• Memòries SD (com triar-les quan tenen preus radicalment diferents donada una mateixa capacitat)

    Posted on March 24th, 2009 landreu No comments

    Desprès d’anys de comprar diferents tipus de memoria per als diferents dispositius que van passant per les meves butxaques, començant per la Compact Flash, passant per la “super-propietaria” MemoryStick de Sony i acabant per les SD, observo amb alegria que el mon i el mercat es va decidint per un únic model de memoria que pugui guardar les dades de diferents dispositius. I pel que veig aquest és el format SD. La porto a la càmera (Canon Powershot), la porto a la PDA (Palm Treo650) la poso al reproductor de música (no-Apple) l’endollo al PC-Desktop de casa i al portatil amb un adaptador USB.

    He considerat interessant enviar-vos uns “retalls” d’ informació sobre aquest tipus de memòria., que crec us ajudarà a entendre el seu preu segons model, el seu aspecte i a que no us donin “gat per llebre” a l’hora de decidir-vos a comprar-ne una, i poder comparar-les adeqüadament. Malgrat físicament totes “son iguals” internament no ho son, especialment quan a la seva velocitat d’escriptura i lectura.

    Per als que us

    Una mica d’historia:

    In August of 1999, Panasonic, SanDisk, and Toshiba first agreed to develop and market the SD (Secure Digital) Memory Card, which was a development of the MMC. With a physical profile of 24 mm × 32 mm × 2.1 mm, the new card provided both DRM up to the SDMI standard, and a high memory density for the time.

    The new format was designed to compete with Sony’s Memory Stick format that was released the previous year, which featured MagicGate DRM, and was physically larger. It was thought that DRM features would be widely used due to pressure from music and other media suppliers to prevent piracy. The features are largely unused.

    Sobre les Capacitats:

    Secure Digital (SD) is a flash (non-volatile) memory card format developed by Matsushita, SanDisk, and Toshiba for use in portable devices. Today it is widely used in digital cameras, handheld computers, PDAs, mobile phones, GPS receivers, and video game consoles. Standard SD card capacities range from 8 MB to 4 GB and for high capacity SDHC cards 4 GB to 32 GB as of 2008. Arribant a un límit teòric de 2TB en una pastilleta d’aquestes dimensions.

    Sobre les Velocitats:

    There are different speed grades available which are measured with the same system as CD-ROMs, in multiples of 150 kB/s (1x = 150 kB/s). Basic cards transfer data up to six times (6x) the data rate of the standard CD-ROM speed (900 kB/s vs. 150 kB/s). High-speed cards are made with higher data transfer rates like 66x (10 MB/s), and high-end cards have speeds of 200x or higher. Note that maximum read speed and maximum write speed may be different, with maximum write speed typically lower than maximum read speed. Some digital cameras require high-speed cards (write speed) to record video smoothly or capture multiple still photographs in rapid succession. The SD card specification 1.01 allows for a maximum speed of 66x. Higher speeds of up to 200x are defined by specification 2.0.

    The following table lists some common ratings and their respective maximum transfer rates.

    Rating

    Speed (MB/s)

    6x

    0.9

    32x

    4.8

    40x

    6.0

    66x

    10.0

    100x

    15.0

    133x

    20.0

    150x

    22.5

    200x

    30.0

    SDHC cards have SD Speed Class Ratings defined by the SD Association. The SD Speed Class Ratings specify the following minimum write speeds based on “the best fragmented state where no memory unit is occupied“:[19]

    · Class 2: 2 MB/s

    · Class 4: 4 MB/s

    · Class 6: 6 MB/s

    Si teniu curiositat per saber “com son per dins” penso que no cal que la “desmonteu” ni la feu malbé, algú ja ho ha fet per nosaltres…(aquesta pobre, té signes de violència a la carcassa…)

    En aquest cas podem veure un Xip de Samsung que és la memòria principal i una controladora d’accès a memòria que fou construïda la setmana 23 de l’any 2006 (ho encerclo en vermell). Si us hi fixeu la majoria dels Xips porten sempre la data de fabricació en un format de 4 dígits. És un “truqui” útil per quan us esteu esbarallant amb la placa d’audio d’un ordinador i no sabeu de quin any haurien d’ésser els drivers… Tots els elements son del tipus SMD (Surface Mounted Device) per tal de minimitzar-ne el gruix, I els pins o terminals queden protegits per la carcassa final plàstica, de possibles deposicions de greix, provocades pels dits dels usuaris poc curosos.

    Coses Noves que es fan amb aquest tipus de memòries:

    Eye-Fi, Inc. produces an SD card with Wi-Fi capability built in for 802.11g, 802.11b and backwards-compatible 802.11n wireless networks and supporting static WEP 40/104/128, WPA-PSK, WPA2-PSK security standards. The card works with any digital camera with an SD slot and can send captured images directly to a Windows PC or Apple computer wirelessly, where they can be automatically uploaded to web sites such as Flickr.com. When not in range of a wireless network connection, the card makes use of its 2GB capacity (EYE-FI-2GB model) until the images can be transferred.

    Coses “dolentes”, be l’unica cosa no òptima que hi trobo…

    Another limitation is that flash memory has a finite number of erase-write cycles. Most commercially available flash products are guaranteed to withstand around 100,000 write-erase-cycles.

    Dubto però que ningú hi faci tantes escriptures, doncs segur que amb el temps que trigueu a fer-les el producte ja s’haurà quedat totalment obsolet en quan a capacitat.

    Andreu Veà

    wiwiw.org

    PS: Part de la info d’aquest document l’he extret d’un molt complert article de la Wikipedia.