IBM 700/7000 Series Architectures First Architecture (701)

The IBM 700/7000 series had five completely different ways of storing data and instructions:

The 700 class used vacuum tubes, the 7000 class was transistorized. All machines (like most other computers of the time) used magnetic core memory, except for early 701 models using CRT memory. While the architectures differed, the machines in the same class shared electronics technologies and generally used the same peripherals (tape drives, card readers, card punches). Early peripherals were based on IBM accounting machine technology and even had wiring boards. Later peripherals were adopted from the midline IBM 1400 series.

Early computers were sold without software. As operating systems began to emerge, having four different mainframe architectures plus the 1400 midline architectures became a major problem for IBM since it meant at least four different programming efforts were required.

The System/360 combined the best features of the 7000 and 1400 series architectures into a single design, however the larger 360's had optional features that allowed them to emulate the 1400 and 7000 instruction sets in microcode. One of the selling points of the System/370 was improved 1400/7000 series emulation (it could be done under operating system control instead of shutting down and restarting in emulation mode as was done on the 360s).

2 First Architecture (701)

2.1 Data Formats

Numbers were either 36 bits or 18 bits long, only fixed point. (See: Why 36 bits?)

2.2 Instruction FormatAn instruction set or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception han

2.3 RegistersIn computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a

2.4 Memory

2,048 or 4,096 – 36-bit binary words with six-bit characters

3 Scientific Architecture

3.1 Data Formats

Numbers were 36 bits long, both fixed point and floating point. (See: Why 36 bits?)

3.2 Instruction FormatAn instruction set or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception han

The basic instruction format was a 3-bit prefix, 15-bit decrement, 3-bit tag, and 15-bit address. The prefix field specified the class of instruction. 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 three bits of the tag specified three (seven in the 7094) index registerAn index register in a computer CPU is a processor register used for modifying operand addresses during the run of a program, typically for doing vector/ array operations. Index registers were first used in the British Manchester Mark I computer, in 1949.s, the contents of which were subtracted from the address to produce an effective address. The address field either contained an address or an immediate operand.

3.3 RegistersIn computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a

AC - 38-bit AccumulatorIn a CPU, an accumulator is a register in which intermediate results are stored. Without an accumulator, it would be necessary to write the result of each calculation (addition, multiplication, shift, etc. to main memory and read them back. Access to main
MQ - 36-bit Multiplier-Quotient
XR - 15-bit Index Registers (three or seven)
SI - 36-bit Sense Indicator

The Accumulator (and Multiplier-Quotient) registers operated in signed magnitudeComputer arithmetic One of the common misunderstandings among computer users is a certain faith in the infallibility of numerical computations. That is, if you multiply, say: : you might expect to get a result of exactly 1. In practice, the result may pro format.

The Index registers operated using two's complement format and when used to modify an instruction address were subtracted from the address in the instruction. On machines with three index registers, if the tag had 2 or 3 bits set (i.e. selected multiple registers) then their values were ORed together before being subtracted. The IBM 7094, with seven index registers had a "compatibility" mode to permit programs from earlier machines that used this trick to continue to be used.

The Sense Indicators permitted interaction with the operator via panel switches and lights.

3.4 Memory

32,768 – 36-bit binary words with six-bit characters

3.5 Input/Output

The 709/7090 series used Data Synchronizer Channels for high speed input/output, such as tape and disk. The DSCs executed their own simple programs from the computer memory that controlled the transfer of data between memory and the I/O devices. Punch card I/O and high speed printing were often performed by transferring magnetic tapes to an off-line IBM 1401. Later, the data channels were used to connect an 7094 and a 7044 to form the IBM 7094/7044 Direct Coupled System (DCS). In that configuration, the 7044 primarily handled I/O.

4 Commercial Architecture (705)

4.1 Data format

Data was represented by a variable length string of characters terminated by a Record mark.

4.2 Registers

Accumulator - 256 characters
one auxiliary storage unit - 32 characters
14 auxiliary storage units - 16 characters

4.3 Memory

20,000 characters
Character cycle rate - 17 microseconds

The 700/7000 commercial architecture also spawned the very successful IBM 1400 series of mid-sized business computers.

5 Decimal Architecture (7070/7074)

5.1 Data format

Word length - 10 decimal digit plus sign
Digit encoding - 2 out of 5
Floating point - optional. Two digit exponent.

5.2 Instruction format

All instructions one word
2 digit op code (including sign)
2 digit index register
2 digit field control
4 digit address

5.3 Registers

All registers one word, could also be addressed as memory
Accumulators - 3 (addresses 9991, 9992, and 9993)
Program counter - 1 (address 9995)
Index registers - 99 (addresses 0001-0099)

5.4 Memory

5000 to 9900 words
Add time - 72 microseconds (7070)

6 IBM 700 series, vacuum tubes, 1950s

IBM 701 - IBM's first electronic computer - introduced in 1952
IBM 702 - commercial - introduced in 1953
IBM 704 - scientific - introduced in 1956
IBM 705 - commercial - introduced in 1954
IBM 709 - scientific - introduced in 1958

7 IBM 7000 series, transistors, 1960s

IBM 7010 - commercial - high end version of IBM 1410 - introduced in 1962
IBM 7030 - Stretch supercomputer - introduced in 1960
IBM 7040 - scientific - introduced in 1963
IBM 7044 - scientific - introduced in 1963
IBM 7070 - decimal - introduced in 1958
IBM 7074 - decimal - introduced in 1960
IBM 7080 - commercial - introduced in 1960
IBM 7090 - scientific - introduced in 1959
IBM 7094 - scientific - introduced in 1962
IBM 7094 II - scientific - introduced in 1964

8 External links

IBM hardware Mainframe computers

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