RAM Guide

by Anand Lal Shimpi on November 17, 1997 4:54 PM EST
"#000000">Flash Memory This is a type of EEPROM (see above) that can be reprogrammed in blocks as opposed to regular EEPROM. Many times used in BIOS's, hence the name Flash BIOS.

 

 

MDRAM
Multibank Dynamic Random Access Memory, MDRAM is a type of RAM used in video cards. It is incredibly fast, with transfer as much as a gig per second!

 

 

Parity RAM
Parity and Non-Parity RAM is a classification of your memory modules. If you look on your memory modules and count the chips, if you find an even number of chips (i.e. 1 x 32), you've got Non-Parity RAM. If you've got an odd number (i.e. 1 x 36), its Parity RAM. But what's the difference? Well, the chips on Non-Parity RAM are all memory chips. On Parity RAM, all but one of those chips is a memory chip. So, Non-Parity and Parity RAM both have the same amount of memory addresses. Well, then what's that extra chip for? The other chip on the Parity RAM module is a Parity Bit. This chip checks your flow of data, eliminating errors that would have gone unchecked in Non-Parity RAM. Parity modules are used primarily in servers that cannot crash. If you have a do-or-die situation, Parity RAM might be the way to stop those crashes.

 

 

Page Mode RAM
Also known as FPM RAM, Page-Mode memory allows the line addresses to be dropped if a specific register is in the same row of memory as the previously accessed register. This type of RAM is slowly leaving the market in favor of better types of DRAM.

 

 

PRAM
Parameter RAM. PRAM is used to store settings from the Mac equivalent of Control Panel (whatever that is), even when the computer is turned off. It has a battery to store the information so it's ready at boot up.

 

 

PROM
Programmable Read-Only Memory is written to once and only once and cannot be erased like EPROM. The reason that it is called programmable ROM is that it is actually filled with information after fabrication, so it is in fact programmed. But once it's made, if it's wrong, you have to start all over again.

 

 

RAM
Random Access Memory if you don't know by now. RAM is memory that is constantly updated during your computer usage and loses all of its information when the computer is shut off. It is called random access, because the CPU can access any of the bytes of information in memory without having to access the ones before it.

 

 

RAS/CAS
RAS stands for Row Address Strobe, and logically, CAS stands for Column Address Strobe. Both of these strobes are signals that your CPU or other device (like the processor on your video card) sends to your RAM. They tell a circuit in your RAM module that an address line is correct. In the case of RAS, that the row is correct, or in the case of CAS, that the column is correct.

 

 

RDRAM
An acronym for Rambus DRAM, is a new type of memory from Rambus that promises to takeover the market. See below for more information.

 

 

ROM
Read-Only Memory, ROM cannot be written to like RAM and keeps its information even after the computer is turned off. ROM can also be accessed randomly like RAM. Some of your BIOS settings and like information is what is generally stored in ROM. Standard ROM is written during its fabrication and can never be changed.

 

 

SDRAM
Synchronous DRAM, SDRAM does what BEDO DRAM does all the time (see above). It synchronizes itself with your CPU, with bus speeds up to, maybe even exceeding, 100 MHz. This means that your CPU can get information at every clock cycle! SDRAM can also have access speeds as low as 10 ns!

 

 

SGRAM
Synchronous Graphic RAM, SGRAM offers the amazing capabilities of SDRAM, but for your graphics card. Giving your video the same edge that SDRAM gives your system.

 

 

SRAM
Static Random Access Memory is the alternative to DRAM. SRAM does not need as much electricity for the constant replacing of the memory addresses and goes at a fast rate due that fact that it is not constantly replacing the instructions and values stored inside. The disadvantage to SRAM? It costs more than DRAM. That's the reason your SIMMs are probably DRAM.

 

 

Tag RAM
This is an interesting idea. Tag RAM stores the addresses of any memory in cache. If your CPU finds the address in Tag RAM is looks in the cache, otherwise its back to the memory modules.

 

 

Virtual Memory
You've heard of it, you've worried about it, but what is it? Virtual memory is when your computer uses space on your HDD as memory. This is especially useful when you are running a big program that needs more memory than you physically have. For more information on virtual memory, see the virtual memory section below.

 

 

Volatile/Involatile Memory
Volatile memory is memory which loses its contents when your computer is turned off. Involatile memory does not. ROM is involatile memory.

 

 

VRAM
VRAM is like regular RAM, but it can be accessed simultaneously by the monitor and the processor on your video card so that it can provide smoother graphics. This way, your video card can work with the Quake instructions and the monitor can display them, at the same time!

 

 

WRAM
Window RAM. WRAM allows information to be taken out of RAM at the same time it's being put in. This makes WRAM even more effective than VRAM.

 

Index How much is that Megabyte?

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