[8] When the system was released in 1967, it sold for around $5 million in base configurations,[9] and considerably more as options and features were added.

[11] As the 6600 neared production quality, Cray lost interest in it and turned to designing its replacement.

Making a machine "somewhat" faster would not be too difficult in the late 1960s; the introduction of integrated circuits allowed denser packing of components and, in turn, a higher clock speed.

However, as with the 6600 design, Cray set himself the goal of producing a machine with ten times the performance.

That way, as soon as the current instruction completes and moves to the output circuitry, the operands for the next addition are already waiting to be added.

The improvement in performance generally depends on the number of steps the unit takes to complete.

To achieve the rest of the goal, the machine would have to run at a faster speed, now possible using new transistor designs.

As always, Cray's design work spent considerable effort on this problem and thus allow higher operating frequencies.

Roush added an aluminum plate to the back of each side of the cordwood stack, which were in turn cooled by a liquid-freon system[15] running through the core of the machine.

Since this system was mechanical, and therefore prone to failure, the 7600 was redesigned into a large "C" shape to allow access to the modules on either side of the cooling piping by walking into the inside of the "C" and opening the cabinet.

[16] The CDC 7600 "was designed to be machine code upward compatible with the 6600, but to provide a substantial increase in performance".

"[8] Although the 7600 shared many features of the 6600, including hardware, instructions, and its 60-bit word size, it was not object-code compatible with the CDC 6600.

However, due to the 7600's operating system design, the 6600 and 7600 shared a "uniform software environment" despite the low-level differences.

At the time computer memory could be arranged in blocks with independent access paths, and Cray's designs used this to their advantage.

In order to take advantage of this, the 6600 and 7600 left mundane housekeeping tasks, printing output or reading punched cards, for instance, to a series of ten smaller 12-bit machines based on the CDC 160-A known as "Peripheral Processor Units", or PPUs.

[21] For any given cycle of the machine one of the PPUs was in control, feeding data into the memory while the main processor was crunching numbers.

However, the instruction set itself had changed to reflect the new internal memory layout, thereby rendering it incompatible with the earlier 6600.

The machine initially did not come with software; sites had to be willing to write their own operating system, like LTSS, NCAROS, and others; and compilers like LRLTRAN (Livermore's version of Fortran with dynamic memory management and other non-standard features).