RAM Guide

by Anand Lal Shimpi on November 17, 1997 4:54 PM EST
Glossary of Terms

BEDO DRAM | DRAM | ECC | EDO DRAM | EEPROM | EPROM | Flash Memory | MDRAM | Parity RAM
Page-Mode RAM | PRAM | PROM | RAM | RAS/CAS | RDRAM | ROM | SDRAM | SGRAM | SRAM
Tag RAM | Virtual Memory | Volatile/Involatile Memory | VRAM | WRAM

BEDO DRAM
This acronym stands for Burst Extended Data Output Dynamic Random Access Memory. Wow, that's a mouthful. But what does it mean? Well, to find out about Dynamic RAM, see the DRAM section below. To find out about EDO see the EDO section. BEDO DRAM is a special type of EDO DRAM that transfers the information from the RAM memory addresses to the processor at every clock cycle. But, as the name suggests, the RAM is not able to hold up this kind of transfer rate for too long, forcing it to make bursts. These bursts are short, since the RAM simply can't go as fast as your CPU. BEDO DRAM also fails to keep up with bus speeds of over 66 MHz, the theoretical barrier of EDO DRAM anyway. Since RAM generally doesn't keep up with the speed of the chip, your chip has to slow down. These periods are called wait states (see Wait States). The bursts from BEDO DRAM help produce as fewer of these periods.

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DRAM
DRAM stands for Dynamic Random Access Memory. The memory addresses in DRAM need to be "replaced" many times each second. This causes a greater amount of electricity to be used by your RAM and also slows it down, because the RAM addresses are constantly being refreshed. The advantage to DRAM? The price. See the alternative, SRAM, below.

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ECC
Like Parity RAM (see Parity Memory), ECC RAM is used mostly in servers that cannot crash. Short for Error Correction Code, ECC RAM stops crashes due to memory errors. It can correct errors as small as 1 bit!

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EDO DRAM
In case you don't already know, EDO stands for Extended Data Output. Now, if you have a Pentium system or above you've probably heard the praises of EDO DRAM, but what's so great about EDO anyway? Well, unlike regular DRAM which can allow access to only one byte (that's only one instruction or one value) of information at a time, EDO allows an entire block of memory to be moved into the internal cache for quicker access by the CPU. The downside to EDO? Well, theoretically, EDO DRAM can only be used on a bus speed of up 66 MHz. But many have shown the EDO can be used with bus speeds of up to 83.3 MHz. So you could use EDO on your 83.3 MHz x 3 overclocked Pentium MMX. As a side note, EDO DRAM is only effective if your PC supports pipeline bursting. But if your system can handle EDO, it probably supports it too. :)

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EEPROM
This is a type of Programmable Read-Only Memory. Specifically it is Electrically Erasable PROM. EEPROM is able to be erased one byte at a time be being exposed to electricity, hence the name. This allows you to change the information in ROM, but only one byte at a time. Very inefficient compared to flash memory (see below).

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EPROM
Like EEPROM, EPROM is an erasable type of PROM; Erasable Programmable Read-Only Memory. But unlike EEPROM, EPROM is erased by being exposed to ultraviolet light. EPROM is especially useful for fixing last minute bugs in the ROM since it can be easily re-programmed with the proper hardware. But for the user, well, unless you have a PROM burner, you aren't changing it.

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Terms (cont)

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