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Thread: Memory FAQ

  1. #1
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    Lightbulb Memory Reference

    Memtest
    - command line utility to test 'most' of the available memory (but not all). Can be run in Single User Mode and test all but about 60MB RAM.
    Rember
    - GUI version of memtest (4.05 currently)

    Disk Test (Hard-Diskcorruption_test Folder.sit). http://www.gballard.net/macrant/ram.html
    http://www.macintouch.com/g5reader07.html#jan08

    MacIntouch BAD RAM Report
    More about reseat RAM, using a pencil eraser to clean contacts, and to be careful when installing RAM in G5s.

    DIMM First Aid
    DIMM First Aid 1.2 on Version Tracker

    - A great explanation of why and what SDRAM specs and Apple's G4 firmware are all about, with note about chips per bank, and compatible systems (only for PC100/133, not compatible with DDR or PC2100 or later).

    DFA was developed after Apple G4 firmware update started requiring the SPD code be present in order to be used. If SPD is present, DFA returns "OKAY" otherwise it will try to "repair" or not present, as well as tell you what is found.
    Don't take "OKAY" as meaning it passed any other testing.

    MacInTouch "Bad RAM?"
    Crucial Library
    Crucial Memory Glossary
    Crucial FAQ
    Crucial: Apple Selection Guide

    Ars: Understanding Latency and bandwidth

    <UL TYPE=SQUARE><LI>How RAM works
    <LI> Simmtester.com: Understanding DDR Serial Presence Detect (SPD) Table
    <LI>Crucial Technologies Support page
    <LI> Crucial KB
    <LI>Kingston Technology's Ultimate Memory Guide
    <LI>Micron Technology DRAM Product Guide
    <LI>Samsung Semiconductor's Support web page
    <LI>How Stuff Works: DDR RAM
    <LI>Tom's Hardware Guide: DDR SDRAM
    </LI>
    http://www.apple.com/support/ibook/
    iBook Upgrades
    PDF Manual: Adding RAM Customer Installable Parts
    iBook Specification
    iBook Discussions
    SO-DIMM specifications
    RAM modules for Apple notebooks

    G5 Memory Specs Apple KB #86414
    Apple Developer Note G5 Memory

    PPCNUX - Memory Performance Benchmark
    System Profile should show if they are working as one. I assume it enables DDR or 128-bit vs 64-bit.
    G5 test bus utility download
    iMac G5 RAM Upgrade
    MacMini RAM Expansion

    Apple Tech Note QA1191 PC2700 in MDD
    PowerMac G4 Dev Note

    Legacy OldWorld Mac DIMMs
    SDRAM
    DDR DRAM
    DDR2 DRAM
    Last edited by TZ; 06-23-2007 at 06:05 AM.

  2. #2
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    Lightbulb

    DIMM First Aid ver. 1.2
    The above version of DFA was developped using the PowerMac G4 series adopting the UNI-NORTH chipset as memory controller and IC circuit, under OS9.x.

    Due to the above, all previos Mac models using the Motorola MPC106 (a.k.a. GRACKLE), or previous memory controllers chipsets may return a DFA diagnosis stating:
    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> DIMM reads an old or incompatible page number<HR></BLOCKQUOTE> Other than that, the DFA report is correct.
    DFA runs under OS9.1 or later (it won't run properly under OSX).

    DIMM First Aid

    DIMM First Aid is an application for checking and repairing the settings in the SPD EEPROMs on SDRAM DIMMs.

    Send any feedback or bug reports to dfa@mactcp.org.nz

    DIMM First Aid 1.2 is now available. Version 1.2 adds support for the QuickSilver G4, and can now check DIMMs on the Beige G3. Reporting the speed of PC133-222 DIMMs has been fixed. DIMMs that are incompatible with newer Macs are no longer reported as incompatible on the Beige G3 and B&W G3.

    New in DIMM First Aid 1.1: support for the new iBook, can now check DIMMs on the PowerMac G3 B&W and the PowerMac G4 PCI graphics, and reports the speed rating for DIMMs. Version 1.1 also checks for DIMMs that use chips that are incompatible sizes, such as 64Mx4 chips used on single bank 512MB DIMMs and 32Mx4 chips used on single bank 256MB DIMMs.

    Incompatible 256MB and 512MB DIMMs: 256MB DIMMs made from one bank of 16 32Mx4 chips and 512MB DIMMs made from one bank of 16 64Mx4 chips are not compatible with the G4 AGP Graphics, the slot loading iMac, and later models of Mac. They will only work in the Beige G3, the B&W G3, and the G4 PCI Graphics. If you are buying a 256MB or 512MB DIMM and you are not sure if it will work on a Mac, do not buy DIMMs that have a single bank made from 16 chips, make sure it has two banks of 8 chips each, or for 256MB DIMMs one bank of 8 chips or two banks of 4 chips are also OK.

    Incompatible DIMMs may also be identified as having 32Mx4 chips (for a 256MB DIMM) or 64Mx4 chips (for a 512MB DIMM). DIMM First Aid will identify these DIMMs as having an incompatible number of column address bits. DIMM First Aid can not fix these DIMMs.
    Last edited by TZ; 03-21-2005 at 08:14 AM.

  3. #3
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    Default

    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>The importance of removing "bad" RAM from your Mac

    One of the most common culprits of general system instability, problems installing or re-installing Mac OS X, and various other issues is defective RAM. Mac OS X 10.2.x in particular has been noted as being "picky" about installed memory.

    You can easily determine if you have a "bad" RAM module by using the Apple Hardware Diagnostic CD, included with all currently shipping Macintosh models. To use the Apple Hardware Test CD, restart your computer while holding down the C key until the "Loading..." icon appears.

    Note that the Apple Hardware Test can not be used when a mouse is directly connected to the USB port on the display or on the iBook. Apple says "Please connect the mouse to a USB keyboard."

    Our friend Erin Duckhorn at Crucial Memory writes "With the cost of RAM being so low (across the board), people often think that all RAM is the same and they can get by purchasing the cheapest RAM out there. Not true! Stability and performance are directly tied to the quality of RAM used. This is particularly important for Mac users who tend to use very memory-intensive software."

    Duckhorn also pointed us to a document on the Crucial Web site that describes "top tier" and "generic" memory:

    * Top Tier Memory After going through this extensive series of tests, you can be confident that the passing parts will work for a long time.

    * Generic Memory So what happens to the parts that failed testing? Some get thrown out, but many are re-tested and graded to lesser speeds and/or conditions (i.e. without guard bands).

