Chapter 7: Computer Memory^147
Some of the video memory technologies in use are: Video RAM (VRAM) The most commonly used form of VRAM (“vee-ram”)
is also called video RAM (VRAM). VRAM is a dual-ported DRAM that acts as
a buffer between the CPU and the video display.
Windows RAM (WRAM) Although its name (it is normally referred to as
“Windows RAM,” not “wram”) suggests otherwise, this type of video memory
has nothing at all to do with the operating system with a similar name. Its name
comes from the fact that this type of video memory is accessed in blocks or
windows, which makes it slightly faster than VRAM. Windows RAM is a
high-performance video RAM that is better than standard VRAM for high-
resolution images.
Synchronous Graphics RAM (SGRAM) SGRAM (“ess-gee-ram”) is a
single-ported DRAM technology improved to run almost four times faster
than normal DRAM. It is a single-ported clock-synchronized video RAM that
uses specialized instructions to perform in a few instructions what would be
a series of instructions for other forms of VRAM.Parameter RAM
Macintosh computers store their internal configuration data, such as the system date and
time and other system parameters that must be stored between system boots, in what is
calledparameter RAM (PRAM). PRAM is the Macintosh computer equivalent of the PC’s
CMOS. In fact, the process called “zapping the pram” on a Macintosh is about the same
operation as removing the CMOS battery on a PC to reset its configuration parameters
back to their default values. See Chapter 6 for more information on PC CMOS.Logical Memory Configuration
Prior to Windows NT and Windows 2000, operating systems such as MS-DOS, PC-DOS,
orWindows3.xor9x,organizedthephysicalprimarymemoryintoalogicalorganization
that fit its processing needs. DOS and Windows operating systems define memory into
four basic divisions, as shown in Figure 7-7.Conventional Memory
Conventional memoryis the first 640KB of system memory (RAM). Two things came together
in the early days of PCs to fix its size to 640KB. The early processors could not address more
than 1MB of RAM and IBM reserved the upper 384KB of that space for its BIOS and utilities,
which left the lower 640KB for the operating system and programs. In use, conventional
memory usually contains the kernel of the operating system, user application programs,
routines that terminate-and-stay-resident (TSR), and system-level device drivers.