Uploaded October 2025 | Updated September 2026, 2 weeks ago
In this month's episode of State of Electronics, we take a look at Sydney University’s KDF9. Made by English Electric, it was delivered to the institution in 1963. The KDF9 was a fast, transistorised, parallel processing machine. It was designed with Australian computer pioneer and philosopher Charles Hamblin’s “stack approach” incorporated. Hamblin had presented his idea of “Reverse Polish Notation” and the stack concept at the 1957, 2nd Computing Conference, held at WRE in South Australia, where engineers from English Electric, who were in attendance, took those ideas and built them into the KDF9. This resulted in a very fast machine for its day. The KDF9 had been purchased as a replacement for SILLIAC; however, SILLIAC continued on for a while longer as part of the Sydney University cluster of computers at the Basser Computer Laboratory, where it was connected to the KDF9 and several other computers, creating one of the first Local Area Networks. The KDF9 was used to create mathematical plots and was among the first computers in Australia to develop Computer Graphics. The KDF9 was decommissioned in 1968.
Some Technical details:
The design of the KDF9 was based on the concept for an address-less programming language designed by Charles Hamblin called “GEORGE”, where arithmetic operations were carried out on values in a stack. The KDF9 had two stacks: one for values and the other for return addresses when subroutines were called. Both stacks had 16 words. This design reduced the size of instructions to as little as one unit of 8 bits. This had three advantages: Integer addition and subtraction took 1 microsecond; it reduced the data traffic between the processor and the memory; and compilation of programs took less time. The latter had the fortunate outcome of using Reverse Polish Notation. Translation of an algebraic expression to Reverse Polish Notation inherently produced a sequence of names and operators that was in perfect order for producing the corresponding machine instructions: names corresponded to an instruction to fetch from memory, while operators corresponded to an instruction to carry out the required arithmetic operation. Having values in a stack made it convenient to duplicate the top of the stack and to rearrange some values in the stack, including swapping the top two values. These operations were fast. Multiplication and division, whether integer or floating-point, were also quick. Multiplication took 14 to 18 microseconds, and division took 30 to 35 microseconds. Shifts took from 1 to 4 microseconds.
With a 48-bit word, the KDF9 could handle half-length and double-length values.
Solving 100 simultaneous equations took 15 seconds on KDF9, the program occupying only 36 words. SILLIAC's L2 equivalent took 4 minutes, including input-output, with a maximum of 39 equations.
At 1000 characters per second, the KDF9 paper tape reader was four times faster than SILLIAC, and the paper tape punch was twice as fast. Input-output devices had their own controllers.
"Worth a Thousand Words" by F.M. Larkin 1967 used with permission from Graham Larkin. To see the original film, visit: youtube.com/watch?v=JaHqzQtaVmM&t=677s
State of Electronics is working hard to bring this series to you, but we need your help. Acquiring and licensing images and filmed footage is both time-consuming and expensive. We have set up a GoFundMe campaign to help with this process. You can greatly assist us by donating here: gofund.me/be05614f
Please note: No Ai training is allowed on this channel. Do not replicate any part of this film in part or whole.
You are free to link back to this uploaded video on YouTube.
In this month's episode of State of Electronics, we take a look at Sydney University’s KDF9. Made by English Electric, it was delivered to the institution in 1963. The KDF9 was a fast, transistorised, parallel processing machine. It was designed with Australian computer pioneer and philosopher Charles Hamblin’s “stack approach” incorporated. Hamblin had presented his idea of “Reverse Polish Notation” and the stack concept at the 1957, 2nd Computing Conference, held at WRE in South Australia, where engineers from English Electric, who were in attendance, took those ideas and built them into the KDF9. This resulted in a very fast machine for its day. The KDF9 had been purchased as a replacement for SILLIAC; however, SILLIAC continued on for a while longer as part of the Sydney University cluster of computers at the Basser Computer Laboratory, where it was connected to the KDF9 and several other computers, creating one of the first Local Area Networks. The KDF9 was used to create mathematical plots and was among the first computers in Australia to develop Computer Graphics. The KDF9 was decommissioned in 1968.
Some Technical details:
The design of the KDF9 was based on the concept for an address-less programming language designed by Charles Hamblin called “GEORGE”, where arithmetic operations were carried out on values in a stack. The KDF9 had two stacks: one for values and the other for return addresses when subroutines were called. Both stacks had 16 words. This design reduced the size of instructions to as little as one unit of 8 bits. This had three advantages: Integer addition and subtraction took 1 microsecond; it reduced the data traffic between the processor and the memory; and compilation of programs took less time. The latter had the fortunate outcome of using Reverse Polish Notation. Translation of an algebraic expression to Reverse Polish Notation inherently produced a sequence of names and operators that was in perfect order for producing the corresponding machine instructions: names corresponded to an instruction to fetch from memory, while operators corresponded to an instruction to carry out the required arithmetic operation. Having values in a stack made it convenient to duplicate the top of the stack and to rearrange some values in the stack, including swapping the top two values. These operations were fast. Multiplication and division, whether integer or floating-point, were also quick. Multiplication took 14 to 18 microseconds, and division took 30 to 35 microseconds. Shifts took from 1 to 4 microseconds.
With a 48-bit word, the KDF9 could handle half-length and double-length values.
Solving 100 simultaneous equations took 15 seconds on KDF9, the program occupying only 36 words. SILLIAC's L2 equivalent took 4 minutes, including input-output, with a maximum of 39 equations.
At 1000 characters per second, the KDF9 paper tape reader was four times faster than SILLIAC, and the paper tape punch was twice as fast. Input-output devices had their own controllers.
"Worth a Thousand Words" by F.M. Larkin 1967 used with permission from Graham Larkin. To see the original film, visit: youtube.com/watch?v=JaHqzQtaVmM&t=677s
State of Electronics is working hard to bring this series to you, but we need your help. Acquiring and licensing images and filmed footage is both time-consuming and expensive. We have set up a GoFundMe campaign to help with this process. You can greatly assist us by donating here: gofund.me/be05614f
Please note: No Ai training is allowed on this channel. Do not replicate any part of this film in part or whole.
You are free to link back to this uploaded video on YouTube.