    Others aren't even re-tested (even though they might not have gone through burn-in). Yes, these lower-grade modules will probably work today, but they're more prone to marginal performance and failures, especially over time.

    DRAM manufacturers often sell this memory to third party vendors who then re-label them with their own brand name.

    Unfortunately, it appears that Apple semi-frequently ships Macs with at least somewhat defective RAM modules. Apple does not disclose its component suppliers.



    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>While browsing through the eJournal of Dan Gillmor, an editor with the San JOse Mercury News, we found this case example of a "bad" RAM headache:

    "I have a dual-processor G4, 800 MHz, purchased new. For nearly a year I had intermittent crashes, freezes, memory problems, app shutdowns, you name it. I reinstalled the entire system numerous times. 75% of the time I couldn't even get the OS reinstalled, I'd have to try 3-4 times to reinstall it. I could never get a good incremental upgrade past 10.2.3. It was very frustrating.

    "One day about a month ago, I was pawing through the stack of disks that Apple provided with the computer, which I had never opened. It was the HW diagnostic disk. I decided 'What the hey' and ran it. Immediately it identified that I had a bad RAM DIMM. I remembered that I had mail-ordered a new DIMM about the time that the crashes started.

    "I removed the DIMM, going back down to 512MB, and all was immediately well. I then went out and purchased another new 512MB DIMM locally at a store (in case it was bad and I needed to return it). Installed it and all has been well since. I have not had a single crash, kernel panic, or any other (strange) behavior since [...]"<HR></BLOCKQUOTE> www.macfixit.com <HR></BLOCKQUOTE>

  4. #4
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    Lightbulb Terminology

    Memory Types
    Cache: static random access memory containing recently used information
    DRAM: dynamic random access memory
    SDRAM: single data rate synchronous dynamic random access memory
    DDR SDRAM: double data rate synchronous dynamic random access memory. Usually referred to as DDR.
    SLDRAM: synchronous link dynamic random access memory
    RDRAM: Rambus dynamic random access memory
    RAM: random access memory
    ROM: read only memory (permanent memory that cannot be changed)
    SRAM: static random access memory
    SDRAM can and is also described as DIMM as well.
    168-pin DIMM

    Approximately 5.25 in. by 1.375 in. (133.35 mm by 34.92 mm)

    A dual inline memory module (DIMM) consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold pins on the bottom of the DIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a DIMM are not connected.

    168-pin DIMMs are commonly found in Pentium¬ and Athlon¬ systems. 168-pin DIMMs are available in EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM. When upgrading, be sure to match the memory technology that is already in your system. (Information about which memory technology your system uses is included in the Crucial Memory Advisor» tool.)

    The number of black components on a 168-pin DIMM can vary, but it always has 84 pins on the front and 84 pins on the back, for a total of 168. 168-pin DIMMs are approximately 5.25 inches long and 1.375 inches high, though the heights can vary. They have two small notches within the row of pins along the bottom of the module. Crucial SDRAM PC100
    _________________________
    DDR
    Double data rate is a type of SDRAM in which data is sent on both the rising and falling edges of clock cycles in a data burst. It is usually referred to as DDR as opposed to DDR SDRAM.

    DDR2 Like DDR, DDR2 is a type of SDRAM in which data is sent on both the rising and falling edges of clock cycles in a data burst. DDR2 is the next evolutionary step in the DDR infrastructure and has additional features built into it to allow for increased system performance.

    DIMM Dual inline memory module. A module with signal and power pins on both sides of the board (front and back).

    DRAM Dynamic random access memory. A type of memory component used to store information in a computer system. "Dynamic" means the DRAMs need a constant "refresh" (pulse of current through all of the memory cells) to keep the stored information. (See also RAM and SRAM.)

    Dynamic Type of RAM (random access memory). To keep data in the DRAM, this data needs to be "refreshed" (recharged). The electric charge fades out of a DRAM like air seeps out of a balloon. Because of this change, it is called "dynamic."

    EDO Extended data out. An asynchronous DRAM operating mode that improves access times compared to fast page mode (FPM) DRAMs.

    Synchronous Memory Memory that has its signals synchronized with the system clock. SDRAM and DDR are examples of synchronous memory types.

    SDRAM Synchronous dynamic random access memory delivers bursts of data at high speeds using a synchronous interface. Its is actually SDR SDRAM (single data rate SDRAM) but is usually used to referred to as just "SDRAM."

    RAM Random access memory. A data storage device for which the order of access to different locations does not affect the speed of access, except for bursts. Data is typically stored in RAM temporarily for use by the process or while the computer is operating. FPM, EDO, SDRAM, DDR, etc. are all types of RAM.

    PC100 The PC100 specification defines the requirements for SDRAM modules used on 100MHz FSB motherboards.

    PC133 The PC133 specification details the requirements for SDRAM modules used on 133MHz FSB motherboards. PC133 SDRAM can be used on 100MHz FSB motherboards but will not yield a performance advantage over PC100 memory at 100MHz.

    http://support.crucial.com/library/glossary.asp#D
    __________________
    quote:<hr> ECC - Error correcting code. Logic designed to detect and correct memory errors.

    Buffered Memory - A buffer isolates the memory from the controller to minimize the load on the chip set. It is typically used when the system has a high density of memory and/or when a system has more than 3 memory module sockets.

    Registered Memory - Registers delay memory information for one clock cycle to ensure all communication from the chipset is collected by the clock edge, providing a controlled delay on heavily loaded memories.

    What does "registered" SDRAM mean?
    The term "registered" refers to how the memory module processes signals. Registered modules contain a register that delays all information transferred to the module by one clock cycle. This type of memory is primarily used in servers and was designed for modules with 32 or more chips on them to help ensure that data is properly handled.

    While most PCs will accept only unbuffered SDRAM, there are some that accept registered SDRAM. Keep in mind that when you install registered SDRAM, all of the modules installed in your PC must be registered because unbuffered and registered modules are not interchangeable.

