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IBM 700/7000 series

From Academic Kids

The IBM 700/7000 series was a series of incompatible large scale (mainframe) computer systems made by IBM through the 1950s and early 1960s. The 700's were all made obsolete by the introduction of the 7000s. The 7000s, in turn, were eventually replaced by System/360, which was announced in 1964. However the 360/65, the first 360 powerful enough to replace 7000s, did not become available until November 1965. Early problems with OS/360 and the high cost of converting software kept many 7000's in service for years afterwards.

Contents

Architectures

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

  • First (36/18-bit words): 701 (Defense Calculator)
  • Scientific (36-bit words): 704, 709, 7090, 7094, 7040, 7044
  • Commercial (variable length character strings): 702, 705, 7080, 7010
  • Decimal (10 digit words): 7070, 7074
  • Supercomputer (64-bit words): 7030 "Stretch"

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 and the 702 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 some 360 models 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).

First Architecture (701)

Known as the Defense Calculator while in development in the IBM Poughkeepsie Laboratory, this machine was formally unveiled April 7, 1953 as the IBM 701 Electronic Data Processing Machine.

Data Formats

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

Instruction Format

Instructions were 18 bits long, single address.

  • Sign (1 bit) - Whole word (-) or Half word (+) operand address
  • Opcode (5 bits) - 32 instructions
  • Address (12 bits) - 4096 Half word addresses

Registers

  • AC  - 38-bit Accumulator
  • MQ - 36-bit Multiplier-Quotient

Memory

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

Scientific Architecture (704/709/7090/7094)

Data Formats

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

  • Fixed point numbers were stored in binary sign/magnitude format.
  • Single precision floating point numbers had a magnitude sign, an 8-bit excess-128 exponent and a 29 bit magnitude
  • Double precision floating point numbers, introduced on the 7094, had a magnitude sign, a 17-bit excess-65536 exponent, and a 54 bit magnitude
  • Alphanumeric characters were 6-bit BCD, packed six to a word.

Instruction Format

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 registers, 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.

Registers

  • AC  - 38-bit Accumulator
  • 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 magnitude 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.

Memory

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

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.

Commercial Architecture (702/705/7080)

The IBM 702 and 705 were similar and the 705 could run many 702 programs without modification, but they were not completely compatible.

The IBM 7080 was a transistorized version of the 705, with various improvements.

Data format

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

Instruction Format

Five characters: one character opcode & 4 character address - OAAAA

Registers

  • 702
    • two Accumulators (A & B) - 512 characters
  • 705
    • one Accumulator - 256 characters
    • 14 auxiliary storage units - 16 characters
    • one auxiliary storage unit - 32 characters
  • 7080
    • one Accumulator - 256 characters
    • 30 auxiliary storage units - 512 characters
    • 32 communication storage units - 8 characters

Memory

  • 702
    • 2,000 to 10,000 characters in Williams tubes (in increments of 2,000 characters)
    • Character cycle rate - 23 microseconds
  • 705 (models I, II, or III)
    • 20,000 or 40,000 or 80,000 characters of Core memory
    • Character cycle rate - 17 microseconds or 9.8 microseconds
  • 7080
    • 40,000 or 80,000 or 160,000 characters of Core memory
    • Character cycle rate - 2.18 microseconds

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

Decimal Architecture (7070/7074)

The IBM 7070 and IBM 7074 were designed to provide a "transistorized IBM 650" upgrade path. They replaced the drum memory with core memory, but were not instruction set compatible with the 650 (so a simulator was needed to run old programs).

Data format

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

Instruction format

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

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)

Memory

  • 5000 to 9990 words
  • Access time - 6 microseconds (7070), 4 microseconds (7074)
  • Add time - 72 microseconds (7070), 10 microseconds (7074)

IBM 700 series, vacuum tubes, 1950s

IBM 7000 series, transistors, 1960s

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