Access speed. Read/writes per second. Memory is, as with all technology, in constant metamorphosis. You have DRam, SDram, DDR, DDR2, DDR3, and several others. Its all about what mhz they operate at. The higher the frequency, the faster the access. The newer stuff is not only faster, but uses less energy and has higher capacity due to increasingly efficient nano-technology (ie: the size and spacing of the circuit paths).
If we were to use a physical media such as a hdd for main memory, even with today's uber-fast sata drives, you'd be surprised at how much slower it would run. Thank the techno-gurus that we're long past having to pull out a half dozen 5.25 floppies just to get our computer booted up and load a program or two, all on a monochrome/green monitor, with a whopping 16k of slug memory!
DRAM
The two major categories of RAM are dynamic RAM (DRAM) and static RAM (SRAM). DRAM is cheaper and used for main memory in computers, while SRAM is faster but more expensive and is used in caches or for smaller, high-speed memory.
Cache memory is special, high-speed static memory that is used to reduce the amount of accesses to dynamic RAM. While cache memory used to be on the motherboard, it is now most commonly found inside the CPU. Static memory is larger, costlier to produce, and uses more current than DRAM. But static memory is the fastest type of memory there is and it doesn't need refreshed (so long as the power is maintained). So cache is a compromise to store the most used code and data to reduce the access to the slower DRAM.
Conventional DRAM, of the type that has been used in PCs since the original IBM PC days, is said to be asynchronous. This refers to the fact that the memory is not synchronized to the system clock. A memory access is begun, and a certain period of time later the memory value appears on the bus. The signals are not coordinated with the system clock at all, as described in the section discussing memory access. Asynchronous memory works fine in lower-speed memory bus systems but is not nearly as suitable for use in high-speed (>66 MHz) memory systems. A newer type of DRAM, called "synchronous DRAM" or "SDRAM", is synchronized to the system clock; all signals are tied to the clock so timing is much tighter and better controlled. This type of memory is much faster than asynchronous DRAM and can be used to improve the performance of the system. It is more suitable to the higher-speed memory systems of the newest PCs.
gram (most commonly kilogram) slug dram
both are semiconductor memory. semiconductor means that both need continuous voltage or charge to sustain their data. SRAM used for cache , and store data in the flip flop, no need for refreshing , fast access but more expensive. DRAM used for main memory , and store data in capacitor, need for refreshing , slow access but less expensive.
In the most common form of computer memory, dynamic random access memory (DRAM).
Various versions of dynamic random access memory called DRAM.
Short for static random access memory, and pronounced ess-ram. SRAM is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that it doesn't need to be refreshed like dynamic RAM. To store 1 bit of information about 6 transistors are used and it does not required refreshing. Because Six transistors are used to store 1 bit of information, it is more costlier than DRAM in terms of cost per bit, where only 1 transistor and 1 capacitor is used to store 1 bit of information.DRAM stands for dynamic random access memory, a type of memory used in most personal computers. In DRAM to store 1 bit of information 1 transistor and 1 capacitor is used. The information is stored in the capacitor in form of charge, so it required refreshing to retain the charge or data in the capacitor.SRAM is Static RAM and DRAM is Dynamic RAM. DRAM is slower than SRAM and needs to be refreshed where SRAM does not and is used for cache.(Static RAM) SRAM is similar to DRAM but does not constantly refresh. SRAM is faster and more expensive than DRAM and is generally used for speed-critical areas of the computer such as cache memory.(Dynamic Random Access Memory) DRAM is the most common type of memory and is "dynamic" because in order for the memory chip to retain data, it must be refreshed constantly (every few milliseconds). If the cell is not refreshed, the data is lost. DRAM temporarily stores data in a cell composed of a capacitor and a transistor. Each cell contains a specified number of bits. These cells are accessed by row addresses and column addresses.
The computer's main memory is called Random Access memory(RAM). RAM is where the currently running programs reside.However, let's clear up one thing. There is an even faster type of RAM which is in the CPU itself, and that is cache memory. While modern dynamic RAM (DRAM) is fast, it still isn't as fast as the fastest static RAM. DRAM constantly has to be refreshed, while SRAM doesn't. However, SRAM is more expensive and uses more power. So as a compromise, there are special high-speed memory areas known as cache memory that stores the most used instructions and data as to reduce the amount of system RAM access. Since it is inside the CPU and is static memory, it is quite faster than the system DRAM memory.So while the system DRAM memory contains all the operating programs, the SRAM caches in the CPU contains things that are more immediate or are used more often.
SRAM is static RAM. It does not need to be refreshed like DRAM. Although it is faster than DRAM it is also very expensive. So it is not used computer prices would triple. Don't get that confused with SDRAM...that's a whole different story.
One dram is equal to about 1/8 of an ounce or approximately 3.7 milliliters. It is commonly used as a unit of measurement for liquid medications or essential oils.