The SiS645 integrates a high performance host interface for Intel Pentium 4 processor, a high performance memory controller, a AGP interface, and SiS MuTIOL® Technology connecting w/ SiS961 MuTIOL® Media I/O.

The SiS645 Host Interface features the AGTL & AGTL+ compliant bus driver technology with integrated on-die termination to support Intel Pentium 4 series processors with FSB up to 400MHz. It provides a 12-level In-Order-Queue to support maximum outstanding transactions on host bus up to 12. The host interface plays the role of processor transactions!| dispatcher. It dispatches transactions to Memory, I/O interface and AGP bus. Transactions to different destinations can be dispatched concurrently in order to maximum pipeline efficiency. In addition to dispatching processor!|s transactions to corresponding destinations, host interface also forward DMA transactions from AGP masters and I/O masters to host bus for snooping, including master interrupt delivery.

The memory controller can support both DDR and SDR. It can offer bandwidth up to 2.7GB/s under DDR333 and 1GB/s under PC133 in order to sustain the bandwidth demand from host processor, as well as the multi I/O masters and AGP masters. The Memory Controller mainly comprises the Memory Arbiter, the M-data/ M-Command Queues, and the Memory Interface. The Memory Arbiter arbitrates a plenty of memory access Host Controller, and I/O bus masters based on a default optimized priority list with the capability of dynamically prioritizing the I/O bus master requests in a bid to offering privileged service to 1) the isochronous downstream transfer to guarantee the min. latency & timely delivery, or 2) the PCI master upstream transfer to curb the latency within the maximum tolerant period of 10us. Prior to the memory access requests pushed into the M-data queue, any command compliant to the paging mechanism is generated and pushed into the M-CMD queue. The M-data/M-CMD Queues further orders and forwards these queuing requests to the Memory Interface in an effort to utilizing the memory bandwidth to its utmost by scheduling the command requests in the background when the data requests streamlines in the foreground. The memory controller also supports the Suspend to RAM function by retaining the CKE# pins asserted in ACPI S3 state in which only AUX source deliver power.

The AGP interface can support external AGP slot with AGP 1X/2X/4X capability and Fast Write Transactions. A high bandwidth and mature SiS MuTIOL® technology is incorporated to connect SiS645 and SiS961 MuTIOL® Media I/O together. SiS MuTIOL® technology is developed into three layers, the Multi-threaded I/O Link Layer delivering 1.2GB bandwidth to connect embedded DMA Master devices and external PCI masters to interface to Multi-threaded I/O Link layer, the Multi-threaded I/O Link Encoder/Decoder in SiS961 to transfer data w/ 533 MB/s bandwidth from/to Multi-threaded I/O Link layer to/from SiS645, and the Multi-threaded I/O Link Encoder/Decoder in SiS645 to transfer data w/ 533 MB/s from/to memory sub-system to/from the Multi-threaded I/O Link Encoder/Decoder in SiS961.