INTRODUCTION Architecture Organization Architecture is those attributes visible

INTRODUCTION Architecture & Organization • Architecture is those attributes visible to the programmer – Instruction set, number of bits used for data representation, I/O mechanisms, addressing techniques. – e. g. Is there a multiply instruction? • Organization is how features are implemented – Control signals, interfaces, memory technology. – e. g. Is there a hardware multiply unit or is it done by repeated addition?

• All Intel x 86 family share the same basic architecture • The IBM System/370 family share the same basic architecture • This gives code compatibility • Organization differs between different versions

Designing for performance: Factors influencing the design for performance: 1. Microprocessor Speed: – Pipelining – On board cache – On board L 1 & L 2 cache – Branch prediction – Data flow analysis – Speculative execution

The increasing speed improves the performance 4 or 5 fold every 3 years. The addition of new circuits and reducing the distance between them increases the speed. In addition to this the processor designer uses some techniques to improve the processor speed. Pipelining is the process of overlapping the different phases of execution By having on board cache the access time can be reduced. Modern computers have different levels of cache on the board

Branch prediction: The processor looks ahead in the instruction code fetched from memory and predicts which branches or groups of instructions are likely to be processed next. So the processor will always be busy Data flow analysis: The processor analyses which instructions are dependent on each others results or data to create an optimized schedule of instructions In fact instructions are scheduled to be executed when ready, independent of the original program order. This prevents unnecessary delay.

Speculative execution: Using branch prediction and data flow analysis, some processors execute instructions ahead of their actual appearance in the program execution holding the results in temporary locations

2. Performance Balance: This is an adjusting of the organization and architecture to compensate for the mismatch among the capabilities of the various components. Such mismatch arises in the interface between processor and main memory due to the following:

• Increased Processor Speed • Increased Memory Capacity • Memory speed lags behind processor speed

Solutions • Increase number of bits retrieved at one time – Make DRAM “wider” rather than “deeper” • Change DRAM interface – Cache • Reduce frequency of memory access – More complex cache and cache on chip • Increase interconnection bandwidth – High speed buses – Hierarchy of buses

I/O Devices • Another area of design focus is the handling of I/O devices. While the processor can handle the data pumped out by I/O devices, there is the problem of getting that data moved between processor and peripherals. In this case the use of multiple processors can aid in satisfying I/O demands.

• Solutions: – Caching – Buffering – Higher-speed interconnection buses – More elaborate bus structures – Multiple-processor configurations

Key is Balance • • Processor components Main memory I/O devices Interconnection structures

Pentium Evolution: • 8080 – first general purpose microprocessor – 8 bit data path – Used in first personal computer • 8086 – much more powerful – 16 bit data path – instruction cache, prefetch few instructions – 8088 (8 bit external bus) used in first IBM PC • 80286 – 16 Mbyte memory

• 80386 – 32 bit – Support for multitasking • 80486 – sophisticated powerful cache and instruction pipelining – built in maths co-processor • Pentium – Superscalar – Multiple instructions executed in parallel • Pentium Pro – Increased superscalar organization – Aggressive register renaming – branch prediction – data flow analysis – speculative execution

• Pentium II – MMX technology – graphics, video & audio processing • Pentium III – Additional floating point instructions for 3 D graphics • Pentium 4 – Further floating point and multimedia enhancements • Itanium – 64 bit organization with the IA-64 architecture • Itanium 2 – Hardware enhancements to increase speed

Power. PC Evolution: • Proposed by IBM in 1975 • Berkeley RISC I processor • 1986, IBM commercial RISC workstation product, RT PC. – Not commercial success – Many rivals with comparable or better performance • 1990, IBM RISC System/6000 – RISC-like superscalar machine – POWER architecture

• IBM entered into an alliance with Motorola (68000 microprocessors), and Apple (used 68000 in Macintosh) • Result is Power. PC architecture – Derived from the POWER architecture – Superscalar RISC – Used in Apple Macintosh & Embedded chip applications

Power. PC Family: • 601: – First Power. PC -- 32 -bit machine • 603: – Low-end desktop and portable – 32 -bit – Comparable performance with 601 – Lower cost and more efficient implementation

• 604: – Desktop and low-end servers – 32 -bit machine – Much more advanced superscalar design – Greater performance • 620: – High-end servers – 64 -bit architecture

• 740/750: – Also known as G 3 – Two levels of cache on chip • G 4: – Increases parallelism and internal speed • G 5: – Improvements in parallelism and internal speed – 64 -bit organization