    You can tell if you are using registered memory by looking at one of the modules currently installed in your system. If it has one or more small black chips mounted horizontally on the module, you have registered memory. If not, you have unbuffered memory.
    http://www.crucial.com/kb/answer.asp?qid=3669

    What is the difference between buffered and registered memory?
    DDR and SDRAM can be unbuffered or registered. Buffered modules contain a buffer to help the chipset cope with the large electrical load required when the system has a lot of memory. Registered modules do not have a buffer but do contain a register that delays all information transferred to the module by one clock cycle. Buffered and registered modules are typically used only in servers and other mission-critical systems where it is extremely important that the data is properly handled.
    http://www.crucial.com/kb/answer.asp?qid=3682

    Is unbuffered memory faster than registered?
    Yes, unbuffered memory is faster than registered memory. The register in registered memory delays all information transferred by one clock cycle, slowing the overall system performance.

    Most systems are designed to take either registered or unbuffered memory, and the two are not interchangeable. If your system takes registered memory, it probably won't work if you try to replace the registered memory with unbuffered memory.
    http://www.crucial.com/kb/answer.asp?qid=3727

    Is all registered SDRAM also ECC?
    The industry standards for registered SDRAM and DDR modules do not require that the modules have ECC functionallity. However, the vast majority of computer and motherboard manufacturers, when implementing registered memory in their products, make ECC a requirement of the registered SDRAM and DDR modules. As a result, all of the registered SDRAM and DDR we sell at Crucial.com is also ECC. http://www.crucial.com/kb/answer.asp?qid=3744

    Is non-parity the same as non-ECC?
    Yes, the terms "non-parity" and "non-ECC" are both used to describe memory that does not have any error detection or correction abilities. Some people use "non-parity" for FPM and EDO memory and "non-ECC" for SDRAM and DDR memory. In order to avoid confusion, at Crucial we usually use the term non-parity for all modules without error detection capabilities.
    http://www.crucial.com/kb/answer.asp?qid=3726

    What do 16x64 16x72 etc. represent when describing memory?
    If you are shopping through Crucial's advanced search or are shopping by motherboard, you may see the size of your module written in the format 16Meg x 64, 16Meg x 72, etc. In this format, the second number gives the width of the data path in bits. If this number is divisible by nine, it is a parity or ECC module; otherwise, it is a non-parity module.

    You can determine the size of your module from this format by multiplying the two numbers together, then dividing by eight or nine, whichever results in an even number. This gives you the size of your module in megabytes (MB).
    http://www.crucial.com/kb/answer.asp?qid=3684
    Crucial KB <hr>
    ECC is a Very Good Thing. Doesn't overclock, but that's not what you want it for. Speed wise, ECC == Non ECC assuming same bus & timings. Stability wise...well ECC is for being stable, Non ECC is for being cheap. ECC caters to workstation/server users, whereas the non-ECC is designed to impress gamers and desktop users.
    Last edited by TZ; 09-30-2005 at 11:24 AM.

  5. #5
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    Lightbulb BAD RAM: memory testing methods

    [Sam Herschbein] In the old core memory days, memory diagnostics were designed to test the bit matrix and supporting electronics for electro-magnetic interference. The coders knew the number of wires for the sides of the matrix and how they translated to memory addresses. The tests were then designed to cause the maximum amount of interference possible. When running memory diagnostics, you would hear the memory board's noise change during the different phases of the tests. [...]

    Today, common memory module tests operate sequentially through memory, thrashing bits with selected patterns at a given address and then stepping to the next sequential address. This will not be likely to find most errors generated by electro-magnetic interference.

    Assuming my scenario is valid: A newly modified piece of the OS [e.g. Panther] has the particular bit and memory address read/write pattern(s) that cause electro-magnetic interference errors in a particular module/chip set.
    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Jeff Bagby shared some more notes about static discharges, memory problems and serious issues for computer reliability:

    On Ric's comment that his PowerBook Pismo G3 may have RAM that deteriorated over the years, I recall that Apple in the past really hammered home the problems caused by static discharge.

    In a video tape as part of my Apple Service training 12 years ago, Steve Wozniak discussed how damage caused by static electricity could take years to manifest itself noticeably. In the tape, he (and I think he is the one who made the following point) said that if you can feel a static pop, it is at least 3,000 volts (but low amperage).

    A discharge of only 10 volts, however, can destroy or damage a logic circuit.

    Make sure you are well grounded, and wearing only natural fiber (non wool) clothing (no synthetics) anytime you open a computer or handle any components.

    [While I always follow those precautions when opening or modifying a computer, I didn't expect such serious problems would be caused just by using a laptop in a low-humidity environment, but I think static discharges through the keyboard likely caused the slow deterioration of the memory card. I subsequently replaced the top card - just under the keyboard, while retaining the lower card, and no problems appeared while running Apple's Hardware Test CD. -Ric Ford] <HR></BLOCKQUOTE>
    Sound familiar? <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>If your computer is having persistent stability problems, it may be bad RAM. Now that Windows is a bit more stable than it was back in the bad old days, Microsoft would like to give users a way to point the finger back at their own hardware if their computer is acting up. It released a memory diagnostic utility yesterday. Windows Diagnostic Utility <HR></BLOCKQUOTE>
    Last edited by TZ; 02-24-2005 at 06:51 AM.

  6. #6
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    Lightbulb RAM comparison

    Dear Kaye,

    Quote Originally Posted by kaye
    Oh and while I'm begging Costa, how does the RAM compare in speed to MDD RAM or G5 DP RAM, or what Mac RAM does it compare to? k
    A very good question and a hard question to answer with appropriate "easy-to-understand" language. (Besides: I am still learning).

    Well, then.... let's give it a try:
    Typicall SDRAM modules, like the ones we have been using up to the PowerMac QS series, operate strictly in accordance to a JEDEC standard where RAM cells' information is handed to the Memory Controller (or "Chipset") during the rising - or the "top electronic wave" - of a system Clock Cycle. The Clock Cycle is generated by the Memory Controller and it "happens" along the Front System Bus (= FSB - an electronic in-printed circuit in our motherboards, connecting the Chipset [MC] to the other internal peripherals & components inside our 'puter).
    I'll try to make a quick sketch of the above data transfer:

    ---------[**]--------------[**]----------->
    ____|=====|_____|======|_______>

    Where [**] = the data being transfered, and the "bumps" indicating the clock cycle "wave" or rising.

    O.k. so far? Are you with me? The above is how data is transfered with traditional SDRAM devices (PC100 or PC133 stuff).

