MMC and SD
Because flash memory is available in such a wide variety of formats, it can be challenging to determine which of those formats is compatible with a given device. Flash memory can be used to increase the storage capacity of electronic devices such as MP3 players, personal digital assistants (PDAs), mobile phones, digital cameras, and personal computers; however, choosing the appropriate format for your device may be easier said than done.
Because it could be quite a lengthy read if we attempted to cover all of the common formats in a single Tech Tip, we have decided to break up our discussion of flash memory into two separate posts. The first part of this series on flash memory will concentrate on MMC and SD formats, which are very comparable to one another, widely used, and can often be interchanged with one another.
The Essence of It
Before getting into the specifics, it’s probably a good idea to go over some background information on each card. The term “MultiMedia Card” (also abbreviated as “MMC”) refers to a file format that was created in collaboration by SanDisk and Siemens in the year 1997. The letters “SD” stand for “Secure Digital,” and this format was jointly developed by SanDisk, Matsushita Electronics (also known as Panasonic), and Toshiba. This format is an improvement on the original design of MMC, and the letters “SD” stand for “Secure Digital.”
In both of these formats, the components are solid-state, meaning there are no moving parts, and they are protected from damage by a rigid plastic casing. The devices are generally unaffected by extreme temperatures, and they should be able to withstand a drop from a height of ten feet without incurring any damage from the shock.
Characteristics of the Body (MMC & SD)
Both MMC and SD flash memory units weigh only 2 grams and measure approximately 24 millimeters by 32 millimeters by 2.1 millimeters. This is comparable to the size of a standard postage stamp. The fact that they have such a small footprint makes it possible for the devices that can read them to be made more compact, but it also makes it easier for someone to lose their data. As consumer electronics continue to become more powerful, the devices themselves are getting smaller; consequently, the necessary accessories are needed to keep up. MMC and SD cards are physically distinguishable from one another due to the presence of a sliding tab and a different number of connections, despite the fact that they have the same basic form factor.
There will be a notch in the upper right corner of an MMC or SD card when you are looking at the card so that the label is facing you and the electrical connections are facing away from you. In this position, the label will be visible. From this vantage point, an SD card will have a small tab that can be slid along the left edge of the card, whereas an MMC card will not have this feature. If you look at the enlarged images very carefully and compare this 512MB MMC card to this 512MB SD card, you will be able to tell the difference between the two. This tab can be moved into two different positions, locked and unlocked, by sliding it. It gives the user the ability to manually write and protect the information that is stored on the card. This means that when the tab is in the locked position, information can be read from the card, but nothing can be written to or erased from the card.
The other noticeable physical distinction can be found on the card’s reverse side. While an SD card has nine electrical connections, an MMC card only has seven. These connections are small rectangular pads that allow for the transfer of data and the receipt of power.
To all intents and purposes, SD and MMC cards can be used interchangeably on modern devices. This is especially true if the device in question specifies that it is compatible with both types of memory cards (also known as “SD/MMC compatibility”).
The data transfer rates that can be accomplished by SD and MMC cards are nearly identical, with the SD cards having a very slight advantage. It is now possible to purchase SD cards with write speeds rated at 60x (9 MB/s) and read speeds rated at 66x (10 MB/s), whereas the transfer rates of MMC seem to reach their maximum capacity at 9 MB/s in either direction. There is not much of a difference between the two, and both are quite fast. However, results for end-users will vary, and it is possible that they will not reach these speeds in actual use, regardless of the format that is selected.
When you are out doing comparisons of different SD and MMC cards, speed should be listed as part of the technical specification, as this is an essential factor to take into account. There are still commercially available cards with slower transfer speeds, which can have a negative effect on the performance of digital cameras and other devices where speed may be an important factor. If the difference between 45x and 66x in the speed rating doesn’t seem like a big deal to you, perhaps thinking of it in terms of 6.75 MB/s versus 10 MB/s will change your mind. Each ‘x’ in the speed rating represents 0.15 MB/s. When referring to the faster cards, some manufacturers will use phrases such as “High Speed” or “Ultra” rather than providing actual speed ratings for the products.
Note: Before purchasing “Ultra” or “High Speed” chips, it is important to verify the actual write speed specifications of your device. It is possible that you will install a Hemi engine in an AMC Gremlin. If the camera does not support it, spending the extra money is not a good idea.
SD cards are readily available in capacities up to 1 gigabyte (GB), and models with a storage capacity of 2 GB are just beginning to become available. According to the SD Card Association, models with capacities up to 4 GB and 8 GB are also on the way. The most that can be stored on an MMC card is 512 megabytes, making the SD format a significantly more desirable storage medium.
As was discussed in the section that was devoted to the physical characteristics, SD cards come with the advantage of write protection. When a user “locks” their card, they can have the peace of mind of knowing that their data is protected until they take the necessary steps to unprotect it. If an SD card rather than an MMC card is used, there is less of a chance that the data will be altered or lost inadvertently, which significantly increases the data’s level of security.
Copyright protection is yet another function that is supported by SD, in contrast to MMC’s lack of support for this feature. This function is referred to as “cryptographic security for the protection of copyrighted data” on the SanDisk website, whereas in other places it is referred to as DRM, which stands for “digital rights management.” In general, licensed content can be written to an SD card, but it cannot be executed from anywhere other than the card itself.
In most cases, SD cards and MMC cards are compatible with one another, and either type can be used in a device that accepts them. In general, an SD card will cost more than an MMC card of the same capacity; however, as you can see from this Tech Tip, it does offer more in exchange for the additional cost.
Numerous card readers designed for personal computers offer the capacity to read from and write data to a wide variety of standard flash media formats. These readers can be found in abundance. Because two of the 15 different card formats, MMC and SD, can be read from the same slot on the device, a 15-in-1 reader/writer like this one can be made to be quite compact. This is one of the reasons why.
Users are able to increase the capacity of their MP3 players and the amount of time they can play their music if the device has an expansion slot. MP3 players typically come pre-loaded with a certain amount of memory that can be used to store music files. One example of such a device is the Pogo RipFlash MP3 Player, which has 256MB of memory already installed and an SD/MMC slot for simple expansion.
Because they have slots for flash memory, mobile phones and personal digital assistants (PDAs) can also take advantage of the increased storage space. The Handspring Treo 600 is a combination phone and personal digital assistant (PDA) that provides an SD card slot as well as an MMC slot for added convenience.
In addition, flash memory is used in digital cameras in place of film, so larger and faster memory cards are always appreciated as an upgrade option for these devices. Kodak DX7630 6.1MP 3x Optical Zoom 4x Digital Zoom Camera The 6.1 MegaPixel Kodak DX7630 could fill up the same SD/MMC card much faster than the 3.2 MegaPixel Umax AstraPix 640, but one of the great things about these cards is that the user can choose the size, as well as the quantity to have on hand, in order to suit their particular needs and budget. Another great thing about these cards is that they can be used in both digital and analog cameras.
A word of caution: make sure to check your device to see how much storage space it can handle on the card you’re using it. If your camera can only read cards up to 512 megabytes in size, then there is no point in using a card that is 1 gigabyte in size with it (depending on the device, some may not even be able to read the card at all, while others will only use the card up to the maximum capacity that it is rated for). In either case, you need to check to make sure that the card you use is compatible with the device. Always make sure to check the manual of the product you’re using to ensure that the memory you purchase is compatible with it.Advertisement