Understanding RAM: Types and Uses
What is RAM (Random Access Memory)?
RAM (Random Access Memory) is a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.
Two Basic Types of RAM
There are two main types of RAM:
- DRAM (Dynamic RAM): Needs to be refreshed thousands of times per second.
- SRAM (Static RAM): Does not need to be refreshed as often, making it faster but also more expensive than DRAM.
Both DRAM and SRAM are volatile, meaning they lose their content when the power is turned off.
Types of RAM
VRAM (Video RAM)
VRAM (Video RAM) is a special-purpose memory used by video adapters. Unlike conventional RAM, VRAM can be accessed by two different devices simultaneously. This allows a monitor to access the VRAM for screen updates while a graphics processor provides new data. VRAM yields better graphics performance but is more expensive than standard RAM.
SIMM (Single In-line Memory Module)
SIMM (Single In-line Memory Module) is a type of memory module consisting of a small printed circuit board that holds memory chips. SIMMs are inserted into SIMM sockets on the motherboard or memory board. They are easier to install than older individual memory chips and are measured in bytes instead of bits.
DIMM (Dual In-line Memory Module)
DIMM (Dual In-line Memory Module) is another type of memory module. It consists of a small printed circuit board holding memory chips and is inserted into a DIMM socket on the motherboard. DIMMs generally use a 168-pin connector.
DIP (Dual In-line Package)
DIP (Dual In-line Package) is a packaging type for memory chips. It consists of a rectangular housing with two rows of connecting pins on each side.
RAM Disk
A RAM Disk refers to RAM that has been configured to simulate a hard disk. Files on a RAM disk can be accessed in the same way as those on a hard disk, but a RAM disk is approximately a thousand times faster. RAM disks are particularly useful for applications that require frequent disk accesses.
Note: Because RAM disks are made of volatile RAM, they lose their contents once the computer is turned off. To use a RAM disk, you need to copy files from a physical hard drive at the beginning of the session and copy them back before shutting down. Data on the RAM disk will be lost in the event of a power failure. The DOS operating system can convert extended memory into a RAM disk using the vdisk command (short for virtual disk), which is another name for RAM disks.
Cache or RAM Cache
A cache is a special high-speed storage mechanism. It can be either a reserved area of main memory or an independent high-speed storage device. Two types of caching are frequently used in personal computers:
- Memory Caching: Sometimes called cache storage or RAM cache, is a portion of high-speed static RAM (SRAM).
- Disk Caching.
Memory caching uses high speed SRAM and is more effective than the slower and cheaper dynamic RAM (DRAM) used as main memory.
Caching is effective because programs often access the same data or instructions repeatedly. By keeping this information in SRAM, the computer avoids accessing the slower DRAM. When data is found in the cache, it’s called a “hit.” Cache systems are judged by their “hit rate.”
Cache systems use “smart caching” technology, which allows the system to recognize certain types of frequently used data. Strategies for identifying which information should be placed in the cache are among the most interesting problems in computer science. Some caches are built into the architecture of microprocessors. For example, the Pentium II processor has a 512 KB L2 cache.
SRAM (Static Random Access Memory)
SRAM (Static Random Access Memory) is a type of memory that is faster and more reliable than the more common DRAM (Dynamic RAM). The term “static” indicates that it needs to be refreshed less often than dynamic RAM. SRAM chips have access times of around 10 to 30 nanoseconds, while DRAM is above 30 nanoseconds. Bipolar and ECL memories have even faster access times, below 10 nanoseconds.