Statements About Memory Are Recalled, Corrected
Last week’s Customer Service column erroneously said that Intel’s Pentium microprocessor addresses memory in 32-bit units. It addresses memory in 64-bit units.
The column also said that Pentium performance is not affected if a computer has a single RAM memory chip module instead of two. There are Pentium computers made with single RAM modules whose performance would be enhanced merely by adding another--but such machines are rare. In fact, most Pentium computers will not run if they have only one memory module installed, according to Intel Corp. spokesman Chris Lane.
The most popular form of RAM memory is a SIMM (single in-line memory module), which is about 4.25 inches wide, has 72 connectors and a 32-bit address width. Details of how the Pentium works in a particular computer are controlled by a companion chipset, the most popular being Intel’s Triton chipset. The Triton requires that SIMMs be installed in pairs to provide a 64-bit memory-address width.
At least one non-Intel chipset allows Pentiums to run with one SIMM module, Lane said. That slows the Pentium’s performance because it has to call the SIMM twice to obtain the needed 64 bits of data. RAM chips respond much slower than the Pentium can process data, so the Pentium is forced to idle while the extra requests are being met in a single SIMM computer.
Some of the latest-design Pentium computers, however, actually enhance performance by using memory chips installed in units of one, not pairs. But they use a DIMM (dual in-line memory module), which is twice as wide as a SIMM and has a 64-bit address.
Even though the Pentium addresses memory in 64-bit swaths, it normally processes data 32-bits at a time. Some tasks, such as decimal number calculations, are done in 64-bit units.
In addition to RAM memory, Pentium chips also communicate with the memory cache chips and the supporting chipset in 64-bit units. The chipset then communicates at 32 bits through the PCI bus with the video card, disk drives and other PCI peripherals. The slowest communication takes place between the chipset and the keyboard, mouse and peripheral port.
Richard O’Reilly, The Times’ director of computer analysis, will answer questions of broad interest in this column. E-mail questions to [email protected], fax to (213) 237-4712, or mail to Answers c/o Richard O’Reilly, Business Editorial, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053.
