RAM In All It's Varied Splendor

In some of the previous sections, you've read about the various RAM architectures and styles. In this section we will present to you, the curious consumer, information concerning the various types of RAM used for special purposes. You've probably heard terms like Video RAM and RamBus, but do you know what they mean? Do you care?

If you do, here we intend to enlighten you seekers of truth......

Video RAM (VRAM)

Video RAM (VRAM) is a type of RAM used on video cards, and is used exclusively for video calculations. VRAM stores pixel values for a graphical display, and the boards controller reads these continuously as it refreshes the display. This allows for better video performance without overloading the CPU with an overwhelming amount of video display information.

VRAM is dual-ported, as opposed to DRAM and SRAM, which both have single access ports. One of the VRAM's access ports is used to constantly refresh the display device, while the other is used to change the data to be displayed. This means that VRAM has double the bandwidth of either SRAM or DRAM, and results in faster video performance.

There are numerous forms of video RAM, each used for it's own special case. SGRAM is a very fast form of VRAM used in 3D accelerator card. Windows RAM (WRAM), is specialized for graphic performance, with roughly 25% more bandwidth than VRAM.

Rambus Direct Memory (RDRAM)

Rambus is the newest, hottest form of RAM coming out on the market. Developed by the Rambus Corporation, Rambus Direct RAM (RDRAM) promises to be faster than current memory modules, and will incorporate many features useful for memory intensive computations, such as 3D interfaces, interactive games, and streaming multimedia. RDRAM will be used with Intel microprocessors beginning in 1999. The next computer you buy will most likely use RDRAM. (Bit of trivia: the Nintendo-64 uses RDRAM right now)

So why is it so great? Well, think of it in these terms: from the previous sections, you know that EDO DRAM works at speeds of about 83.3 MHz (officially, only 66MHz). SDRAM, the current speed merchant of RAM, supports bus speeds up to 100 MHz. Not bad. But this is piddly compared with the speeds RDRAM boasts: bus speeds of up to 267 MHz! RDRAM can synchronize itself to the CPU bus, as high as 133 MHZ.

RDRAM provides a 2 byte (16 bit) bus, as opposed to DRAM's 1 byte (8 bit) bus. With a peak RAM speed of 800 MHz, RDRAM can achieve data transfer rates of 1.6 billion bytes per second! (and some tests have clocked it as high as 2 gigs a second). RDRAM also uses pipelining to move data to cache memory closer to the CPU and display devices, further enhancing system performance.

(NOTE: I realize all this talk of bus speeds and RAM speeds may be a little confusing. Allow me to clarify. RAM speed is the speed with which the RAM can access the columns of it's internal data, i.e. how fast it can read and write to itself. Bus speed is the speed with which the RAM transfers data between itself and the various I/O devices and the CPU.)


Question 1

OK, so you, the educated consumer, are at a computer trade show looking to expand the RAM on your mother board. Right now, you have 2 8-meg chips on the board, and you want to by 2 more to bring your machine up to a smashing total of 32. (Woohoo!) While you're wandering the trade show, you see an advertisement for RAMBUS RAM chips. Now, you're eyeing the advertisement, thinking, "Man, I can get 1 32-meg chip, and since it runs at a higher speed, it'll be better overall for my machine!" You look at the price and GADZOOKS! it's $350 a chip! Two 8-meg EDO chips would only cost about $40!

OK, hotshot, what do you do? Do a speed comparison between the 66 MHz EDO chips and the 267 MHz RAMBUS chip. Is the speedup in proportion with the amount of money you'd have to spend to get the chip?


1. Well, first, lets do a speed comparison. Since everything else is equal, we do a speedup equation, with all items but the clock rate cancelling out.

                                            267 MHz
                                            ----------     =  4.05 times faster.
                                             66 MHz

OK, so now we know how much faster it is. Now, is it proportional? Well, I choose to look at this as how much am I gonna pay proportionally. Ignoring the fact that you're buying 16 megs as opposed to 32, we can set it up as:

                                        ---------        =    ~8.75

So, do we play about 9 times more for 4 times the performance?. Probably not....

- This page (c) 1998, Jason Martin -- Last Modified: 12/17/98 -

This page has been created as an academic reference. All sources within have been used without permission for adademic purposes.