Page 12 - DCAP103_Principle of operating system

Unit 1: Operating System

1.1.4 Other Systems Notes
Mainframe operating systems, such as IBM’s z/OS, and embedded operating systems such as
VxWorks, eCos, and Palm OS, are usually unrelated to Unix and Windows, except for Windows
CE, Windows NT Embedded 4.0 and Windows XP Embedded which are descendants of Windows,
and several *BSDs, and Linux distributions tailored for embedded systems. OpenVMS from
Hewlett-Packard (formerly DEC) is still under active development. Older operating systems which
are still used in niche markets include the Windows like OS/2 from IBM; Mac OS, the non-Unix
precursor to Apple’s Mac OS X; BeOS; RISC OS; and AmigaOS. Research and development of
new operating systems continues. GNU Hurd is designed to be backwards compatible with
Unix, but with enhanced functionality and a microkernel architecture. Microsoft Singularity is
a research project to develop an operating system with better memory protection.

1.2 History of Personal Computers

A personal computer (PC) is usually a microcomputer whose price, size, and capabilities make
it suitable for personal usage. The term was popularized by IBM marketing.

Figure 1.1: Personal Computer

Time share “terminals” to central computers were sometimes used before the advent of the
PC. (A smart terminal — televideo ASCII character mode terminal made around 1982.) Before
their advent in the late 1970s to the early 1980s, the only computers one might have used if one
were privileged were “computer-terminal based” architectures owned by large institutions.
In these, the technology was called “computer time share systems”, and used minicomputers
and main-frame computers. These central computer systems frequently required large rooms
— roughly, a handball-court-sized room could hold two to three small minicomputers and its
associated peripherals, each housed in cabinets much the size of three refrigerators side by side
(with blinking lights and tape drives). In that era, mainframe computers occupied whole floors;
a big hard disk was a mere 10–20 megabytes mounted on a cabinet the size of a small chest-type
freezer. Earlier PCs were generally called desktop computers, and the slower Pentium-based

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