THE PDP-8 AND OTHER 12-BIT COMPUTERS 197
while not increasing price significantly over that of a slower speed design. Th cost per word was modestly higher with the PDP-8 than with the PDP-5, but the PDP-8 had 6 times the performance of PDP-5. Thus, the PDP-8 crosses three lines of constant price/performance in Figure 26.
2. The PDP-8/S was an attempt to achieve a minimum price by using serial logic and a minimum price memory design. However, the performance of the PDP-8/S was slow.
3. The market pressures created by PDP -8/S performance probably caused the return to the PDP-8 design, but in an integrated circuit implementation, the PDP-8/I.
4. The PDP-8/L was relatively expensive, so the PDP-8/L was quickly introduced to reduce cost and bring the design into line with market needs and expectations.
5. The PDP-8/E was introduced as a high performance machine that would permit the building of systems larger than those possible with the PDP-8/L.
6. The PDP-8/M was a lower cost, smaller cabinet version of the PDP-8/E and was intended to meet the needs of the OEM market.
The design goal of machines subsequent to the PDP-8/M has been primarily one of price reduction. The PDP-8/A was introduced to further reduce cost from the level of the PDP-8/E and PDP-8/M, although some large system configurations are still built with PDP-8/E machines. The CMOS-8 chips represent a substantial cost reduction but also a substantial performance reduction. The CMOS-8 performance is one-third that of a PDP-8/A, so a stand-alone system using a CMOS-8 is less cost-effective than an PDP-8/A when the central processor is used as the only performance criterion.
(c) CMOS-8 (6100) processor-on-a-chip family.
(d) VT78 computer-in-a-terminal.
Figure 28. Evolution of PDP-8 Family PMS structures.
The main reason for using large-scale integration is the reduced cost and smaller package rather than performance. Obviously, the next step is increased performance or more memory, or both more performance and more memory on the same chip.