IBM 7090

The IBM 7090 is a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computer that was designed for "large-scale scientific and technological applications". The 7090 is the fourth member of the IBM 700/7000 series scientific computers. The first 7090 installation was in December 1959. In 1960, a typical system sold for $2.9 million (equivalent to $ million in ) or could be rented for $63,500 a month ().
The 7090 uses a 36-bit word length, with an address space of 32,768 words (15-bit addresses). It operates with a basic memory cycle of 2.18 μs, using the IBM 7302 Core Storage core memory technology from the IBM 7030 (Stretch) project.
With a processing speed of around 100 Kflop/s, the 7090 is six times faster than the 709, and could be rented for half the price. An upgraded version, the 7094 was up to twice as fast. It was withdrawn from sale on July 14, 1969, but systems remained in service for more than a decade after.
Development and naming.
Although the 709 was a superior machine to its predecessor, the 704, it was being built and sold at the time that transistor circuitry was supplanting vacuum tube circuits. Hence, IBM redeployed its 709 engineering group to the design of a transistorized successor. That project became called the 709-T (for "transistorized"), which because of the sound when spoken, quickly shifted to the nomenclature 7090 (i.e., seven - oh - ninety). Similarly, the related machines such as the 7070 and other 7000 series equipment were sometimes called by names of digit - digit - decade (e.g., seven - oh - seventy).
IBM 7094.
An upgraded version, the IBM 7094, was first installed in September 1962. It has seven index registers, instead of three on the earlier machines. The 7094 console has a distinctive box on top that displays lights for the four new index registers. The 7094 introduced double-precision floating point and additional instructions, but is largely backward compatible with the 7090. 
Although the 7094 has 4 more index registers than the 709 and 7090, at power-on time it is in "multiple tag mode", compatible with the 709 and 7090, and requires a Leave Multiple Tag Mode instruction in order to enter "seven index register mode" and use all 7 index registers. In multiple tag mode, when more than one bit is set in the tag field, the contents of the two or three selected index registers are ORed, not added, together, before the decrement takes place. In seven index register mode, if the three-bit tag field is not zero, it selects just one of seven index registers, however, the program can return to multiple tag mode with the instruction Enter Multiple Tag Mode, restoring 7090 compatibility.
In April 1964, the first 7094 II was installed, which had almost twice as much general speed as the 7094 due to a faster clock cycle, dual memory banks and improved overlap of instruction execution, an early instance of pipelined design.
IBM 7040/7044.
In 1963, IBM introduced two new, lower cost machines called the IBM 7040 and 7044. They have a 36-bit architecture based on the 7090, but with some instructions omitted or optional, and simplified input/output that allows the use of more modern, higher performance peripherals from the IBM 1400 series.
7094/7044 Direct Coupled System.
The 7094/7044 Direct Coupled System (DCS) was initially developed by an IBM customer, the Aerospace Corporation, seeking greater cost efficiency and scheduling flexibility than IBM's IBSYS tape operating system provided. DCS used a less expensive IBM 7044 to handle Input/Output (I/O) with the 7094 performing mostly computation. Aerospace developed the Direct Couple operating system, an extension to IBSYS, which was shared with other IBM customers. IBM later introduced the DCS as a product.
Transistors and circuitry.
The 7090 used more than 50,000 germanium alloy-junction transistors and (faster) germanium diffused junction drift transistors.
The 7090 used the Standard Modular System (SMS) cards using current-mode logic some using diffused junction drift transistors.
Instruction and data formats.
The basic instruction format were the same as the IBM 709:
The documentation of opcodes used signed octal
The flag field indicated whether to use indirect addressing or not. The decrement field often contained an immediate operand to modify the results of the operation, or was used to further define the instruction type. The tag field might describe an index register to be operated on, or be used as described below. The Y field might contain an address, an immediate operand or an opcode modifier. For instructions where the tag field indicated indexing, the operation was
If there was no F field or F is not all one bits, then the above was the "effective address". Otherwise it was an "indirect effective address"; i.e., fetch the word at that location and treat the T and Y fields as described above.
Data formats are
Octal notation was used in documentation and programming; console displays lights and switches were grouped into three-bit fields for easy conversion to and from octal.
Input/Output.
The 7090 series features a data channel architecture for input and output, a forerunner of modern direct memory access I/O. Up to eight data channels can be attached, with up to ten IBM 729 tape drives attached to each channel. The data channels have their own very limited set of operations called commands. These are used with tape (and later, disk) storage as well as card units and printers, and offered high performance for the time. Printing and punched card I/O, however, employed the same modified unit record equipment introduced with the 704 and was slow. It became common to use a less expensive IBM 1401 computer to read cards onto magnetic tape for transfer to the 7090/94. Output would be written onto tape and transferred to the 1401 for printing or card punching using its much faster peripherals, notably the IBM 1403 line printer.
Later IBM introduced the 7094/7044 Direct Coupled System; the 7044 handled "spooling" between its fast 1400-series peripherals and 1301 or 1302 disk files, and used data channel to data channel communication as the 7094's interface to spooled data, with the 7094 
primarily performing computations. There is also a 7090/7040 DCS.
Software.
The 7090 and 7094 machines were quite successful for their time, and had a wide
variety of software provided for them by IBM. In addition, there was a very active user community within the user organization, SHARE.
IBSYS is a "heavy duty" production operating system with numerous subsystem and language support options, among them FORTRAN, COBOL, SORT/MERGE, the MAP assembler, and others.
FMS, the Fortran Monitor System, was a more lightweight but still very effective system optimized for batch FORTRAN and assembler programming. The assembler provided, FAP, (FORTRAN Assembly Program), was somewhat less complete than MAP, but provided excellent capabilities for the era. FMS also incorporated a considerably enhanced derivative of the FORTRAN compiler originally written for the 704 by Backus and his team.