(^148) PC Hardware: A Beginner’s Guide
The Upper Memory Area
Theupper memory areawas originally designated by IBM for use by the system BIOS and
video RAM, the 384KB that remains in the first 1MB of RAM after conventional memory.
As the need for more than the 640KB available grew, this area was designated asexpanded
memoryand special device drivers were developed, such as EMM386.EXE, to facilitate its
general use. The use of this area frees u ps pace in conventional memory by relocating
device drivers and TSR programs into unused space in the upper memory area.Extended Memory and the High Memory Area
All of a PC’s memory beyond the first 1MB of RAM is calledextended memory. Every PC
hasalimitofhowmuchtotalmemoryitcansupport.Thelimitisinducedbyacombination
of the processor, motherboard, and operating system. The width of the data and address
bus is usually the basis of the limit of how much memory the PC can address. The
memory maximum usually ranges from 16MB to 4GB, with some newer PCs now able
to accept and process even more RAM. Regardless of the amount of RAM a PC can support,
anything above 1MB is extended memory.Figure 7-7. The DOS/Windows logical memory layout