Parallel Computer Architecture

40

CHAPTER

1 Introduction

programmer

in a

message-passing library, forming

a

layer

of

software between send

and receive calls and the actual hardware.

5

The direct FIFO design was soon replaced

by

more versatile

and

more robust

designs that provided direct memory access (DMA) transfers

on

either

end of the

communication event.

A

DMA device

is a

special-purpose controller that transfers

data between memory and

an

I/O device without engaging

the

processor until

the

transfer is complete. The use of DMA allowed nonblocking

sends,

where the sender

is

able

to

initiate

a

send

and

continue with useful computation

(or

even perform

a

receive) while th ...