    From the MDD PowerMac onwards, DDR SDRAM made its appearance even in the Mac world. This because of the traditional frequency limitation SDRAM modules are bound to, due to their very architecture. With ever faster CPUs and general speed growing needs, it is obvious that future computers will need even faster RAM capable of coping with FSB clock frequencies well in excess of 133MHz.
    One easy way out of this limitation was to desing a SDRAM device capable of quickly handle doubling frequencies and the idea of DDR memory soon was made reality.
    By adding 16 pins more than the traditional SDRAM module, the DDR RAM module was created and the devices mounted on such module are capable to hand over to the Memory Controller information during *BOTH* the rising and falling edges of the Clock Cycle frequency "wave"; i.e.:

    _____|=========|________|=========|_______>
    -------[**]---------[**]-----------[**]---------[**]-------->

    (I apologise for the rudimentary sketch, but I hope you'll get the idea just the same).
    This symple idea has allowed technicians to provide instantly RAM devices capable of delivering their information stably at double the frequencies they used to have before.
    To use such DDR RAM modules though, you need an 184-pin capable RAM bus on the mother board and a Memory Controller (or Chipset) capable of "collecting" the informations coming from the RAM cells at the right moment along the "Clock Cycle wave" it has generated on the FSB.

    The DRAM devices you have asked me to look for, belong to the SDRAM kind; i.e.: they send their data only ONCE per Clock Cycle.

    Last edited by TZ; 02-24-2005 at 07:02 AM.

  7. #7
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    Lightbulb

    Mis-programmed SPD is most likely a major factor in RAM incompatibility. Perhaps there is a way to over-ride RAM settings in Open Firmware (similar to changing BIOS) which can be used to reduce how much physical RAM is seen in a system, not sure about changing SPD settings.

    Here's the spec page:
    The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR400-compliant (PC3200).

    DDR333 (PC2700) or slower DIMMs do not work in the Power Mac G5 computer.

    DIMMs with any of the following features are not supported in the Power Mac G5 computer: registers or buffers, PLLs, ECC, parity, or EDO RAM.

    Mechanical Specifications

    The mechanical design of the DDR SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b. To find this specification on the World Wide Web, refer to ñRAM Expansion Modulesî .

    The maximum height of DIMMs for use in the Power Mac G5 computer is 2 inches.

    Electrical Specifications

    The electrical design of the SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b. To find this specification on the World Wide Web, refer to ñRAM Expansion Modulesî .

    The Serial Presence Detect (SPD) EEPROM specified in the JEDEC standard is required and must be set to properly define the DIMM configuration. The EEPROM is powered on 3.3 V. Details about the required values for each byte on the SPD EEPROM can be found on pages 68?70 of the JEDEC specification.
    Important

    For a DIMM to be recognized by the startup software, the SPD feature must be programmed properly to indicate the timing modes supported by the DIMM.

    DIMM Configurations

    The largest DIMM supported is a two-bank DIMM of 1 GB using 512 Mbit DDR SDRAM devices. The maximum number of devices per DIMM is 16.
    Important

    Power is delivered to the Power Mac G5 during sleep mode, so do not remove DIMMs while in sleep mode. A red light adjacent to the DIMM is illuminated when the duct door is removed and power is present.

    Table 4-1 shows information about the different sizes of DDR SDRAM devices used in the memory modules. The memory controller supports 64 Mbit, 128 Mbit, 256 Mbit, and 512 Mbit DDR SDRAM devices. The device configurations include three specifications: address range, word size, and number of banks. For example, a 1 M by 16 by 4 device addresses 1 M, stores 16 bits at a time, and has 4 banks.

    The first column in Table 4-1 shows the memory size of the largest DIMM with that device size that the computer can accommodate. The third column specifies the number of devices needed to make up the 8-byte width of the data bus. The fourth column in the table shows the size of each bank of devices, which is based on the number of internal banks in each device and the number of devices per bank.
    G5 Memory Specs Apple KB #86414
    Apple's PDF on G5 Memory

    Lots of chatter over at Apple forums about this,
    Apple Discussions: biggest thread on G5 memory
    Last edited by TZ; 02-24-2005 at 06:46 AM.
    molṑn labe'
    "I am a mortal enemy to arbitrary government and unlimited power. I am naturally very jealous for the rights and liberties of my country, and the least encroachment of those invaluable privileges is apt to make my blood boil."
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  8. #8
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    Lightbulb Memory Management in OS X

    Introduction to Memory Performance
    Apple Developer Notes

    Memory Management in Mac OS X

    Efficient memory management is an important aspect of writing high performance code in Mac OS X code. Tuning your memory usage can reduce both your application’s memory footprint and the amount of CPU time it uses. In order to properly tune your code though, you need to understand something about how Mac OS X manages memory.

    Unlike earlier versions of Mac OS, Mac OS X includes a fully-integrated virtual memory system that you cannot turn off. It is always on, providing up to 4 gigabytes of addressable space per process. However, few machines have this much dedicated RAM for the entire system, much less for a single process. To compensate for this limitation, the virtual memory system uses hard disk storage to hold data not currently in use. This hard disk storage is sometimes called the “swap” space because of its use as storage for data being swapping in and out of memory.
    Note: Unlike most UNIX-based operating systems, Mac OS X does not use a preallocated swap partition for virtual memory. Instead, it uses all of the available space on the machine’s boot partition.

    The following sections introduce terminology and provide a brief overview of the Mac OS X virtual memory system. For more detailed information on how the Mac OS X virtual memory system works, please see Inside Mac OS X: Kernel Programming.

    Performance: Managing Memory

  9. #9
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    Lightbulb G5 - mixing RAM

    Apple RAM (Hynix) in J11, J12
    - Apple Hardware Test all passed (works fine)

    Crucial (3rd party) RAM in J11, J12
    - Apple Hardware Test all passed (works fine)

    Apple RAM in J11, J12, and Crucial in J13, J14
    - AHT test failed -froze up.
    Mac only runs for like 1/2 - 1 hour.
    Constantly freezes and forces shut down.

    Crucial RAM in J11, J12, and Apple RAM in J13, J14
    - AHT test failed upon memory testing: **ERROR CODE** 2MEM/1/4IMM2/J13 **ERROR CODE**
    The Mac runs okay and doesn't lock up but still have some persistent problems.

    As re-emphasized here, the best first step toward resolving this issue is to try moving your pairs of RAM to alternate slots, or entirely removing a pair (or two) of RAM.

    Rev B G5s have tighter tolerances and more exacting standards but you can be sure everyone, MacGurus, Crucial, etc. are busy testing. The new firmware update has resulted in OEM RAM not showing up or working in some cases.

    Power Mac G5 Uniprocessor Firmware (#6): Problems with RAM, switching modules, fix on the way? Apple Discussion

    "The firmware update sets the specs for the RAM closer so some of them will not work after the update. This depends on the manufacturer and/or the date of manufacture. This explains why for some users it works fine and for others it causes this mess. Anyway, in the case of the RAM breakdown apple will send new ram for free and all you do is ship back the damaged ones after receiving the new ones."

    If you are covered under an Apple warranty or through the Apple Care program and are experiencing problems with Apple-supplied, original RAM, you may want to try contacting the appropriate department for a possible replacement.
    ---------------
    RE: Problems w/ Crucial RAM in G5 2.0 Rev. B

    Here is what I replied to jhersco:

    -------------------
    As you have seen from looking at the threads posted in Apple's forums (you may have seen a few posts from me), our memory is completely compatible with the G5. However, there have been a few (less than 10 that I have seen) where the Crucial memory and Hynix memory have not played well together. Since I don't have the Hynix memory on hand to test and it does not affect very many systems, I have no way to determine why in a few cases the two memory types have not worked well together.

    The problem could be almost anything and is impossible to determine based on the rarity of problems that have taken place. I can tell you is that our memory is fully compatible with the G5 and that in a few cases (I'm estimating less than .001% of our sales into the G5) our memory and the existing memory have not work well together. We have no way of knowing how our memory will work with the memory that ships with the computer you order, all I can say is that the odds are clearly in our! favor that our memory will work just fine in the system you purchase and with the memory that it ships with.
    -------------------

    My additional comments to everyone are: we have not been able to replicate this problem and that my identification of a Crucial/Hynix issue is based on what Joe provided us and what you see in his post above, it is not an accusation or implication of fault. With industry standards there are accepted tolerances that we, as manufacturers, must work within. In some cases you may have manufacturers with products that sit at opposite ends of the tolerance scales and that may cause problems when they are used together. This is true with all the components inside every computer manufactured. As a result in some cases certain combinations of hardware or specific circumstances cause inexplicable problems. There are just too many variables to determine the exact source of random problems such as Joe's.

    Brandon Guthrie
    Crucial Technology, Meridian Idaho

    View/reply at RE: Problems w/ Crucial RAM in G5 2.0 Rev. B
    http://discussions.info.apple.com/webx?13@@.6895ecb7/5
    Last edited by TZ; 02-24-2005 at 06:42 AM.

  10. #10
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    Default Memtest question

    I confess to having a rather unknown quality of RAM which came with the machine bought used, so I thought it might be useful to run this Memtest and/or Rember to see what's what.

    I haven't had time yet to run a full test with Rember, but it starts and progresses OK. The read-me with Memtest 4.04M states that more RAM can be tested than that available to test when running in Terminal, either by booting in Safe Boot and logging in as ">console" (which I can, but don't understand), or running Memtest in Single User Mode.

    If I use Rember in my User account, I can test 814MB of the installed 1024MB.

    If I run Memtest after Safe Boot, logged in as ">console", I can test 903MB. This is from the Memtest Read-Me; "By booting into Safe Mode, I've been able to test all but about 100M of the installed memory. You can add another 30M or so to the testable amount of memory by logging in as user ">console" without a password. This will drop you into console mode and turn off the window manager, freeing up the additional memory for testing. Now you should be able to test all except the approximately 70M of memory that OS X requires to run in this mode." I can only test all but 121MB using this method.

    If I boot normally and log in as ">console", I drop into the CLI, and shortly thereafter the screen goes clear blue and I have to hard restart to escape.

    If I boot in Single User Mode, the prompt is frozen, or freezes after entering 3 or 4 characters, and again I have to hard-restart to escape. I want to use the S.U.M. to try and test all but 2.3% of the installed RAM, which is about 1000MB.

    I guess my question really is about why I can't successfully boot in Single User Mode. There seems to be something rotten in the State of Denmark, and maybe I should have posted this in OS X General.
    "illegitimis non carborundum"

  11. #11
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    Lightbulb DFA result

    These are the DFA results:

    Model: PowerMac3,4
    PowerMac G4 (Digital Audio)
    DIMM0/J21
    DIMM configured for 512MB
    8008040D0A02400001755400800800018F04060101000E7054 0000140F142C40
    15081508000000000000000000000000000000000000000000 00000000001294
    00000000000000000000000000000000000000000000000000 00000000000000
    00000000000000000000000000000000000000000000000000 000000000064F5
    7.5ns PC133-233
    DIMM checks out OK

    DIMM1/J22
    DIMM configured for 256MB
    8008040D0A01400001755400820800010F04060101000E7554 00000F0E0F2A40
    15081508FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFFFF12F3
    C1494E46494E454F0836345633323330304755374420202020 20200332025108
    A3D12CFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFFFF64AF
    7.5ns PC133-222
    DIMM checks out OK

    DIMM2/J23
    DIMM configured for 256MB
    8008040C0A02400001755400000800018F04060101000EC090 0000140F142C20
    15081508000000000000000000000000000000000000000000 0000000000127F
    7F7FB5FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFF011E19
    9D6700FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFFFF64FF
    7.5ns PC133-333
    DIMM checks out OK

    DIMM3/J24
    DIMM not configured
    no DIMM present

    All your DIMMs checked out OK

    You've gotta love these machines! I don't have OS 9 installed so I ran DFA from the install CD and saved it as a Text Edit file in my Panther User Doc's folder, and voila! there it is in OS X. I knew I had this 222/223/333 mix, but it's all 7.5ns PC133 and didn't think it would be a problem, but maybe it is.

    I'll run DU from the install CD next and see what gives.

    Single User definitely hangs once the CLI screen has finished opening, sometimes the prompt is D.O.A. and sometimes I can enter a few characters before it freezes, but freeze it does.

    A hosed OS seems likely, and that's easy enough to fix, but it does beg the question "Why?"

    The other symptom which persists has to do with logging in as ">console".
    If I try that after a normal boot, the CLI goes to a clear blue screen shortly after appearing. If I try it in Safe Boot, it works OK. I just ran Memtest for 12 hours using that method. But...

    After running through 6 sequences with all OK results, testing 945MB of 1024, I quit and ran it again, and this time it locked down 950MB. So I quit and ran it again; this time it locked 970MB, but then went loopy with the constantly scrolling message "WARNING. No physical memory suitable for pageout or reclaim, pageout thread temporarily going to sleep."

    Seems like each time I run Memtest it grabs a bit more RAM until finally it goes unstable. Maybe that has more to do with Memtest than my machine.

    One other symptom, which may be unrelated, is that Help Viewer is hosed too, and not for the first time. In fact, it's hosed in my back-up too, so I've got a ground-up OS install coming anyway.

    biggles.
    Last edited by TZ; 02-21-2005 at 08:53 AM.
    "illegitimis non carborundum"

  12. #12
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    Default

    Dear Biggles,

    to me, your RAM seems fine. The Uni-North Memory Controller you have fitted inside your DA, is happy to handle CAS 3 RAM modules (PC133-3xx).
    The only thing I might want to suggest you is to move the DIMMs so as they show in this order:
    1. J21 - PC133-333
    2. J22 - PC133-233
    3. J23 - PC133-222

    And test your machine out.
    That should force the MC to set it's timing programming to suit the worst DIMM spec you have, for all the others too; but, as the other DIMMs bear better specs anyhow, they should take it easely.

    J24 is empty, right?

    IMHO, that memtest won't tell you much else that you already don't know about your DIMMs.

    If you want the full spec breack down, so as to compare it to your systems minimum requirements, while you are handling the DIMMs to shovel them around (if you want to do that), write down the small in-print you can read on those "little, black, bug-like" chips soldered on them, for each module (every DRAM device on each, single module should bear the same in-print).
    Then post that info here back for me to investigate.

    Your other arguments, about OSX stuff, are so very much interesting to me.... I am LEARNING (GREAT!!).

    Let me know.

    Ciao

    Costa

  13. #13
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    Lightbulb eMac DDR SDRAM

    Last edited by TZ; 10-08-2005 at 12:09 PM.

  14. #14
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    Lightbulb Rember "memtest" GUI

    A new bug fix/tweak of Rember was posted.

    Rember is a front-end GUI to the 'memtest' command line memory testing program. This will allow the user to select the number of test loops, as well as the amount of memory to test. There is a 'Log' tab that will allow the user to monitor memory testing. The user can toggle a 'verbose' switch to limit the amount of output. Allows user to quit Finder and other applications.

    ¥ Uses updated version (4.05M) of memtest executable
    - errors in memory testing are reported
    ¥ Rember reports errors (Rember source unmodified)

    http://www.kelleycomputing.net:16080/rember/
    Download

    MacIntouch -
    some memory problems are "data pattern sensitive" -- they only manifest themselves when a particular data pattern (or two) hits a particular cell (or two or three), and then maybe only after the DIMMs have been exercised (heated up) for a while. So, the triggering incident can be very rare and difficult to detect, but the result of a memory bug can spell disaster. Just one bit "flipped" to the wrong state in your INODE tree can trash your file system. Let alone a bit "flipped" when you do a firmware update or an OS update.

    If (you) find problems, then suspect the validity of all system installs and updates. In fact, all files written to any filesystem (or backup tape) created by his Dual 2.5 may well have problems.
    Don't test Apple Hardware Test (consumer or Apple version), and give memtest (4.05 just updated) http://www.memtestosx.org/ a go.

    ... read and heed the comments on AltiVec & stressing memory. While at Gary's site, pick up a copy of Timothy A. Seufert's Disk Test (Hard-Diskcorruption_test Folder.sit). http://www.gballard.net/macrant/ram.html

    http://www.macintouch.com/g5reader07.html#jan08
    Last edited by TZ; 02-24-2005 at 07:04 AM.

  15. #15
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    Default SpecTek - RAM vendor

    This post is actually a way to complete an answer for Biggles.

    In another thread, Biggles was asking me to find for him the specification data sheet for DRAM devices bearing the S80016LK7TW, which were soldered on a SDRAM module fitted inside his DA, returning him Latency values of 3-3-3.

    After some diggin' around, I came to the knowledge of another SDRAM vendor going by the name of SpecTek, which is a Company part of the Micron Technology, Inc. Group.

    From their web site, I have been able to retrive the very specification data sheet (".PDF" file download) for those DRAM devices, from which I am now able to confirm the following minimum details:
    • The part # S80016LK7TW has been substitued, since December 4th., 2004, into part # SAA16M8Y95AL4TW-75A.
    • The -75A items are PC133 compliant and, at that frequency, bear Latency values of 3-3-3.
    • The DRAM devices are built to 128Mbit density; it means that to make a 256MB SDRAM module, you need 16 of those, 8 on each side.
    • They are 3.3 Volts compliant and capable of an Auto Refresh sequence within 60 ns (3-3-3 + 1 clock cycle to the "ACTIVE" command period). The refresh sequence handles 4,000 RAM cell pages at a time. (This data is normal for a 133MHz compliant device).
    • The following is the new part # symbolism break-down:
      1. SAA = SpecTek Memory
      2. 16M8 = Configuration: 4 MBit RAM cell layers x 8 bit depth x 4 stacking layers (banks) = 32Mbit x 4 = 128Mbit.
      3. Yx5x = Design ID (it should be a physicall attribute, non-electrical)
      4. L4 = 3.3 Volt, Auto Refresh, 4K refresh (see above).
      5. TW = DRAMs built for a TSOP fitting, with 54-pins.
      6. -75A = PC133 (3-3-3) - See above.
    • They are compatible with Clock Cycle Timing of 7.5 ns
    • They are fully programmable and unbuffered.
    • They are Low Voltage TTL compatible, which is good for reliability and a typical characteristic of Micron based semiconductors.

    All in all, such DRAM devices are of a good, solid standard, though you should not pretend from them exceptional performance as from other Micron products.

    SpecTek is based at the Micron plant in Idaho and their Reliability testing takes place in burn-in ovens, a technology proprietary to Micron.

    This so as to be complete.
    Costa
    ________________________

    Ab ovo usque ad mala

  16. #16
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    Lightbulb B&W RAM specs demistified....

    Dear AdaMac,

    Quote Originally Posted by AdaMac
    It was the rerence to speed code that got me wondering about what ram I have now. I understand that 2-2-2 speed codes are to be used for maximum performance. Does DFA tell the speed code? to me it looks like I have 3-3-3, which is not listed in the apple article.
    The Latency values: 3-3-3 vs. 2-2-2, do NOT represent RAM speed code.
    They just represent a TIMING code the Memory Controller fitted on your motherboard *CAN* use with that particular SDRAM module.

    Let me do an example.
    The Latency value of a SDRAM module expresses the number of Memory Bus clock cycles it will take to complete a refresh sequence.
    As you know, Syncronous Dynamic RAM needs to be "refreshed" continuosly, otherwise it will loose quickly all "data" stored onto the RAM cells.
    SDRAM modules are made up by DRAM devices.
    DRAM devices are those little, black, bug-like chips soldered onto the green TSOP module, with 54 "legs", 27 on each side. It's inside those "little buggers" that the real technology resides.
    If you were to open-up one of those DRAM devices and you were to magnify it under a microscope, you would see a very dense and very thin array of semiconducting material, making up a "grill" looking very much like your square-sheet note pad.
    The crossing of every column with a row, represents a single RAM cell (or RAM address).
    Such "cells" can be charged (with SDRAM modules you use 3.3 volts on average), by the Memory Controller. If a cell is charged, when read it will return a binary "1" symbol. If it is not, then it will return a binary "0" symbol.
    A cell looses automatically it's charge after 60 ns (ns = nano seconds, or 1,000,000th of a second), if run on a bus clocking at 133MHz, and after 90ns, if run on a bus clocking at 100MHz.
    So, the refresh sequence is continuosly performed and consists in:
    1. Identifying each row and column (row address select, or RAS, and column address select, or CAS).
    2. Keeping track of the refresh sequence (counter).
    3. Reading and restoring the signal (or charge) from a cell (sense amplifier).
    4. Telling a cell whether it should take a charge or not (write enable).

    A Latency value of 3-3-3, means that the SDRAM module (at the frequency the value refers to) will take:
    1. 3 Memory Bus clock cycles to identify each column address select (CAS).
    2. During the above activity will ALSO keep track of the refresh sequence (counter).
    3. 3 Memory Bus clock cycles to "refresh" a charge on a cell (if it needs to) - (sense amplifier).
    4. 3 Memory Bus clock cycles to tell a cell, which has no charge, to take a new charge - (write enable).

    In your case, at 133MHz, as each clock cycle will take 7.5 ns to happen, the whole refresh sequence will last: (7.5ns x 3) + (7.5 ns x 3) + (7.5 ns x 3) = 67.5 ns. *BUT* the DRAM devices will return an ACTIVE READY signal to the memory controller after 60 ns. to "tell" they are ready for the next instruction.
    If you had a SDRAM module capable of a Latency value of, say, 2-2-2 at 133MHz, the whole refresh sequence would last 45 ns.
    You would thus save 22.5 ns each sequence. In any event, it's a time difference the human body cannot detect.

    The important thing about your RAM modules is that they can performe at 100MHz, as your B&W Memory Bus clocks at that frequency.
    You will find that your SDRAM modules are "backword" compatible to the PC100 specification (100MHz) and, also, that they can handle refresh sequences at 125MHz (i.e.: with 8ns intervals) if and when the Memory Controller needs it.
    BTW, it's the Memory Controller which is in charge of the Memory Bus frequency(ies).

    So, you need to look for SDRAM modules capable of running safely at 100MHz (PC100 - even if backward compatible from a PC133 standard), with a Latency value of 2-2-2 at 100MHz and capable of handling refresh sequences with 8ns. intervals.

    Post back if you don't understand.

    All the best.

    Costa

  17. #17
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    Lightbulb laptop RAM

    Quote Originally Posted by kaps
    ...I have two iBooks (G3/700 and a G3/600, both 12")....
    - How do I find out the other specs of the RAM? On the RAM itself, there is a sticker that says: 512M PC133 SDRAM; S/N 100790-0558....
    Your iBooks are either Late 2001 or Mid 2002 releases, or both. The main differences between the Late 2001 model and the Mid 2002 model are:
    • Graphic card - ATI Rage Mobility (2x AGP) vs ATI Mobility Radeon (2x AGP).
    • VRAM (Video RAM) - 8 MB vs. 16 MB
    • Optical Drive - Choice between CD-ROM, DVD-ROM, CD-RW or "Combo" CD-RW/DVD-ROM vs. "Combo" CD-RW/DVD-ROM, only.
    • Standard Hard disk: 15GB in size vs. 20 GB (though, the Late 2001 iBook, in the "Combo" optical drive configuration, sported a 20GB internal HDD, too).

    However, they both shared the same RAM SO-DIMM specifications; you should thus look for SO-DIMMs bearing the following minimum SDRAM devices specs:
    • PC100 or faster (provided they are backward compatible to the PC100 one; i.e., they can safely be runned at 100MHz frequency).
    • CAS Latency of 2 with an access timing of 7ns (ns = nanoseconds) or less.
    • Burst length must be at least of 4 pages (i.e.: when the internal Memory Controller is querying the SDRAM devices, these must show 4 pages of RAM addresses within the first memory bus clock cycle - a quite normal specification).
    • 3.3 volts compliant (it means that the Memory Controller will use such voltage to "write" onto the RAM address).
    • 256Mbits maximum density (it means that the maximum capacity SO-DIMM you can fit, is 512MB emplying 16 (S)DRAM devices - which are those small, black, bug-looking chips soldered on the SO-DIMM module - 8 on each side).

    If on your iBook/700 there is already implemented a SO-DIMM bearing better specifications than the two new ones you have purchased, it could be a possibility that the Memory Controller is unable to address them correctly, due to the fact that, upon boot, it reads the timing specifications from the SO-DIMM fitted in the first RAM expansion slot. As these are better than the ones you have installed in the 2nd slot, then it could be that the MC has difficulties in addressing RAM cells correctly on the other SO-DIMM, thus returning a "zero" reading.
    I don't know the iBook that well, but see if you can swap the SO-DIMMs around the 700MHz model.
    Quote Originally Posted by kaps
    ...- I didn't zap the PRAM yet. I'll give that a try. (The computer currently isn't in front of me.)

    - How do a do a open firmware reset?...
    Use these links to performe correctly the:
    • PRAM resetting, and
    • Open Firmware NVRAM reset. To access the Open Firmware mode, upon booting your iBook, keep depressed the < COMMAND > + < OPTION > + < O > + < F > keys simultaneously, until you get to a white screen with the flashing pointer and a typed message saying: "To continue booting, type 'mac-boot' and press return".


