Introduction to the IBM PC/XT :

The original IBM Personal Computer was released in August 1981. It cost a little under $3000 and came with 64Kb of Random Access Memory (RAM), 40Kb of Read Only Memory (ROM) which included a BASIC interpreter, a 160Kb floppy disk, version 1.0 of MS-DOS, and a cassette interface.

In March 1983, the IBM Personal Computer XT (eXtended Technology) was introduced. It included more memory, support for a Hard Disk, more expansion slots, and a newer version of MS-DOS (version 2.0). Since then, the PC has dominated the home and office market and the number of PC's in the world today is measured in hundreds of millions.

The architecture of the IBM PC/XT is quite simple by today's standards. It consists of a Central Processing Unit (CPU) which is an Intel 8088 running at 4.77 Mhz, some RAM, some ROM containing the machine's Basic Input Output System (BIOS), and a number of support chips to handle various peripheral devices. In order to execute PC-compatible programs a computer's CPU, BIOS and support chips need to provide similar functions to those provided with the IBM PC/XT.

All PC-compatible computers (even a 3Ghz Pentium IV) are equipped with hardware to provide this backward compatibility and are therefore able to execute the large number of applications which have been developed for PC-compatible computers in the last 20 years.

Introduction to the Microsoft H/PC and P/PC :

The Handheld Personal Computer (H/PC) and Palm-sized or Pocket Personal Computer (P/PC) are new categories of mobile devices built around the Windows CE operating system to bring Windows to the palm of your hand. More than a personal digital assistant, the H/PC or P/PC is a fully featured computer with a miniature footprint. Formerly know by the code name "Pegasus", Windows CE is an entirely new compact and portable operating system built from the ground up to be appropriate for a broad range of business and consumer devices.

The architecture of the H/PC or P/PC is not rigidly defined, and an H/PC or P/PC manufacturer can alter any of the hardware parameters as long as they provide appropriate Windows CE drivers for the modified hardware. In addition, the CPU can be one of several types and does not have to be Intel x86 compatible. In fact, current H/PC's and P/PC's only use Hitachi SH, MIPS and ARM-compatible RISC processors, none of which are Intel x86 compatible.

Microsoft has designed the Windows CE operating system so that existing applications for desktop versions of the Windows operating system can be relatively easily modified and re-built for the H/PC or P/PC. However, a large amount of PC-compatible applications are not designed for desktop versions of the Windows operating system and are unlikely to be rewritten for the Windows CE operating system.

Introduction to PC emulation :

Imagine you have an executable PC program that you wish to run on another computer (for example, a Windows CE H/PC or P/PC). If you try to run this program on the H/PC or P/PC, it will not work for the following reasons:

• Different operating system: PC-compatibles run an operating system known as the Microsoft Disk Operating System (MS-DOS or DOS for short). H/PC's and P/PC's run Wndows CE which is incompatible with MS-DOS.
• Different processors: The processor in the H/PC or P/PC is unlikely to be an Intel x86 compatible chip and hence will not be able to understand the machine code instructions contained in the executable program.
• Different machine architectures: The H/PC or P/PC has a totally different machine architecture. That is to say, the memory will be laid out differently, the peripherals will be different - both in the chips used to control them, and the addresses and commands they respond to.

Introduction to PocketDOS :

PocketDOS is based on XT-CE, an IBM PC/XT emulator for Windows CE which emulates a PC with an 80186 processor, 1Mb of RAM, a (S)VGA-compatible display and the standard support chips. This allows most applications designed for PC-compatible computers running MS-DOS to run on the pocket computer. PocketDOS does not emulate DOS (or any other operating system), but is included with evaluation versions of Datalight ROM-DOS 6.22, Caldera DR-DOS 7.03 and FreeDOS. In conjunction with running a 'real' DOS, PocketDOS is able to provide the same level of application compatibility as the original IBM PC/XT, while still allowing the pocket computer user access to all of the features and applications it's native operating system. In addition, PocketDOS is also able to run many other operating systems designed for the IBM PC/XT computer.