainly used in mobile phones and other small handheld devices the MicroSD card is currently available in capacities up to 256 GB and still growing. It has roughly 1/4th the size of the SD card at 15mmx 11mmx0.7mm. The MicroSD card is also the smallest memory card available.
Multi Media Card (MMC):
The MultiMediaCard (MMC) standard was introduced by SanDisk and Siemens in 1997. The card itself is 32mm x 24 mm x 1.4mm and is often used in place of the SD card. Transfer speeds of an MMC are around 2.5MB/s and they can often be used in SD Card readers.
Sony Memory Sticks:
Sony Memory Sticks are light, compact and designed for a wide variety of devices including digital cameras, recorders, and more. With the use of an adapter, most Sony Memory Sticks can be used with almost all Memory Stick PRO-compatible products. The Memory Stick PRO format has an 8-bit parallel interface with theoretical transfer rates up to 480Mb/s. It is commonly used in high megapixel digital cameras and digital camcorders. The Memory Stick PRO Duo media is about one-third the volume and half the weight of standard-size media but offers all the advanced functions of Memory Stick PRO media.
Introduced by Toshiba in 1995 the Smart Media cards are now considered obsolete despite its popular usage for five years. SmartMedia cards are 45mm x 37mm x 0.76 mm and could be found in their peak times in 16MB, 32MB, and 128MB versions. Even as an obsolete card, it is still sought after by users of older devices which cannot use memory cards larger than 128MB.
Abbreviated as xD (Extreme Digital), the xD-Picture Card is a type of removable flash memory designed for use in digital cameras. The xD is ultra-compact with its size of 20mm x 25mm x 1.7mm. The xD-Picture Card was developed by Fujifilm and Olympus and are used in many models of digital cameras made by Olympus and Fujifilm.
How Memory Card Works:
Memory Card or Flash Card are made of transistors.The transistors in flash memory are like MOSFETs only they have two gates on top instead of one. This is what a flash transistor looks like inside. You can see it is a "n-p-n" sandwich with two gates on top, one called a control gate and one called a floating gate. The two gates are separated by oxide layers through which current cannot normally pass:
In this state, the transistor is switched off and effectively storing a zero. Both the source and the drain regions are rich in electrons (because they're made of n-type silicon), but electrons cannot flow from source to drain because of the electron deficient, the p-type material between them. But if we apply a positive voltage to the transistor's two contacts, called the bitline and the wordline, electrons get pulled in a rush from source to drain. A few also manage to wriggle through the oxide layer by a process called tunneling and get stuck on the floating gate.The presence of electrons on the floating gate is how a flash transistor stores a one. The electrons will stay there indefinitely, even when the positive voltages are removed and whether there is power supplied to the circuit or not. The electrons can be flushed out by putting a negative voltage on the wordline—which repels the electrons back the way they came, clearing the floating gate and making the transistor store a zero again.
Class of Memory Cards:
Memory Cards are now available in various class depending on their speed and capacity of video recording feature. The following table will explain in a short about this.
Memory cards are much more shockproof than other storage mediums. Since there are no moving parts in a memory card, they're much less prone to damage from movement, which can occur in a normal hard drive. They're also much less fragile than a CD/DVD.Since memory cards are physically so small, perhaps the greatest risk of data loss lies with losing the entire card itself, rather than by some other accident. Memory cards are quite sturdy and memory cards are capable of working through more than one million data write/read/erase cycles. Roughly it can be expected that a memory card to be capable of withstanding around 10,000 insertions. These numbers, of course, will differ slightly between manufacturers.
Credits: Google, Wikipedia,sdcard.org & other blogs.
Previous Tech Class Lessons
Chapter 1: Introduction to Smartphone Specifications
Chapter 3: All You Need To Know About Augmented Reality
Chapter 4: All You Need To Know About Charging Cycle
Chapter 5: All About Activity Tracker & Fitness Band
Chapter 6: Internet of Things & Mi Home
Chapter 7: Infrared Blaster
Chapter 8: CPU Architecture, CPU, GPU
Chapter 9: Megapixels and Photo Quality
Chapter 10: PDAF and its difference with CDAF
Chapter 11: All About Network Bands
Chapter 12: All About Rooting
Chapter 13: All about Kernel
Chapter 14: All you need to know about Wi-Fi!Chapter 15: All About CPU Cores
Chapter 16: All About TWRP
Chapter 17: All About RAM
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