MANUEL DUARTE

Hardware Configuration

This section shows the emulator configuration with the PowerMac G5 hosting the SIMH VAX 3900 emulator. The emulator and associated disk files reside on a solid state disk for improved disk access speed. A small 100GB disk is sufficient for hosting VMS and the emulated disk drives. The PowerMac is connected to a 1GB switch as its Ethernet adapter operates at 1GB full duplex. The two VAX satellites have 10 MBit Ethernet adapters and are connected to a 10/100 MBit switch. The PowerMac's network capacity is more than adequate to support the physical VAX systems with bandwidth to spare as a boot node. The one issue that could become a network bottleneck for the satellites is that each system (DODO and HAWK) pages and swaps to TINY system disk. Having the satellites page and swap to their own local disks would reduce network use and improve the satellite node's performance. However, as there are only two satellite nodes, TINY's SSD disk should be able to support the I/O demand from the satellites without performance degradation on the G5's disk or CPU. The emulator configuration and network topology is illustrated in Figure 1.

Figure 1

Source: M. Duarte

The PowerMac G5 remains a great low cost system for SIMH emulation. With two 64-bit G5 PowerPC processors operating at 2.3GHz, built-in vector processor (AltiVec) per processor, a 512K L2 cache per processor, 1GHz network adapter and a 1GHz frontside bus per processor makes this a system that can exceed the performance of the physical VAX 3900 it emulates. The VAX emulator image for the G5 is about 800K in size, it almost fits within the 512K cache. On more current systems (Intel based Apple systems) with processors featuring internal caches in the 9 MByte range, the emulator could easily reside in cache and benefit from a speed increase.

When I was working at CAE Electronics, our software group built a Xerox Sigma emulator on a 32-bit ENCORE 32/87 system. The emulator resided fully in cache and replaced an aging Sigma computer on an older flight simulator. The benefits of the emulator residing fully in cache were evident through the fast emulator execution that bettered the Sigma's execution speed.

The table below lists system specifications of the actual VAX hardware based systems. Note the smaller processor caches in these early VAX systems. The on-chip and the L2 on-board caches are quite small in comparison to those on more current CPUs.

System Specifications