Ram Essay

RAM
Janelle Ryder
CSNT 121

Your computer stores data in two places: long-term storage (including hard drives and CD-R/RWs) and short-term memory. Storage devices, such as hard drives, maintain data even when they're turned off. Memory, on the other hand, holds onto its contents only when the computer is on and functioning. RAM chips require power to maintain their content, which is why you must save your data onto disk before you turn the computer off. Turn off your computer, and the data in memory vanishes. Temporary memory is referred to as RAM, or random-access memory.

Every time you start your operating system, launch a program, or open a file, the relevant program code and/or data is loaded into RAM. That's why you see RAM listed in the system requirements for the software you buy. If you have more RAM, you can open more files or programs at once and load bigger files or programs onto your system.

There are many different types of RAM out there. The type of RAM doesn't matter nearly as much as how much of it you've got, but using plain old SDRAM memory today will slow you down. There are main types of RAM: SDRAM, DDR and Rambus DRAM.
SDRAM (Synchronous DRAM): SDRAM started out running at 66 MHz, while older fast page mode DRAM and EDO max out at 50 MHz. SDRAM is able to scale to 133 MHz (PC133) officially, and unofficially up to 180MHz or higher. As processors get faster, new generations of memory such as DDR and RDRAM are required to get proper performance.
DDR (Double Data Rate SDRAM): DDR basically doubles the rate of data transfer of standard SDRAM by transferring data on the up and down tick of a clock cycle. DDR is a 2.5 volt technology that uses 184 pins in its DIMMs. It is incompatible with SDRAM physically, but uses a similar parallel bus, making it easier to implement than RDRAM, which is a different technology.

Rambus DRAM (RDRAM): RDRAM is a serial memory technology that arrived in three flavors, PC600, PC700, and PC800. PC800 RDRAM has double the maximum throughput of old PC100 SDRAM, but a higher latency. RDRAM designs with multiple channels, such as those in Pentium 4 motherboards, are currently at the top of the heap in memory throughput.

DRAM comes in two major form factors: DIMMs and RIMMS.
DIMMs are 64-bit components, but if used in a motherboard with a dual-channel configuration you must pair them to get maximum performance. So far there aren't many DDR chipset that use dual-channels. Typically, if you want to add 512 MB of DIMM memory to your machine, you just pop in a 512 MB DIMM if you've got an available slot. DIMMs for SDRAM and DDR are different, and not physically compatible. SDRAM DIMMs have 168-pins and run at 3.3 volts, while DDR DIMMs have 184-pins and run at 2.5 volts.
SODIMM (Small Outline DIMM)
SO DIMMs are commonly used in notebooks and are smaller than normal DIMMs. There are two types of SO DIMMs. Either 72 pins and a transfer rate of 32 bits or 144 pins with a transfer rate of 64 bits.
RIMMs use only a 16-bit interface but run at higher speeds than DDR. To get maximum performance, Intel RDRAM chipsets require the use of RIMMs in pairs over a dual-channel 32-bit interface. You have to plan more when upgrading and purchasing RDRAM.
SO RIMM
Similar in appearance to a SODIMM and uses Rambus technology
Older Memory types:
Fast Page Mode DRAM is plain old DRAM as we once knew it. The problem with standard DRAM was that it maxes out at about 50 MHz.
EDO DRAM:
EDO DRAM gave people up to 5% system performance increase over DRAM. EDO DRAM is like FPM DRAM with some cache built into the chip. Like FPM DRAM, EDO DRAM maxes out at about 50 MHz. Early on, some system makers claimed that if you used EDO DRAM you didn't need L2 cache in your computer to get decent performance. They were wrong. It turns out that EDO DRAM works along with L2 cache to make things even faster, but if you lose the L2 cache, you lose a lot of speed.
BEDO (Burst Extended Data Out)
A step up from the EDO chips. It requires zero wait states and provides at least another 13 percent increase in performance
VRAM (Video RAM)
VRAM is a video version of FPM and is most often used in video accelerator cards. Because it has two ports, It provides the extra benefit over DRAM of being able to execute simultaneous read/write operations at the same time. One channel is used to refresh the screen and the other manages image changes. VRAM tends to be more expensive.
Flash Memory
This is a solid-state, nonvolatile, rewritable memory that functions like RAM and a hard disk combined. If power is lost, all data remains in memory. Because of its high speed, durability, and low voltage requirements, it is ideal for digital cameras, cell phones, printers, handheld computers, pagers and audio recorders.

Shadow RAM
When your computer starts up (boots), minimal instructions for performing the startup procedures and video controls are stored in ROM (Read Only Memory) in what is commonly called BIOS. ROM executes slowly. Shadow RAM allows for the capability of moving selected parts of the BIOS code from ROM to the faster RAM memory.