RAM holds temporary instructions and data needed to complete a task!
RAM consists of chips of memory, either in short chips (Dual In-line Pin (DIP) chips) or in memory modules called "Single Inline Memory Module" SIMMs, "Single Inline Pin Packets" SIPPs, DIMMs (Dual In-Line Memory Modules, etc.
A SIMM will have a number (most often 8 or 9) of Dynamic RAM (DRAM) chips mounted on it. The DRAM chips are the actual memory, and the SIMM chips hold the DRAM and interface it to the system bus.
This illustration is Courtesy of Kingston Technology Corp.
and shows two SIMM chips (9 DRAM chips per SIMM chip, so it is parity memory)
in a memory bank; and just in front of the SIMM chips, there is some external "cache" memory chips
(in DIPs) mounted directly to the board.
DRAM chips are mounted on SIMM chips like this:
SIMMs and SIPPs come in various pin configurations, SIMMs originally were 30 pin boards, and later 72 pin chips (boards), etc. DIMMs can come in 168 pin boards, allowing for 64 bit storage. DIMMs must have special motherboard receptacles, but DIMM is high capacity modules. In actuality, SIPPs are old technology, so you may never see a SIPP chip.
Each 30-pin SIMM chip can contain from 256KB to 4 MB memory, and 72 pin SIMMs can have from 1 MB to 32 MB memory (see table below).
Courtesy of Kingston Technology Corporation.
Memory chips (whether SIMMs or SIPPs) are placed in receptacles which are usually arranged in banks of 4 or 8 receptacles (see the first illustration above).
RAM is normally divided (or used by the PC) into three primary areas:
When you boot your PC, you usually see a display of memory which shows Conventional and Extended memory. The combination of extended, conventional, and upper memory usually will add up to the total number of memory you have installed on your PC.
Purchasing RAM.
The following table explains the amounts of RAM
per 30 pin and 72 pin SIMM chips.
Table: Courtesy of Kingston Technology Corporation.
Note that a 72 pin SIMM has 4 times the memory of a 30 pin SIMM. Also, note that if you have a "n x 8" 30 pin SIMM, it is a non-parity chip. A "n x 9" 30 pin SIMM is a parity chip. If you have a "n x 36" 72 pin SIMM, you have a parity chip. If you have a "n x 32" pin SIMM, it is a non-parity chip.
It is important to you to know this if you need to purchase memory. As a potential purchaser of memory, READ YOUR USER MANUAL to determine the type of memory you want to replace, or add to your PC.
RAM can come in many types, although main memory is most often DRAM on a SIMM chip. Some of these are: