Low latency 70ns 512kB 68-pin VRAM SIMM for Apple Macintosh computersDesigned by Siliconinsider in France
Get ready for more coming colors in the air thanks to this piece of a newly made 512kB 68-pin VRAM memory module manufactured by myself! The memory modules have been engineered using high quality 4 l…Read More…
Get ready for more coming colors in the air thanks to this piece of a newly made 512kB 68-pin VRAM memory module manufactured by myself! The memory modules have been engineered using high quality 4 layer gold plated printed circuit board with internal power and ground planes for maximum data integrity and low power supply ripple. Each memory modules has been professionally hand assembled using new old stock memory chips, and has been individual tested in a vintage Macintosh machine (LC475).
Is this memory compatible with my Macintosh? 68-pin VRAM are used in many 68k-era macintosh, as well as on the original PowerBook Duo Dock, some NUBUS video cards and early Power Macintosh PDS video card. Some Macintosh do not have integrated video, or use the main RAM as video memory, and do not use 68-pin VRAM SIMM. Please check the compatibility list below (as well as in the listing images) to see if your Macintosh model will support these SIMMs (marked 512k in dark purple).
What will I gain by adding VRAM to my computer? Additional VRAM will bring more color modes and higher display resolution modes. As a rule of thumb, the amount of color and resolutions is given in the table below (as well as in the listing images). Not all machines can display all color modes and all resolutions because of possible hardware limitation on certain machines. I encourage consulting the Apple Service Pages which will list all the available color modes and resolutions that can be achieved by your particular machine, depending on the amount of VRAM installed.
Does my computer support 256k SIMM or 512k SIMM? Both will work in all supported computers, however some models will not benefit from 512k modules as they will only treat them as 256k modules. Check the compatibility list to see if you would benefit from 512k modules. Some models necessitate adding VRAM SIMMs in pair.
What is memory latency, and what is appropriate for my computer? Latency is the amount of time between a memory request (read or write), and the moment the data is propagated through the memory circuitry and being made available to the system. The memory controller of most 68k macs is designed to include wait-states to satisfy memory with 100ns latency. Only recent Macintosh models, like the latest Quadras and the Power Macintosh 6100/7100/8100 PDS card are designed to use 80ns modules. Check the compatibility list to see if your machine requires 100ns or 80ns latency.
Will my computer run faster or the video be more responsive with a VRAM module with lower latency? No, because the system is unaware of the latency of the memory. The memory controller is pre-programmed with the appropriate wait states depending on the stock speed of the system bus. The system will run fine but without added benefit.
I have overclocked my computer, will this affect anything? Yes, because the memory controller is clocked on the system bus, the pre-programmed memory access wait-states will also be shortened. If the machine is overclocked, 100ns modules will not be adequate, and 80, 70 or 60ns modules may be needed in order to keep up with the faster memory access rate. Specific memory chips are tested in factory and binned in different latency grades according to their measured performance. The latency grade include a guaranteed operation margin, such as a 80ns rated chip may have an actual latency of 72ns.
What will happen if the latency is too great relative to the overclock? The memory will not be able to sustain the data rate and graphic glitches will appear on the screen. If the memory is run at the limit of the specifications, glitches can start to appear with changes in the physical environment inside the computer, such as when temperature increase, because latency is temperature dependent.
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Wilfried | Dec. 4, 2023
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