CDC 6600

CDC 6600
Manufacturer:	Control Data Corporation
Year Announced:	September, 1964
Year First Shipped:	1965
Form Factor:	mainframe
Word Size:	60 bits
Clock Speed:	10 MHz
Memory Size:	128K words (max)
Memory Speed:	1 μsecond (cycle time)
Physical Address Size:	17 bits
Memory Management:	base and bounds
Operating System:	SCOPE. KRONOS
Predecessor(s):	none
Successor(s):	CDC 7600
Price:	US$2.4M

The CDC 6600 was an influential early (1964) mainframe computer. It is generally considered the first supercomputer, three times faster then the IBM 7030 Stretch, the previous fastest computer record-holder; the 6600 held the title from 1965 to 1969. It was the first computer to use a superscalar internal architecture (although the term 'superscalar' did not exist at that time).

It used a RISC-like approach, in that instructions were simple, doing only one thing; the instruction set was basically load-store. Instructions took a minimum of three clock ticks.

It had ten independent 'functional units' in the CPU:

• branch
• boolean
• shift
• long integer add
• floating point add
• floating point multiply (two)
• floating point divide
• incrementers (two; also performed memory operations)

Each instruction was routed to the appropriate functional unit, which, if idle, could begin executing right away. (For the duplexed functional units, assignment alternated.) The units were not pipelined, a refinement that was introduced with the 6600's successor, the CDC 7600.

The CPU did not do any I/O; that was left to a set of ten 'Peripheral Processors', which shared access to the main memory (which had a 32-way interleave to maximize throughput).

In addition to the main memory, the 6600 was later upgraded with an 'Extender Core Storage' unit, with a cycle time of 3.2 μseconds, holding up to 2 megawords. This was intended to smooth out the large performance gap in the storage hierarchy between main memory and disk.

The 6600 was built using then-new silicon transistors, and the physical arrangement was designed to minimize conductor lengths, to minimize 'speed of light' delays.

Further reading

• Jim E. Thornton, Design of A Computer: The Control Data 6600, Scott, Foresman, Glenview, 1970