Even with a brand new PC it's likely that some other internal system is the bottleneck. The tightest bottleneck on either of the two PC's will be the limit of the data flow.

Typical Motherboard Architecture

Typically traffic from the NIC would be written directly to a memory space set aside by the operating system for it. This type of transfer is known as "Direct Memory Access" (DMA) and handled mostly by the chip sets. The processor has to strip the remaining IP headers, determine where to place the data, prepare the data for disk access and finally write the data to the DMA space reserved for disk writes. The data travels back to the SouthBridge formatted in clusters and written to disk. The two trips through the bus and the multiple memory reads/writes are all in contention with other system services. If either the disk controller or the NIC is on the PCI there will be contention for the PCI bus.

The internal speed of the hard disk is the most likely bottleneck. You can help yourself here by ensuring that DMA is enabled. Follow these steps to get the most out of your current hard drive system. Obviously any system using the ATA/100 and below will never see full gigabit performance.

These transfer speeds were obtained from Sisoft Sandra's benchmarking suites.T My hard disk (purchased mid 2004 )tested at 47MB/sec.

ATA133 with Western Digital 120GB DiamondMax Plus 31MB/sec 248Mbs

SATA150 with Maxtor 120GB MaxLine Plus II 29MB/sec 232Mbs

SCSI U160 with Maxtor 18GB AtlasIV (15K RPM) 39MB/sec 312Mbs

SATA with 2*WD Raptor (raid 0) 95MB/sec 760Mbs

SCSI U320 with 2xMaxtor AtlasIV 115MB/sec 920Mbs

SATA with 4*WD Raptor (raid 0) 144MB/sec 1.15 Gbs

The next most likely bottleneck would be the PCI bus interface. This interface is shared among all devices. Your RAID controller card and and nic traffic would have to traverse the same bus unless these devices were built into the chipset. A server type system with multiple PCI controllers would also help. The PCI bus runs at the speed of the slowest card on the bus, so an old sound card could be limiting the rest of the peripherals.

PCI Bus theoretical limits

Shared among all devices

PCI-32/33 132MB/sec (1 Gbs)

PCI-64/66 512MB/sec (4 Gbs)

PCI-X-133 1GB/s (8 Gbs)

Bandwidth exclusive to each device Intel 900, Via K8T890

PCI-Express 250MB/sec (2Gbs) (each way).

Some other contributing factors could be a shortage of memory since additional disk writes will be necessary to clear a space for the processing. Other applications (or even the OS) accessing memory, the disks or using processor cycles while the transfer is in process could also affect the speed.