The IBM System/360 A Brief History 1964 -- announced 1965 -- - - PowerPoint PPT Presentation

The IBM System/360

A Brief History

• 1964 -- announced
• 1965 -- shipped (vs. CDC6600 in 1964)
• 6 models initially announced
• Hundreds of compatible peripherals

IBM Wants to Make More Money!

• They want to sell computers to everyone!
• Small businesses, Big business, and in

between

• They want to grow with their customers
• They want “lock in”!
• They also want to reduce development

costs

• Amortize work over several machines.

Fundamental Observation

• The programmer’s view of the machine (its

“Architecture”) and the organization of the hardware that implements it need not be the same.

• Separating them allows you to build a binary

compatible family of machines.

• The only thing different is the speed/capacity
• “That machine too slow/small? We’ll sell you a

faster one!”

A Family of Machines

• Strict binary compatibility
• Standardized, asynchronous peripheral

interface

• Scalable up and down
• across a wider range than we see today.

Key Features

• 8-bit byte/32 bit words
• There were big fights about this.
• Byte addressability
• General-purpose ISA
• Floating point standard (eventually absorbed by IEEE FP

standard)

• 2’s compliment arithmetic
• Relocatability

Tomasulo’s Algorithm

• Second way to do out-of-order
• Introduced in IBM360-91 -- 1968
• Example of separating Architecture from

impl

Tomasulo’s Algorithm

In Context

• Hugely influential
• Many key innovations as discussed
• Not only invented ideas but set standards

Compared to the CDC6600

• The System/360 is for business (mostly).
• The CDC6600 is a super computer.
• Very different goals
• Good for business environments vs. fast fast

fast

• This dichotomy still exists, although it is

shrinking.