Computer History Of The World, Part 4

by Bob Seidel

And now for our next installment of computer history.

When I joined IBM in the late 60's, I worked at Kingston, NY. Kingston and Poughkeepsie (about 26 miles to the south) were the home of all the large mainframe development in IBM. Let's look at what mainframe computers were made of in those days, and how they would compare to computers today.

Mainframe computers were basically all that there was at that time. There was no such thing as a PC or home computer, and the smaller boxes called minicomputers were still a few years off. Mainframes were boxes as big or bigger than refrigerators, and usually there were a number of these boxes all tied together with massive cables to make up one computer system.

IBM had recently introduced a computer product line called System/360. 360 (as it was known) was a series of computers ranging from a low end mainframe that was basically a single box, to high end models that required huge rooms. The primary selling point of 360 was that even though the computers were physically quite different throughout the product line, they all worked and behaved the same. Thus, programming written for one computer model would work on them all. The only difference was speed and storage capacity.

The 360's were all transistorized (although IBM was still selling some tube equipment), but there was no such thing as an integrated circuit yet.

The 360 model that I am most familiar with was the model 70. The 360/70 was very large and expensive, and was really only developed for NASA to use in early manned space launches. The main processing unit was housed in a wall that was about 20 feet long, 3 feet wide, and about 7 feet tall. Along the front side of the wall was a light display of about 2,000 bulbs - all used to show the status of the computer. Two operator terminals (looking like large IBM Selectric typewriters) extended from the front.

Along the back were up to four memory cabinets, sticking out the rear. These cabinets held the RAM of the computer - and each cabinet held 256KB. Note: I said KB (kilobytes), not megabytes. These cabinets were about six feet long, and as wide and high as the other boxes.

Cooling was by forced air from below. The computers were installed on very heavy tiles that were raised up above the floor of the room. The raised tile area contained the cooling air and also the cables. Later IBM mainframes used chilled water cooling piped right into the computer.

Now, this was just the CPU and RAM - the equivalent of that today would be the Pentium chip and 2 or 3 memory DIMM modules on your PC today. In order to run its I/O gear (disks, tape drives, etc.) the 360/70 required more external boxes called Channels.

The I/O (input/output) gear consisted of a card reader and punch (we used punched cards in those days), two model 1403 printers (each bigger than a refrigerator) and eight tape drives. The tape drives were units about three feet wide and six feet high. Four of those also had a refrigerator-sized box to control them. The disk drives were about the size of washing machines.

Computed to today's PC, this huge pile of hardware was very slow. The CPU ran at 1 MHz. (one megahertz). Today's Pentiums run at almost 2 GHz. (gigahertz), or about two thousand times faster. The average PC today has 128MB of RAM - the 360/70 had 1MB of RAM. The disk drives held 7MB of data - about five of today's floppy disks. Hard drives today hold up to 100GB of data and run much faster.

So, things have really changed in computer hardware! Next time, we'll go into the software that was used.

(Bob Seidel is a local computer consultant in the Southport / Oak Island area. You can visit his website at or e-mail him at