Cray T3E Architecture

Cray T3E architecture are microprocessor for super-computing system. Cray T3E is a RISC(Reduced Instruction Set Computer) architecture which is very powerful microprocessors. T3E systems contain a large number of processing elements (PE). Each PE consists of a DEC Alpha EV5 RISC microprocessor.

Design features of Cray T3E architecture are as follows:

• The CRAY T3E is a scalable shared-memory multiprocessor
• The system architecture is designed to tolerate latency and enhance scalability.
• The T3E system was fully self-hosted and ran the UNICOS/mk distributed operating system.
• Cray T3E scalability can handle added processors and memory as well as larger I/O and interconnection bandwidths.
• Broad range implementation
• Cray T3E system has their own local memory.

Cray T3E Architecture:

1. Memory:
   T3E has its own local memory with capacity from 64 megabytes to 2 gigabytes. All address are represented using bytes. Two consecutive bytes form a word, four bytes form a longword, eight bytes form a quadword.
2. Register:
   The Alpha architecture includes 32 general-purpose register from R0 to R31. R31 always contain the value zero. Each general-purpose register in Alpha architecture of Cray T3E system is 64-bit long. Other than 32 general-purpose register there are also 32 floating-point registers from F0 to F31 and F31 always contain zero value. Each floating-point register have 64-bit length.
3. Data Formats:
   • Integers are stored as longwords or quadwords.
   • Characters are represented using 8-bit ASCII codes.
   • Floating points are represented using two different floating-point formats.
4. Instruction Formats:
   In Cray T3E architecture there are basically five instruction formats. All of these formats are 32 bit long and first 6 bits of the instruction word represents the opcode. Some instruction formats also have an “functional” field in which function of different registers are specified.
5. Addressing Modes:
   Just like in most of the RISC architectures, the only instructions that deals with memory are load, store and branch instructions.
   There are two modes to address operands in memory:

   Mode                      Target address(TA) calculation
   PC-relative               TA=(PC) + displacement
   
   Register indirect         TA=(register) + displacement
   with displacement 

   Register indirect with displacement mode is used for load, store and subroutine jumps operations.
   PC-relative mode is used for conditional and unconditional branches.

6. Instruction Set:
   Cray T3E architecture has approximately 130 machine instructions. Cray T3E architecture uses a large number of instructions to do the implementation of operations as fast as possible.
7. Input and Output:
   Cray T3E architecture uses multiple ports to perform I/O. These multiple ports have one or more I/O channels, which are integrated into the network that interconnects the processing nodes. All these channels are controllable and accessible from all PE’s (Processing Elements).