Old Computer Confiregation

The VT78 system, also called DECstation or DECstation 78, is based on the Intersil/Harris 6100 microprocessor and is packaged in a VT52 case. The 6100 processor was able to run at 4 MHz, but in the VT78, it was only clocked at 2.2 MHz because of the speed of the DRAM used and the deliberate use of graded out chips.

Using TTL MSI and LSI components, DEC could pack a system into the vacant space in a standard terminal case, allowing PDP-8 systems to compete with personal computers in the small business and office automation market. This was a natural follow-on to the desk-mounted workstation configurations in which the PDP-8/A was already being sold.

Apart from some minor details, it is fully PDP-8/E compatable, even at the level of I/O instructions for the standard periperals; this was the last PDP-8 to offer this level of compatability.

It was not possible to continue from a halt without restarting the machine. In addition, none of the peripherals available on this machine needed DMA (data break) transfers.

The VT78 was sold with 16k words of DRAM with the keyboard and display of the VT52 terminal. An RX01 dual 8" diskette drive was included, packaged in a teacart pedestal under the terminal. The console (device 03/04) and the serial ports (devices 30/31 and 32/33) are compatible with the M8650 KL8E, with the latter extended to allow software controlled baud rate selection. There are two parallel ports; device 66 (compatible with the M8365 printer controller) and device 47, compatible with the nonstandard port on the M8316 DKC8AA. There is also a 100Hz clock compatible with the clock on the M8316 DKC8AA.

The standard ROM boots the system from the RX01 after setting the baud rates to match that selected by the switches on the bottom of the VT52 case.

This was a closed system, with few options. The base configuration was able to support two RX01 drives (later RX02), for a total of 4 transports. Various boot ROM's were available, including a paper-tape RIM loader ROM for loading diagnostics from tape. Another ROM boots the system from a PDP-11 server in the client/server configuration used by WPS-11.
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The V778 came with a FORTRAN, a BASIC compilers, the PAL-8 assembler and various other utilities.

The standard DECstation configuration, which includes the VT78 (video terminal, mainboard, memory, real time clock and floppy drive interface) and a dual floppy disk was priced at $7995.