System RAM and Flash Memory
Where memory and RAM part ways
In our last section we discussed how memory is found in nearly every electronics device that works with data in one way or another. We've seen how electronic memory is different than storage found on discs: disc storage is cheaper and doesn't require constant power to retain information. Electronic memory on the other hand is much more expensive and usually requires a source of power to keep the information stored. The exception to electronic storage's requirement for a constant supply of power is in flash memory. Flash Memory is basically what you're buying when you buy SD memory cartridges or memory sticks for cameras and media players. When you purchase Flash Memory, what you are are buying is storage, like a hard disc for your mobile device. The drawback of Flash Memory being able to store data without a power source is speed.
An example of how a device works with memory is to use the home computer. A PC uses several types of memory in its system. Pocket PC's and media player's are basically miniature computers. If you're more interested in what kind of Flash Memory card you need for your digital camera or cell phone, check out Flash Memory. However, if you are interested in reading about the various roles of memory used in a PC, continue reading the next section.
The Many Roles of Memory on a Computer
- The first place that memory becomes apparent on your computer is when you first power it up. The first thing to wake up when a computer is powered on is a ROM (Read Only Memory) called the CMOS (Complementary Metal Oxide Semiconductor), pronounced See-Moss. CMOS is the name of the chip that stores software called BIOS (Basic Input/Output System), pronounced bye-ohs.
- BIOS performs POST (power on self test). This is how the computer checks to see that it has its vitals so it can be a computer. It would be like you waking up in the morning and before you get out of bed, ensuring you have the things required: Pulse? Check. Brain? Check. Feet? Check. Gotta pee? Check!
- The ROM is a form of Flash memory. It can retain the BIOS program without power. This is why it's the very first thing you get on a computer when it's powered on. The BIOS however is very slow compared to other forms of memory, but for its purpose it doesn't need a terrible amount of speed.
- The BIOS informs the system it has hard drives (disc storage) from which to read an operating system (OS). Disc storage is our second form of memory, but this is properly referred to as storage because it's non-electronic memory.
- While the OS loads our next form of memory is used, RAM. In modern computers you're probably using the latest RAM . SDR SDRAM or dual channel SDR SDRAM also called SDR2 SDRAM. These acronyms stand for Single Data Rate Synchronous Dynamic Random Access Memory, but it's just RAM. Basically, the letters that appear before RAM in the complete acronym just means very, very fast RAM.
- Since the computer is turned on there is power to all circuits. This means that system RAM can operate quickly and CPU, which is the fast, powerful brain, can utilize a pool of data that operates as quickly as it does. Modern RAM (SDR SDRAM) synchronizes with the CPU system clock allowing it to communicate with the CPU at an incredibly high rate of speed. In this capacity, memory is a temporary data storage area for the CPU. For example, it's like a mathematician doing complex equations with a chalk board. The chalk board is the memory the mathematician is the CPU.
Key terms in our discussion on the types and roles of memory include:
- Storage: Storage primarily reserved for hard drives, but as you've seen even hard drives are a form of RAM because data can be read from it from at random. But it isn't true memory. Most flash memory is actually storage for mobile devices.
- ROM: ROM is read only memory. Generally the ROM was a chip with a hard coded piece of software placed into it. It could never be erased or updated, hence "read only." However, with modern technology it's as easy to make flash memory as it is a true ROM, so most ROM today is really flash, so it can be rewritten or "flashed".
- CMOS: The CMOS holds a low level PC program called BIOS, which isn't erased when the computer is powered down. The BIOS gives the CMOS a simple job called POST. The BIOS can be revised to a new version depending on the needs of the manufacturer of your computer's mother board. This revision to the BIOS software in the CMOS is called a flash. This takes us full circle in our understanding of how flash memory works.
- RAM: Electronic memory that requires power at all times. It's very fast so it can help the CPU perform complex jobs much faster than Flash memory.
We could continue our focus on computer's system memory or system RAM and write volumes, but that's not our focus. Instead, we'll shift gears and delve deeper into flash memory and its many, in fact too many, varieties. The PC's use of its variety of memory was a good starting point to get familiar with the various types of memory.