A good machine for running a typical Harvest server will have a reasonably fast processor (e.g., Sun Sparc 5, DEC Alpha, Intel Pentium), 1-2 GB of free disk, and 64 MB of RAM. A slower CPU (e.g., a Sun 4) will work but it will slow down the Harvest server. More important than CPU speed, however, is memory size. Harvest uses a number of processes, some of which provide needed ``plumbing'' (e.g., BrokerQuery.pl.cgi), and some of which improve performance (e.g., the Object Cache and its parallel dnsserver processes, and the glimpseserver process). If you do not have enough memory, your system will page too much, and drastically reduce performance. The other factor affecting RAM usage is how much data you are trying to index in a Harvest Broker. The more data, the more disk I/O will be performed at query time, the more RAM it will take to provide a reasonable sized disk buffer pool.
The amount of disk you'll need depends on how much data you want to index in a single Broker. (It is possible to distribute your index over multiple Brokers if it gets too large for one disk.) A good rule of thumb is that you will need about 10% as much disk to hold the Gatherer and Broker databases as the total size of the data you want to index. The actual space needs will vary depending on the type of data you are indexing. For example, PostScript achieves a much higher indexing space reduction than HTML, because so much of the PostScript data (such as page positioning information) is discarded when building the index.
You will need another 50MB of free disk space to run a Harvest Object Cache, or more if you want to run a widely shared cache (e.g., a company-wide ``root'' cache, under which there a number of subordinate caches).