Upgrading M571 Memory

72-pin SIMMS (either EDO or Fast Page) are very slow and should not be used, even though four SIMM slots are present on the board. Your memory choices should be limited to PC66, PC100, or PC133 DIMMs in either 64 MB or 128 MB sizes. Use PC100 DIMMs if your front side bus speed is 75 MHz or 83.3 MHz, or if you think you may wish to step up your Front Side Bus speed in the future. Some DIMM memory can run faster than its rated speed, like processors, but memory is so cheap now that it is impractical to attempt savings by skimping on memory speed. Your overclocking attempts will have much greater chance of success with PC100 or PC133 memory. DIMM speed is measured by how long it takes to refresh the memory chips on the stick in nanoseconds (ns). PC66 DIMMs are usually rated at 12ns. PC100 DIMMs must be rated at 10ns or less, though some PC100 memory is rated at 8ns (especially true of high quality memory; you usually get what you pay for). PC133 DIMMs refresh in 7.5ns or less, and the design takes care to avoid signal interference on the DIMM.

128 MB of system memory is usually sufficient for systems using DOS-based operating systems such as Windows 95, Windows 98, or Windows ME. Less performance improvement per MB is seen above 96 MB with these OSs, but today's memory prices make 32 MB DIMMs a poor bargain. You will need more memory if you usually have a number of applications and windows open at one time. The best performance for the money will be obtained from a pair of good quality 64 MB DIMMs that are PC100 and CAS 2.

A short explanation of "CAS": DIMM memory addresses are organized in rows and columns. The CAS (Column Access Strobe) rating defines how many wait states must transpire for the column strobe to be flashed. RAS (Row Access Strobe) and CAS-to-RAS delay are other wait states controlled by the SiS 5597/5598 chipset. Decreasing wait states will usually result in higher system performance, but being too agressive in reducing system timing for CAS, RAS, and CAS to RAS can result in system instability. A CAS of 2 wait states is referred to as "CAS 2", as opposed to CAS 3. CAS 3 is about 3% slower and should be avoided. Of CAS, RAS, and CAS to RAS, CAS is usually the rating that is presented in DIMM descriptions.

Change motherboard chipset settings to use CAS 2 memory by holding down the "home" key at bootup. If the system recognizes CAS 2 memory, the two memory banks reported in the bootup process will be followed by (2t), indicating CAS 2 is set on the chipset. (For faster systems, the "pause" key may be needed to observe the DIMM settings that are applied.) The performance increase supported by CAS 2 is noticable on bootup and during operation and can be verified by benchmark programs, such as Sandra.

Buy only PC100 or PC133 memory. There is usually little price difference between PC66 and PC100 memory. PC100 will not increase system performance, compared to PC66, but if the front side bus speed of the system will be increased at some time, PC100 memory will be required to do this. After installing PC100 or PC133 memory, be sure to change memory access time from 12 ns (required for PC66) to 10 ns in the CMOS settings.

If you use Windows 2000 or Windows XP on your M571 sytstem AND you have an AMD K6 3 processor with its on-chip Level 2 cache, it may be advantageous to install two 128 MB CAS 2 PC100 or PC133 DIMMs for a total of 256 MB of system memory. Not all 128 MB DIMMs will work in an M571; they are not officially supported by PcChips or any available BIOS. Due to the constraints of the M571, a “single sided” 128 MB DIMM will not work. Single Sided 128 MB DIMMs can be identified by their having eight memory chips on one side of the DIMM. The M571 is not able to handle memory chips with this level of density. “Double sided” memory has 8 chips on each side of the DIMM, for 16 chips per DIMM. Some of these DIMMs are logically double sided: The memory chips on them are similar to the ones used on single sided 64 MB DIMMs. These 128 MB DIMMs usually work. But, Some 128 MB DIMMs have 16 memory chips, eight per side, but are arranged to be logically single sided. These 128 MB DIMMs will not work in an M571. I am not able to give an authoritative list of what 128 MB DIMMs do work and which ones do not, so I suggest that if you intend to use 128 MB DIMMs in your M571, you make sure that you can try them out to see if they work first.

A short explanation of Level 2 cache: System memory is relatively slow, compared to the speed of the CPU. Most applications use the same data repetitively, and a memory cache stores this data in mach faster, but more expensive, static ram, or SRAM. SRAM does not need to be continually refreshed, like system RAM. The time that must transpire between CPU accesses are much shorter in SRAM, and the CPU does not need to wait for SRAM to be refreshed constantly, as in system RAM. Caches use algorithms, or mathematical processes, to calculate what data is most likely to be needed by the CPU. The efficiency of the cache is then expressed in its “hit rate”, or the number of times it makes the correct guess as to what data the CPU needs.

The type of Level 2 cache that is used on the M571 motherboard is called “pipeline burst SRAM”. There is 512 KB of Level 2 cache available on the M571 motherboard, enough to cache 128 MB of system memory. At the time the M571 was designed, 128 MB of system RAM was considered to be adequate. Data is stored in the cache by using input and output registers. Reading or writing the initial data block of a task request requires that the CPU wait for 3 cycles, but subsequent reads or writes of that task only take one CPU cycle.

Most CPU chips include an internal cache. This is referred to as “Level 1” cache and was first widely available in the 486 CPU. In AMD K6 2 and K6 3 processors, this Level 1 cache consists of a 32 KB cache for instructions and a second 32 KB cache for data. Both of these caches are 2 way, and work together to form the chip’s Level 1 cache. In addition to this, the K6 3 also includes an on-chip 256 KB Level 2 cache, which can cache up to 4 GB of memory (more than you can use!). When a K6 3 processor is used on the M571, the 512 KB of cache on the M571 motherboard functions as a Level 3 cache. Depending on the applications that are being run, this can result in a significant performance increase, besides the ability to effectively use more than 128 MB of system memory.

Do 128 MB DIMMs actually work? Yes, one of my systems uses a pair of double sided 128 MB PC 100 CAS 2 DIMMs. If you need 256 MB of system memory, use 128 MB DIMMs that you know will work based on the experience of those you trust, or buy DIMMs that you can return if they do not work. Remember, you should have a K6 3 for more than 128 MB system memory, or performance may be degraded by forcing the system to use uncached memory. Set the chipset to take advantage of CAS 2 DIMMs by holding down the "home" key at bootup, as described above.

Virtual memory

Virtual memory is often overlooked when setting up a system, but consideration of virtual memory settings should be given at the beginning of the upgrade process. DOS based (Win 95, 98, & ME) and UNIX-like (Win 2000 and XP) all use virtual memory in their operation. Some data is saved to disk and retrieved when needed, just like some data is saved in system RAM. Windows of all flavors manages the amount of disk space dynamically as the default setting. It is better to manage your own memory settings. Generally, allocate between 1 1/2 to 2 times your system RAM as both the minimum and maximum virtual memory setting. This allocates a specific part of the hard disk for virtual memory and makes hard disk defragmentation more effective.

Virtual memory can also be set up on a separate hard disk that is seldom accessed during normal system use. It is best to use the IDE channel that is less often accessed while your system operates for this disk. For example, if you use your C: drive for most tasks, then place this additional disk on the secondary IDE channel, perhaps with your CDROM drive as a slave. The disk used for virtual memory should be at least a 7200 rpm disk with a 2 MB buffer for performance reasons. Such a configuration will allow faster access to virtual memory.



This page was last modified on 4 MArch 2003