lec5- Architecture

Architecture

In addition to their rated Mega Hertz (MHz) speed, and the amount and type of cache, processors can be categorized by their internal structure, or architecture; it basically determines the language software programs must use to work with them. The vast majority of IBM-compatible PCs use what are called x86 processors because they are derived from Intel’s 8086 processor — the same processor found in some of the earliest IBM PCs. The very first IBM PC, however, used Intel’s 8088 processor, a predecessor to the 8086.
The 8086 and 8088 are often confused because the later chip used a lower number as its product name. The reason for this is that the 8088 was an 8-bit processor, while the 8086 is a 16-bit processor and hence the difference in the last digit.
The x86 family of processors share a common set of instructions that software programs use to run on the chip. These instructions are the basic "language" of the processor and determine what types of calculations the processor is capable of doing.
Faking it with software
When is an x86-compatible processor not really an x86-compatible processor? When it’s a Motorola processor (or one of several other types) pretending to be an x86-compatible via trickery, commonly called software emulation. Software emulation basically fools an application into thinking it’s running on the type of chip that the application was originally written, even though it really isn’t. The processor does this by translating one set of instructions to another. So, for example, Insignia Solution’s SoftWindows 98 or Connectix Corp.’s Virtual PC, which are programs for the Apple Macintosh, enable Mac users to run Windows programs on the Motorola processor inside the Macintosh, even though those Windows programs were written for Intel processors. Basically, the instructions the Windows program (and even Windows itself) calls for are translated into a form that the Motorola processor understands through the software emulation program. Then the Motorola processor performs the necessary calculations, and finally, the software emulator takes those results and feeds them back to the Windows application. As far as the application is concerned, it’s running under Windows on an Intel processor, as normal. Performing these translations back and forth takes time and processing power, however, and software emulators are much slower than running the same programs on PC hardware.