Online Encyclopedia
IBM 700/7000 series
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 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).
First Architecture (701)
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.
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
Data Formats
Numbers were 36 bits long, both fixed point and floating point. (See: Why 36 bits?)
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 perfomed 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 (705)
Data format
Data was represented by a variable length string of characters terminated by a Record mark.
Registers
- Accumulator - 256 characters
- one auxiliary storage unit - 32 characters
- 14 auxiliary storage units - 16 characters
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.
Decimal Architecture (7070/7074)
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 9900 words
- Add time - 72 microseconds (7070)
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
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