Flash Memory and Cache Memory Flash Memory

Standard RAM is volatile; when power to the PC is lost, all data currently stored in RAM is lost. This fact explains why you must save your work when using an application. One type of memory, called flash memory, stores data even when the power is turned off. ROM is a form of flash memory used in PCs. Other machines that use flash memory are digital cameras. When you take pictures with some digital cameras, the pictures are stored in a flash memory chip rather than on photo graphic film. Because you do not want to lose the pictures you have taken, the memory must store the pictures until you can transfer them to your PC, even when the camera is turned off.

Cache Memory

Moving data between RAM and the CPU's registers is one of the most time-consuming operations a CPU must perform, simply because RAM is much slower than the CPU. A partial solution to this problem is to include a cache memory in the CPU. Cache (pronounced cash) memory is similar to RAM, except that it is extremely fast compared to normal memory and it is used in a different way.

When a program is running and the CPU needs to read data or program instructions from RAM, the CPU checks first to see whether the data is in cache memory. If the data is not there, the CPU reads the data from RAM into its registers, but it also loads a copy of the data into cache memory. The next time the CPU needs that same data, it finds it in the cache memory and saves the time needed to load the data from RAM.

Since the late 1980s, cache memory has been built into most PC CPUs. This CPU-resident cache is often called Level-1 (L1) cache. The first CPU caches came with 0.5 KB, then 8 KB, then 16 KB, then 32 KB. Today Celeron processors have 128 – 256 KB built in.

In addition to the cache memory built into the CPU, cache is also added to the motherboard. This motherboard-resident cache is often called Level-2 (L2) cache. Many PCs sold today have 512 KB or 1024 KB of motherboard cache memory; higher-end systems can have from 2 MB to 4 MB of L2 cache.

Memory and Computing Power

The amount of RAM in a computer can have a profound effect on the computer's power. More RAM means the computer can use bigger, more powerful programs, and those programs can access bigger data files.

More RAM also can make the computer run faster. The computer does not necessarily have to load an entire program into memory to run it. However, the greater the amount of the program that fits into memory, the faster the program runs. For example, a PC with 16 MB of RAM is able to run Microsoft Windows 98, even though the program actually occupies about 195 MB of disk storage space. When you run Windows, the program does not need to load all its files into memory to run properly. It loads only the most essential parts into memory. When the computer needs access to other parts of the program on the disk, it can unload, or swap out, nonessential parts from RAM to the hard disk. Then the computer can load, or swap in, the program code or data it needs. While this is an effective method for managing a limited amount of memory, it can result in slow system performance because the CPU, memory, and disk are continuously occupied with the swapping process. If your PC has 64 MB of RAM (or more), you will notice a dramatic difference in how fast Microsoft Windows 98 runs because the CPU will need to swap program instructions between RAM and the hard disk much less often.

If you own a PC and decide that it needs more RAM, you should be able to buy more, open up your computer, and plug it in. (Some newer PCs come "stuffed" with all the RAM they can hold, making it difficult to upgrade.) In some computers, chips are usually grouped together on small circuit boards called single in-line memory modules (SIMMs) or dual in-line memory modules (DIMMs). Each SIMM or DIMM can hold between 1 MB and 64 MB of RAM and connects to the motherboard with 30-pin, 72-pin, or 168-pin connections. In newer computers both these modules are replaced by DDR и DDR II types that can hold up to 2 Gb of RAM.

The cost of upgrading the memory of a computer has actually gone down, so upgrading RAM is often the most cost-effective way to get more speed from your computer.