DDR Memory Questions

dstranathandstranathan
Posted:
in Genius Bar edited January 2014
OK, back in the day when we all used PC100 and PC133 SDRAM, I understood the naming convention for such RAM. PC100 = 100 MHz bus. It was cut and dry. A no-brainer...



But now that we Mac heads are (finally) in the age of DDR memory, I am a little confused on the types of DDR RAM, and the naming convention used to qualify them.



How do the DDR numbers (i.e.; PC2100) correlate to bus speeds? (i.e.; PC2100 isn't used on mobos with *2100* MHz buses).



Can someone explain to me the difference between PC2100 and PC2700 RAM?



Why does apples G4 tech specs page say that the new G4s can use *EITHER* 2100 *OR* 2700 DDR? For example, on older CRT iMacs, Apple never said to use PC133 or PC100 SDRAM.



I am getting ready to buy a new G4 after MWSF and I am going to build a new AMD PC soon too, so I need to get a better understanding of DDR technology!



[ 12-30-2002: Message edited by: dstranathan ]</p>

Comments

  • Reply 1 of 7
    gargoylegargoyle Posts: 660member
    Overview

    First off let's run down what the different speed ratings of DDR SDRAM mean.



    PC3500 = 433MHz DDR = 216.66MHz Memory Bus



    PC3200 = 400MHz DDR = 200.00MHz Memory Bus



    PC2700 = 333MHz DDR = 166.66MHz Memory Bus



    PC2400 = 300MHz DDR = 150.00MHz Memory Bus



    PC2100 = 266MHz DDR = 133.33MHz Memory Bus



    PC1600 = 200MHz DDR = 100.00MHz Memory Bus





    Source: <a href="http://www.ocaddiction.com/reviews/memory/3200roundup/"; target="_blank">http://www.ocaddiction.com/reviews/memory/3200roundup/</a>;





    Hope this helps
  • Reply 2 of 7
    alcimedesalcimedes Posts: 5,486member
    excellent post Gargoyle. informative and concise.



    thanks!
  • Reply 3 of 7
    dstranathandstranathan Posts: 1,717member
    [quote]Originally posted by Gargoyle:

    <strong>

    PC2700 = 333MHz DDR = 166.66MHz Memory Bus

    </strong>

    <hr></blockquote>



    OK, I understand the math involved in 333 MHz DDR RAM using a 166.66 bus (166.66 x 2 = 333). After all, the memory is DOUBLE data rate. Makes sense...



    But how the heck does the number 2700 fit into the scheme of things? Why not just call the RAM "PC333"?



    Thanks for the post!
  • Reply 4 of 7
    alcimedesalcimedes Posts: 5,486member
    simple, if i had to guess.



    marketing.



    2700=bigger than 333.
  • Reply 5 of 7
    microtrashmicrotrash Posts: 57member
    Simple ! 2700 is the.... bandwith ! yes, this kind of ram is suppose to handle 2700MB per second, or 2.7GB/sec.



    Because of the RAMBUS, PC1xx and the DDR standart, someone decide to call RAM by it bandwith for give consummer a greater understanding and comparaison method. You know, rambus run at 400mhz (now 533mhz) and is slower (in term of bandwith) than DDR at 266mhz !! And RAMBUS is called PC800 (the 400mhx ones) and PC1066 (the 533mhz one). So for now, the number after the "PC" mean the bandwith.



    [ 12-31-2002: Message edited by: microtrash ]</p>
  • Reply 6 of 7
    lucaluca Posts: 3,833member
    Rambus isn't always 800 MHz or 1000 MHz... each stick is 200 MHz or 250 MHz, and the speed is found by adding them all up. You must have two sticks in order to get any speed benefit. In order for full speed, you have to have all four. There's "1600 MHz" RDRAM coming out, but that's just because it supports 8 sticks now instead of 4.



    Anyway, RDRAM/Rambus is a crock.
  • Reply 7 of 7
    microtrashmicrotrash Posts: 57member
    [quote]Originally posted by Luca Rescigno:

    <strong>Rambus isn't always 800 MHz or 1000 MHz... each stick is 200 MHz or 250 MHz, and the speed is found by adding them all up. You must have two sticks in order to get any speed benefit. In order for full speed, you have to have all four. There's "1600 MHz" RDRAM coming out, but that's just because it supports 8 sticks now instead of 4.</strong><hr></blockquote>

    ?? That's does'nt make any sense... so if you put 4 DIMM you get full speed ?? nah. Because on the first RAMBUS motherboard there was a bug that force intel to pull the 4th RAM slot. And computer aren't go slower for that. Anyway, PIV front-side bus is now 533mhz, in par with mem bus. If you put one DIMM, (most of the people do that for furter expension) that's not logical to have only a 133mhz bus... I know that RAMBUS mem is serial (8bits or 16bits wide) instead of parallel (and 32 , 64 or 128bits wide), and that's why it go at 400mhz : to compensate speed, but it would be a big marketing error to make RAMBUS as you describe.. it's worst than 9600's interleaved memory gag....

    [quote]<strong>

    Anyway, RDRAM/Rambus is a crock.</strong><hr></blockquote>

    Agree ! Slower and $$



    [ 01-01-2003: Message edited by: microtrash ]</p>
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