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The high-density SDRAM device is a higher-performance, lower-cost replacement for either four 4-Mbit Extended Data Output (EDO) memories, the most dominant type of memories used today in PC graphics subsystems, or two 8-Mbit Synchronous Graphics RAM (SGRAM) devices.
"We expect 16-Mbit SDRAM memory to become the technology of choice for graphics subsystems because it provides an easy way for vendors to reduce the cost of their PC graphics boards and to simplify their designs," said Anthony Balistreri, manager of TI's Graphics Memory Development. "In the case of 4-Mbit EDO memories, four chips can be replaced with one 16-Mbit device and the performance will increase by approximately 20 percent. With 8-Mbit SGRAMs, costs will be lowered by reducing the number of components and, in addition, SGRAMs are more expensive because they have integrated circuitry for features that aren't needed by mainstream PCs. Since 16-Mbit SDRAMs are drop-in replacements for 8-Mbit SGRAMs, a major re-design effort is not needed either."
As synchronous memories, the 16-Mbit devices are synchronized to the system's clock to simplify design and enhance their use with high-speed microprocessors and controllers. For example, with a system clock speed of 125 MHz, two 16-Mbit SDRAMs can provide graphics data at a rate of one gigabyte per second (GB/s) over the typical PC's 64-bit graphics bus. The
new devices are particularly well suited to systems with speeds
in the range of 100 to 133 MHz. Because of their high bandwidth,
the 16-Mbit SDRAMs are appropriate for other applications as well,
such as set-top boxes for cable television, palm-top computers,
personal digital assistants (PDAs), inexpensive network computers,
video game consoles and video conferencing systems.
To provide the most cost-effective graphics solution for mainstream PC applications, the TI 16-Mbit devices do not include features that are used only by specialized applications. For example, the "block write" capability of SGRAM memories is only marginally useful for high-end three-dimensional (3D) applications where it can increase 3D performance by approximately 2.5 percent. Integrating the block write feature into SGRAM memories adds cost to the devices by expanding the required silicon by as much as five percent. The additional circuitry required for block writes can also limit the overall speed of the memories.
"The 32-bit width of a SDRAM device will provide the bandwidth needed by mainstream PC applications," said Balestreri. "Some of the extra graphics features that are built into SGRAM have driven up the cost, but they don't add any real value for the majority of PC users. Since the 16-Mbit devices have the same package and pinout as 8-Mbit SGRAM, replacing SGRAMs does not involve any major re-design of the boards. TI's 16-Mbit SDRAM can offer the benefits of reduced costs, less board space and similar performance in the majority of end-user applications."
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