    PowerBooks/iBooks unresponsive after sleep
    RAM appears to be the culprit:

    "I have a PowerBook G4 15" 1.25Ghz and attempted to add house-brand RAM from CompUSA. I got two 512MB SODIMMs marked "PC-2100/2700." The RAM caused an initial crash on boot and then a kernel panic, but after that I was able to restart and use the new RAM fine, as long as I didn't put the machine to sleep.
    Kingston recommends PowerBook users turn off processor cycling ('highest performance' rather than 'automatic') for their RAM, and this seemed to help. With 'performance' on highest, I was able sleep the PowerBook and wake normally, but only if it had a power supply connected. If it was forced to run off battery power while asleep, it would not wake up.
    Apparently, for RAM to work in recent PowerBooks, it needs to support a low power sleep state. Most cheap/generic RAM brands don't do this, even though they claim PC2700 status and list the same specifications.
    Kingston, for example, has as least three different models of 'PC2700 SODIMM RAM,' all of which have the same specs but are designed for different models... a similar problem with 3rd party RAM in a 17" PowerBook using PC2100 RAM appeared to work, but always died in sleep.

    After biting the bullet and buying a Samsung 1 GB RAM SODIMM, I've had no problems with sleep."

    PC2700 DDR 200 pin SO-DIMM (backward compatible with PC2100)
    512 MB PC2700 DDR SO-DIMM 512DDR2700SO

    Upgrade for the Apple iBook (G4 1.2GHz)
    1GB ¥ DDR PC2100 ¥ CL=2.5 ¥ Unbuffered ¥ Non-parity
    ¥ DDR266 ¥ 2.5V ¥ 128Meg x 64

    http://www.apple.com/support/ibook/
    iBook Upgrades
    PDF Manual: Adding RAM Customer Installable Parts
    iBook Specification
    iBook Discussions
    ... Crucial's SO-DIMMs use Samsung chips. - Anandtech Mac Memory
    Last edited by TZ; 03-21-2005 at 05:36 AM.

  18. #18
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    Lightbulb DDR2, PCI-E revisited

    DDR2 memory tests, which we have performed earlier, showed that its higher latency is exactly the reason why it gets defeated by the regular DDR SDRAM. Many applications demand a high memory performance, and DDR2 SDRAM employed in LGA775 platform just couldn't provide it.

    DDR2 SDRAM can be faster. xbitlabs: DDR2
    DDR2 is actually poorly named. It should be called QDR, because the clock speed of the data bus is doubled, and it is triggered by both the rising and falling edges, which means it has four times the potential bandwidth of standard SDRAM devices.

    But the bandwidth improvements come at a cost to the latency.

    The best DDR1 memory has latency values of 2-2-2. But on the other hand, DDR1 uses these low latency figures at higher base clock rates, 200MHz for DDR1-400, opposed to 133MHz for DDR2-533, which means even equal latency numbers on the DDR2 RAM will result in worse latencies than DDR1, until the base clock speeds catch up. www.geek.com
    Last edited by TZ; 12-22-2004 at 07:17 AM.

  19. #19
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    Lightbulb DDR333/PC2700 in MDD

    Change in what Crucial uses in MDD.
    Apple MDD Expansion

    "... only the RAM with 16 chips--8 boxes on both sides -- did not stall the Apple Hardware Test CD. The RAM with 8 boxes was recognized by System Profiler, however, but caused innumerable panics, and seemingly unrelated problems."
    ------------
    The original OEM Micron RAM 256MB in MDD 1.25 has 8 chips on one side. The last time I bought RAM, it was the 16-chip with 8 on each side.
    -----------

    Crucial Ballistix Memory
    After much hair pulling and back-and-forth efforts, one of our members sadly discovered that Crucial Ballistix "Tracer" memory is not programmed to work in Macs, and never should have been listed as an option with any Mac models.
    ---------------

    DDR333 Spec for G4 MDD <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> There should also be no problem mixing and matching DDR 333 and DDR 266 DIMMs, but the bus on the 867MHz G4 is still 133MHz and the DDR 333 DDR SDRAM will simply act like a DDR 266.

    In either case, developers should take care to follow the JEDEC Standard No. 21 - C (Appendix D). In particular, make sure to program the Serial Presence Detect (SPD) EEPROM correctly. Byte 2 of the SPD should be a 07 (hex) to indicate DDR (for PC2700 / DDR333) and byte 9 should indicate 6ns or smaller clock cycle (1/6nS = 167MHz approx.).

    The only other thing to watch out for with DDR is to remember to specifically state ALL CAS Latencies and half CAS Latencies you support (in byte 19), since we can now have CAS Latencies like 2.5. Failure to follow the specifications and to add the supported CAS Latency would prevent the DIMM from being recognized.

    Apple Tech Note QA1191 <HR></BLOCKQUOTE>
    PowerMac G4 DDR-SDRAM
    Last edited by TZ; 02-24-2005 at 07:09 AM.

  20. #20
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    Lightbulb iMac G5: Memory specifications

    iMac G5 computers work with memory modules (DIMMs) that meet all of these criteria: PC3200, unbuffered, nonparity, 184-pin, 400Mhz DDR SDRAM.

    There are two RAM slots. The maximum amount of RAM you can install is 2 GB. You can use RAM module sizes of 256 MB, 512 MB and 1 GB, in either slot.

    Always follow the upgrade instructions for Memory and AirPort Extreme card installation as written. Never attempt to remove screws that are not listed in the upgrade instructions:
    iMac G5 RAM Upgrade

    Apple iMac G5 takes advantage of "interleaving" as mentioned in MacFixit

    iMac G5 128-bit mode RAM
    64 and 128 bits RAM on the iMac G5

    The 128 bits tests were conducted with two IDENTICAL 512MB sticks.
    If the results with 256MB and 1.25GB of RAM were of course identical (64 bits mode), in 128 bits mode, the throughoutput was on average 38% better.

    Those are indeed not performance gains one can experience on a day to day basis, but it is clear that using 2 identical RAM sticks will bring a noticeable performance boost nonetheless.

    We do put an emphasis on the term "identical", because Nicolas, another of our readers, tried with two 512MB RAM sticks from different anufacturers, and the iMac refused to switch to 128bits mode.

    the iMac G5 is even more picky about RAM than a Dual 2.5GHz PowerMac G5. Out of 6Kingston sticks, only one was accepted by the iMac G5.

    A tad more annoying, but to be confirmed, the iMac apparently has refused to switch 2 identical Micron RAM stick in 128bits mode.

    PPCNUX - Memory Performance Benchmark
    System Profile should show if they are working as one.
    I assume it enables DDR or 128-bit vs 64-bit.
    G5 test bus utility download

    DDR400
    MacGurus PC3200
    Last edited by TZ; 02-24-2005 at 07:07 AM.

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