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کامپیوترهای قدیمی و امروزی

The IBM Personal Computer (“PC”) was not as powerful as many of the other personal computers it was competing against at the time of its release. The simplest configuration has only 16K on-board RAM and uses an audio cassette to load and save data – the floppy drive was optional, and a hard drive was not suported.

A basic system for home use attaches to an audio tape cassette player and a television set (that means no floppy drives or video monitor) sold for approximately $1,565. PC-DOS, the operating system, was not available on cassette, so this basic system is only capable of running the Microsoft BASIC programming language, which is built-in and included with every PC.

A more typical system for home or school with a memory of 64K bytes, a single diskette drive and its own display, was priced around $3,000.

An expanded system for business with color graphics, two diskette drives, and a printer cost about $4,500.

Five internal ISA expansion slots on the motherboard provide the ability to add additional memory and other capabllities, although one slot is usually occupied by the video card, and another by the optional floppy drive controller. A third slot typically has an RS-232 serial port card installed. A modem card for dialing-up remote computer systems became a popular option as well.

Although the original IBM 5150 “PC” supported only 64K of RAM memory on the motherboard, later versions used higher capacity memory chips, allowing up to 256K onboard – up to 640K with internal expansion cards.

The high quality (and very noisy) keyboard is the same as the IBM Datamaster, a business computer released earlier in the same year as the “PC”.

The 5150 “PC” wasn’t IBM’s first attempt at a compact, stand alone computer, although it is by far their most successful.
In 1975, the model 5100 was an entirely self-contained, portable computer system – probably the first ever.
Developed between 1979 and 1981, the Datamaster was an all-in-one desktop system for word processing.

These two earlier attempts were directed at engineering and high-end business, were very expensive and sold poorly.

For the “PC’, in order to save time and money, instead of developing their own hardware and software, IBM used already available off-the-shelf components. The CPU was from Intel, and the operating system (OS) was by Microsoft, who licensed it to IBM as PC-DOS.

Other companies could in theory obtain these same components and create their own version of the PC, and cut into IBM’s market. But there was one aspect of the PC which could not be legally copied – the BIOS, as it was copyrighted and protected by law. But Compaq and the others eventually found a legal but ‘dishonest’ way to duplicated that as well, opening the floodgates to cheaper but still compatible IBM clones.

Actually, there is a bug in Microsoft’s floating-point math routine of the PC’s BASIC ROM chip. If you ask the system to divide 0.01 by 10, it displays 9.999999E-4, instead of the correct answer of 0.001.

Although not necessarily the best machine by technological standards, IBM’s expertise and the fact that the IBM PC actually looks and feels like a professional computer system made the IBM PC and subsequent PC clones extremely popular. They have evolved into today’s so-called Wintel (Windows + Intel) computer systems, used world-wide.

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