Vintage Computers

My collection of vintage computers follows a personal journey through computer technology and includes PDP-8, PDP-11, and Ohio Scientific machines. These machines represent various computer technologies spanning a little over a decade. The PDP-8/F, built in 1970, represents late 1960's technology (the original PDP-8 was from 1965 and utilized discrete transistors, this 8/F unit uses TTL chips). It is a classic "blinkenlight" machine and includes front-panel switches and core memory. The PDP-8/A is an updated, and less expensive, unit and was one of the last in the PDP-8 lineage. To me, personally, the PDP-8 represents a machine common in the 70's ... it was "technology that was". The PDP-11/34 was built with mid-1970's technology in which CPUs still consisted of discrete chips but now MOS and DRAM memories were available. Featuring an advanced architecture for it's day, the PDP-11 represents, for me, the machine I had always wanted while growing up ... it was the 1970's "dream machine"! Finally, the Ohio Scientific represents late 70's to early 80's microprocessor technology in which the CPU was a single chip (the 6502 in this case) and circuitry was greatly simplified over the PDP series where the CPU consisted of up to 100 chips on multiple separate boards. This was the machine I actually had and "cut me teeth" into computers with.

A Short History ...

The PDP series of computers were the pre-eminent minicomputers of the day, the PDP-8 often described like a Model-T. While the original PDP-8 machines used discrete transistors on many plug-in modules later PDP-8s like mine used medium-scale integrated circuits (primarily 14 and 16 pin chips).

PDP 8/S flip-flop Consider the flip-flop, an essential circuit in all digital computers. Early 1960's machines, including the PDP-5 (1963), and the PDP-8/S (1966) used flip-flop circuits built from discrete transistors. Components were arranged on modules - two flip-flops seen in the core memory circuit for a PDP 8/S, seen to the left, are actually housed on a single plug-in module, The Circuit for the R205 Flip-Flop Module seen here. This is how DEC entered the computer market with the pre-PDP LINC computer: DEC originally supplied simple transistor logic modules which some customers later arranged to form a simple computer. The idea demonstrated the need in the market for an inexpensive minicomputer which later became the PDP-5 in 1963 (at a cost of $27000). DEC's modules required a positive and negative power supply and logic levels were -3V for a logic '1', 0V for a logic '0'.

PDP 8/S R205 flip-flop A photo of the R205 Flip-Flop module (from PDP8.NET).

PDP 8/E flip-flop Beginning in 1968 DEC began using TTL (74xx series) integrated circuits in their modules which were then incorporated into PDP-8 minicomputers. By 1970 modules like the R205 gave way to larger boards containing many more, and higher density, logic chips. The same flip-flops used in earlier designs (which were composed of discrete transistors) were now replaced with integrated circuits. Where two flip-flops previously consumed an entire board (the R205 board above), they now fit on a single fourteen-pin IC, the 7474 dual flip-flop. Logic circuitry which previously occupied an entire rack of modules now fit on just three 10.5" by 9" boards in the PDP 8/E and 8/F processors (circa 1970 and 1972 respectively).

The PDP-8 was a twelve-bit machine and by the early 1970's DEC realized the need for a 'high end' sixteen-bit machine, the PDP-11. DEC retained the PDP-8 line introducing the PDP 8/A in 1974 - the line hence ran from 1965 with the introduction of the "straight eight" until the withdrawal of the 8/A in 1984 - an unheard-of twenty years! (Check out the PDP-8 FAQ for a complete breakdown of all PDP 8 models).

Early PDP-11's (circa 1971-72) used core memory while later units like my 11/34 (circa 1976) used MOS memory chips - the 11/34 represents a second-generation PDP-11 system while the updated, and more common, 11/34A represents a third-generation system (The 11/34 was actually ahead of it's time and most machines in 1976 still used core memory - the 11/34 had a core option as well). Like the 8's, early 11's used front-panel toggle switches and LED indicators to allow programming of bootstraps, etc. Later units used keypads and seven-segment displays and still newer PDP-11's yet had no front panel at all, opting for a serial connection to a terminal instead.

By the late 1970's, minicomputers gave way to microcomputers, and associated core memory gave way to semiconductor memory. Entire computers with memory fit on a single board. Even DEC began using micros developing a PDP-8 compatible microprocessor (the Harris 6100) and later PDP-11 compatible micros (the LSI-11's including the 11/03, 11/23, and 11/73). And while DEC's computers remained pricey, and inexpensive home computer market was developing. Many eight-bit micros were developed including the Motorola 6800, the inexpensive 6502, and the Zilog Z-80. By the mid-1980's these, too, were rendered obsolete with the introduction of the IBM-PC and clones sporting 16- and later 32-bit processors. My collection specifically targets my first real computer, the Ohio Scientific lineage. Ohio Scientific machines were relatively obscure in the days of micros with the Apple and Commodore machines being far more popular at the time.

And so, my collection spans several generations of machines which evolved as I grew-up, spanning from early 70's designs employing chips and core memory (the PDP 8/F) to primitive eight-bit microprocessor-based home systems (the Ohio Scientific). Each computer in the collection has its own page ... just click on the photos below for more details.

My Collection ...

DEC PDP 8/F PDP-8 Presenting two classic PDP-8's: an 8/F built during the early 1970's heyday of minicomputers and an 8/A, one of the last PDP-8 models built. Absolutely 'classic' machines, the PDP-8 was one of the first truly affordable minicomputers - the equivalent of the model T of the computer industry - and this lineage holds a prominent place in the history of computers.


DEC PDP 11/34 PDP-11 I have a PDP 11/34 (circa 1976, not the newer 11/34A). Originally, my system consisted of this CPU along with three RK-05 drives however the ravages of time (including fifteen years of storage in an unheated garage where mice made a home inside the drives and moisture and extremes of temperature destroyed mechanical components) resulted in complete destruction of the drives. The CPU was unharmed, though, and works quite well. This machine is serious 'heavy iron'. Another PDP-11 I have is a PDP-11/73A (LSI KDJ11-A CPU) with 8 MB RAM and an MFM Hard-Drive controller (Third Party: Dilog MQ606 Board) running RT-11XM v5.04. I also have a Q-niverter allowing interface between Q-Bus and Unibus system ... I plan on using this to allow my old PDP 11/34 to run RT-11 from a DEC RX02 eight-inch floppy drive.


My Ohio Scientific Page Ohio Scientific A page dedicated to my first real computer, an Ohio Scientific Superboard II which I got in 1979. A fantastic learning machine for me, this computer featured 8K of RAM and BASIC in ROM. I have a few superboards, and have collected a number of machines in the OSI lineage including several Challenger II machines (a 4P, and an 8P), and even a Challenger III machine featuring three CPU's (a 6502, 6800, and Z80) allowing the machine to run just about any O/S including CP/M.


A few cool links on vintage machines (in general) ...

Old Computers Dot Com a good overview of numerous old machines.

Apollo Guidance Computer Original documents and schematics including a description of a project to build a complete reproduction.