Some fundamental concepts

The Rambus does not work to 800MHz

What is better: Rambus or PC133?

The chipset i820 and his problems of memory

PC133, Apollo Pro 133, BX and KX133


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Memoirs and chipsets at the beginning of 2000


On the following pages we are going to study the current situation of two of the most important elements of the computer: the memory RAM and the chipset of the motherboard. Does he feel confused when he reads things like PC133, RDRAM, SDRAM, DDR, i820, KX133? Do not worry, keep on reading and it will see that it is not so complicated...


Module of memory SDRAM in format DIMM

Some fundamental concepts

To understand what comes next, we must clarify first the meaning of some "basic" terms:

  • RAM or DRAM: the principal memory of the computer, this 32, 64, 128... MB (megabytes, "gentle") that appear in the computers announcements. In modern operating systems type Windows, the speed and especially the RAM quantity is a determinant factor of the yield.
  • SDRAM: or Synchronous DRAM, the type of memory more used at present.
  • PC66: the memory SDRAM that works to 66 MHz. At present only it is used in the Celeron.
  • PC100: the memory SDRAM that works to 100 MHz. Nowadays it is most used (K6-2, K6-III, K7 Athlon, modern Pentium II and Pentium III).
  • PC133: the memory SDRAM that works to 133 MHz.
  • RDRAM or Rambus DRAM: a new type of memory, of design completely different from that of the SDRAM; theoretically it offers better yield.
  • DIMM: module of memory SDRAM (or, formerly and in exceptionally rare cases, of memory EDO).
  • RIMM: module of memory RDRAM (Rambus).

To avoid confusions between S-dram and R-dram, we will try to speak of "PC100", "PC133" and "Rambus". If you want to know more on these topics, consult in the column of the left the Related Topics. And saying this, there we go...


The Rambus does not work to 800 MHz

Or at least not likewise the SDRAM. The memory SDRAM, good is PC66, PC100 or PC133, it has a breadth of equal bus of information to 64 bits, what means that in every cycle of clock (every Hz) he sends 64 bits = 8 bytes. Thus his capacity of transference of information (that is to say, his useful speed) will be:

   PC66: 8 bytes / cycles x 66 MHz = 533 MB/s

   PC100: 8 bytes / cycles x 100 MHz = 800 MB/s = 0,8 GB/s

   PC133: 8 bytes / cycles x 133 MHz = 1066 MB/s = 1,06 GB/s

More rapids turn the microprocessors (and some of them work already to almost 1.000 MHz), more important it proves to have a fluid communications channel between these and the memory, something that also is important so that the textures storage in the principal memory with a graphic card AGP 4x is really effective.

The RDRAM or memory Rambus appeared like a solution to this need, by means of a completely new design. The Rambus has a narrower bus of information, of only 16 bits = 2 bytes, but it works at much major speeds, of 266, 356 and 400 MHz. Also, it is capable of making use of every sign doubly, so that in every clock cycle he sends 4 bytes instead of 2.

Due to this double use of the sign, it is said that the Rambus works to 600, 712 and 800 "virtual" or "equivalent" MHz. And for commercial motives, it is named PC600, PC700 and PC800 (it seems that "PC533" y "PC712" they do not please to the experts in marketing). For all this, his transference capacity is:

   Rambus PC600: 2 x 2 bytes / cycles x 266 MHz = 1,06 GB/s

   Rambus PC700: 2 x 2 bytes / cycles x 356 MHz = 1,42 GB/s

   Rambus PC800: 2 x 2 bytes / cycles x 400 MHz = 1,6 GB/s

Since we see, the most powerful Rambus (that of "800 equivalent MHz") can transmit the information double that the SDRAM PC100, what is not small... but it is not eight times any more, how many publicists like making to believe.


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