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MEMORY CARDS

Mobile Sensei
Posts: 7,358

Intro to smartphone memory types/technologies

[ Edited ]
A short introduction to the different kinds of memory in a Symbian OS based smartphone (feel free to correct any mistakes or omissions, add clarifying details, etc.): Primarily the smartphone has two kinds of memory: volatile memory and non-volatile memory.

 

 

Message Edited by michaels on 27-Apr-2009 06:57 PM
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Mobile Sensei
Posts: 7,358

VOLATILE MEMORY

Volatile memory is memory which' contents are lost when the device is powered off. Mainly it comes in the form of RAM. RAM stands for Random Access Memory (meaning that each memory location has a direct and unique address that can be read or written to independently of any other location/address).

RAM is very fast to access, and it is used for primarily one thing: the run-time memory of software applications (including the device's operating system and any applications).

There is also a secondary use for RAM, where a part of it is allocated/reserved and used as if it was a storage drive. This is known as a RAM disk. On smartphones this is generally visible to some applications (such as file managers) as the D-drive. As it is volatile memory, only small temporary items/files should be stored there as its contents disappear when the device is powered off.
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Mobile Sensei
Posts: 7,358

NON-VOLATILE MEMORY

[ Edited ]
Non-volatile memory is memory which is retained even if the device is powered off. In other words, what's in non-volatile memory survives a device reboot.

This kind of memory can come in many "flavours" and it can be implemented using various different technologies.

For simplicity, I'll just call one "flavour" ROM (Read-Only Memory), and state that it is typically implemented using a memory technology called "Flash" (don't confuse it with Macromedia/Adobe Flash for web pages). Flash ROM on a phone contains the phone core software; the operating system and any additional supporting software. As it is read-only, it can't be written to by any applications. It can be only updated through the procedure known as "flashing" and usually it means you update the phone's firmware (which means the built-in phone software in ROM).

On smartphones some applications will see/show the ROM as the Z-drive. It can be viewed/read, but not written to. And on newer devices based on Symbian 9.1/S60 3rd Edition, access to specific directories (or "folders", if you prefer that term) is also protected from unprivileged applications.

(Note: There are also two different Flash ROM technologies in use these days; "NOR Flash" and "NAND Flash". A device can have one or the other, or both kinds. Without going into details, the main things to remember about these is that programs on NOR Flash can be run/executed without first loading the executable file to RAM. Programs on NAND Flash must first be loaded into RAM before it runs. NAND Flash is cheaper, but then requires the device to have more RAM to accomodate that.)

The second kind of non-volatile memory can be called "Flash RAM" as it is still based on the same Flash memory technology, but it is also writable (hence "RAM", as opposed to "ROM). This kind of memory is characterized as "user [storage] memory", or sometimes "phone memory". This is visible as the C-drive.

The C-drive is initialized with files/data that the operating system needs for various purposes (anything that needs a writable storage location that survives powering off the device). This is also the memory where by default things such as contacts, messages or photos are saved, when they are saved to "phone memory". Same goes for software applications (games or whatever) and their data files, when they are also installed to "phone memory".

Another writable storage solution that is also based on Flash memory technology, are the memory cards. The topic deserves its own "chapter"...


Message Edited by petrib on 12-Sep-2006
01:42 AM

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Mobile Sensei
Posts: 7,358

MEMORY CARDS

Memory cards are removable, writable storage usually also based on Flash memory.

(Note: Some devices, like the N91 - or at least it - do not have a removable memory card, but instead a very small magnetic disk drive, a microdrive.)

There are many different kinds of memory cards; different sizes and shapes. Keeping track of all the various different types is a bit of a pain, because there are some many. I try to cover the most relevant that I remember.

Originally Nokia devices used MMC (MultiMedia Card) type cards.

A related card type is the SD (Secure Digital) card. SD cards are physically very much like MMC cards (only slightly thicker and with some extra connectors/leads). However, they can be very different in function (they support additional security features, and can even be used for peripherals; so called, SDIO cards).

One additional thing to mention is that a device capable of handling (reading/writing) SD cards, can also handle MMC cards. The reverse is not true; a device that handles only MMC cards cannot take any SD cards (they shouldn't even fit, because they're thicker).

A "half-size" MMC card is known as RS-MMC (Reduced Size MMC). The first RS-MMC's and devices that supported them operated at a voltage range of approximately 3.3V (Volts). You could call these also high-voltage RS-MMC cards.

Later a version called DV RS-MMC, where DV stands for Dual-Voltage, was introduced. These also got a "marketing name" of MMCmobile for a higher-speed version by the organization that defines the card specifications. The DV cards operate at either approximately 1.8V or 3.3V. With these the key thing to remember is that a device that requires DV RS-MMC cards is not compatible with the "regular"/"original" RS-MMC cards that operate only at 3.3V.

A device that accepts full-size MMC cards will also handle RS-MMC type/size cards. Often RS-MMC are actually sold with an adapter that extent their size to be exactly that of full-size MMC.

(Note: Besides MMCmobile, there are also variations like MMCplus. There can also be MMC ROM memory cards, which cannot be written to.)

Getting back to the SD card type, and speaking of adapters... There is a variation of the SD card known as miniSD. As the name says, it is physically smaller (and available only in smaller capacities). A device that accepts SD cards, also accepts miniSD cards with an adapter that makes it fit a full-size SD card slot/reader.

There's also an even smaller card form-factor known as microSD (it used to be called TransFlash by its inventor company, SanDisk, but as the industry body in charge of SD card related standards/specifications adopted it, it was renamed to microSD to keep the "family name" consistent).

It probably is also worth noting that the SIM (Subscriber Identity Module) is a smartcard with processing power and storage capabity (contacts, messages, SIM application toolkit programs).

(Note: As it is not particularly relevant to Nokia's devices, I'll also ignore Flash memory cards like SmartMedia, Compact Flash or CF, and also the various different kinds of Sony MemoryStick cards; MemoryStick, MemoryStick Duo, MemoryStick PRO, etc.)
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Mobile Sensei
Posts: 7,358

SUMMARY

[ Edited ]
In summary, smartphones have:
  • RAM as the volatile run-time memory that do not survive cycling the device power
  • C-drive; a non-volatile (permanent), writable storage area (phone memory)
  • D-drive; a volatile temporary storage area reserved from RAM
  • E-drive; a non-volatile removable, writable (usually) memory card (which come in different types)
  • Z-drive; a non-volatile, non-writable storage area (where the firmware/operating system resides)

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    Message Edited by petrib on 12-Sep-2006
    01:37 AM

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    Mobile Sensei
    Posts: 7,358

    LINKS

    [ Edited ]
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