Part of the boot process involves copying some of the BIOS instructions from ROM up to RAM and then executing those instructions from RAM rather than from the ROM chip. Why? Because ROM is much slower than RAM, performance speed increases when executing the instructions from RAM instead of from ROM. The process in which a copy of the BIOS instructions is shadowed, or copied, to an area of memory called shadow RAM is called shadowing.
Video RAM (VRAM) is dual-ported memory, meaning it can be read from and written to at the same time. DRAM is single-ported, which means that the memory can be written to and read from, but not simultaneously - only one direction at a time. VRAM, however, lets you do both simultaneously.
VRAM is most commonly used on video accelerator cards to store the values of the pixels on the screen for refresh purposes. VRAM is the favored memory for video because it outperforms the other memory types by being dual ported.
Window RAM (WRAM), also known as Window Accelerator Card RAM, is a modification of VRAM and is also used for video display purposes. Like VRAM, WRAM is dual-ported memory but runs about 25 percent faster. In general, WRAM offers better performance than VRAM.
In this tutorial:
- Understand Memory
- Understanding the Types of Memory
- Read-Only Memory (ROM)
- Random Access Memory (RAM)
- CMOS RAM
- Shadow RAM
- Identifying the Types of DRAM
- Extended data output
- Rambus DRAM
- Memory Packages
- Understanding Error-Checking Memory
- Working with Cache Memory
- Installing or Upgrading Memory
- Installing memory on desktop PCs