The IBM PC was released on August 12, 1981.  The machine is model 5150 and the monochrome monitor is model 5151. The desktop design is rather common in the CRT era as monitors were generally placed on top the machine. We bought one of the IBM PC machines in 2001 as the machine was much more capable..The motherboard supports 256KB which is 4 time more than any CP/M machine can handle.


  • Intel 8088 4.77 MHz
  • OEM motherboard
  • 16KB-64KB FP DRAM 256KB maximum
  • 5¼” full height floppy 160 KB
  • 63W PSU
  • 83-key keyboard
  • IBM DOS 1.0


The IBM PC came with the Intel 8088 CPU that ran at 4.77 MHz. There was a socket for the optional 8087 floating point processor but it was so expensive that few were ever purchased. The machine came with 16KB-64KB of memory. ISA cards with a real time clock, a parallel port and additional memory were popular expansions. Most machines eventually were upgraded to 640KB using add-in cards to maximize DOS memory so that Lotus 1-2-3 could work with larger worksheets etc.

Later revisions came with as much as 256KB of RAM but a BIOS bug made the machine underutilize the actual amount of memory present. Eventually IBM provided a new BIOS chip so that the machine would work properly.

IBM PC 5150 motherboard

The machine came with a dust cover that fitted over the floppy drive bay. This was unusual as no other machine every came with such a component before or subsequent.

The machine came with 8 slots for peripherals. The machine did not even have built-in ports outside the keyboard and a port for a cassette recorder.

The keyboard was very heavy and it was designed to for users of the old Selectric typewriters. Depending on the software the function keys could be used for several purposes. In practice software from CP/M was ported to the PC and most of that used the CTRL keys for functions.

Most machines used 3 or 4 slots for peripherals. Serial ports, parallel ports and many other types of 8-bit cards quickly came to market. Most machines of this class all used a longer card with additional memory, a real-time clock and a parallel port. The aftermarket support really make the PC the goto platform.


We installed a full length 3COM 3C501 network card but we replaced it with a smaller models until finally 10BASE-T became available. Machines were widely connected into local area networks using Novell Netware.

The machine we had came with a single floppy drive but we installed a second drive to make copies of disks easier. Some machines used a cassette drive for storage but the majority of business users bought machines with a floppy disk drive.

The machine’s BIOS was 8KB but the remaining 56KB of address space was filled with a BASIC interpreter. It was launched by using BASICA from a PC DOS floppy.


Eventually we installed a 30MB hard disk that was from a junked Control Data mainframe. This gave the machine a big boost in usefulness. We had already installed a better rated power supppy.

The hard disk was full height which fit beside the floppy drive easily. 5¼” half height disks did not become readily available fora couple of years. With half-height disks it is possible to install 2 hard disks.

The WD controller card we used was 1:1 which made the disk relatively fast. Many early disk controllers needed as many as 5 revolutions to read all of the sectors which made them rather slow.

DOS programs tended to be small so many hundreds of programs can fit on the 30MB disk along with all of the data files imaginable.

Most users used floppy disks, hard disks were far too expensive for use for many years to come. Hard disks started at $1000 in 1981.


IBM offered a few video cards for the PC. It was possible to use more than one video card simultaneously. This capability has been a hallmark of the versatility of the PC from the start.


The monochrome display adapter was the lowest cost card but it could display 80×25 characters on the monitor. Most machines at the time we less. The card was 13″ long and loaded with chips.

Hercules came to the market with a card that was compatible but it could operate in bitmap mode to provide high resolution graphics. The Hercules card was extremely popular with PC users for a long time.

The Hercules card was also much shorter than the original MDA card so it used a lot less power making it very popular with users. The Hercules card also provided a parallel printer port which made it easy to attach a printer.


The color graphics adapter was cable of being display on a television with a RF modulator. It had an RCA plug that could also used with a video recorder.


Games on the IBM PC were limited to simple graphics. Centipede was ported from the coin-op arcades and many others soon followed.

Centipede was a good example of bad game design. The PC had a counter timer chip but the developer used a simple NOP loop for timing. When the IBM AT came to market this game run very fast and it became unplayable.

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